HEXA

UniProt ID: P06865
Organism: Homo sapiens
Review Status: INITIALIZED
📝 Provide Detailed Feedback

Gene Description

HEXA encodes the alpha subunit of lysosomal beta-hexosaminidase, a glycoside hydrolase family 20 (GH20) enzyme (EC 3.2.1.52). With the beta subunit (HEXB) it forms beta-hexosaminidase A, the alpha-beta heterodimer; the beta-beta homodimer is hexosaminidase B and the alpha-alpha homodimer is hexosaminidase S. The enzyme hydrolyses terminal non-reducing beta-linked N-acetyl-D-hexosamine (beta-GalNAc/GlcNAc, including sulfated hexosamine) residues from a range of glycoconjugates. The alpha-subunit active site is uniquely able, together with the GM2-activator protein (GM2A), to hydrolyse the GM2 ganglioside (removing the terminal GalNAc to give GM3); only hexosaminidase A performs this reaction in vivo. Because the alpha active site accepts negatively charged/sulfated substrates, hexosaminidase A/S also degrade sulfated glycosaminoglycan fragments (dermatan sulfate, keratan sulfate) and other glycoconjugates such as the sulfated glycosphingolipid SM2. The enzyme acts in the lysosome / lysosomal lumen. Loss of HEXA activity causes GM2-gangliosidosis type 1 (Tay-Sachs disease), an autosomal-recessive lysosomal storage disease characterised by neuronal accumulation of GM2 ganglioside.

Existing Annotations Review

GO Term Evidence Action Reason
GO:0004563 beta-N-acetylhexosaminidase activity
IBA
GO_REF:0000033 		ACCEPT
Summary: Phylogenetic (IBA) propagation of the family-defining beta-N-acetylhexosaminidase activity. This is the exact molecular function of the HEXA alpha subunit and the core catalytic activity of the enzyme.
Reason: Correct core molecular function, matching the UniProt catalytic activity (EC 3.2.1.52) and multiple independent experimental annotations.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
Hydrolyzes the non-reducing end N-acetyl-D-hexosamine
GO:0005576 extracellular region
IBA
GO_REF:0000033 		KEEP AS NON CORE
Summary: IBA propagation of an extracellular-region location. HEXA is fundamentally a lysosomal enzyme; a fraction is secreted (precursor alpha-beta complexes are secreted), and the enzyme is detected extracellularly, but this is not its core site of action.
Reason: Peripheral/secreted localization of a normally lysosomal hydrolase; retain but not as a core location.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
Lysosome
GO:0005764 lysosome
IBA
GO_REF:0000033 		ACCEPT
Summary: IBA propagation of lysosomal localization, the canonical site of action of beta-hexosaminidase A/S. This is a core cellular component.
Reason: Correct core localization; matches UniProt subcellular location and the acid-hydrolase biology of the enzyme.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
Lysosome
GO:0030203 glycosaminoglycan metabolic process
IBA
GO_REF:0000033 		ACCEPT
Summary: IBA propagation of glycosaminoglycan metabolism. The alpha active site removes terminal (sulfated) hexosamines from GAG fragments such as dermatan sulfate and keratan sulfate, so HEXA participates in lysosomal GAG catabolism.
Reason: Well supported core process; the alpha/Hex A active site degrades sulfated GAG fragments (dermatan/keratan sulfate).
Supporting Evidence:
PMID:11707436
active on water-soluble and amphiphilic glycoconjugates including artificial substrates, sulfated GAG fragments, and the sulfated glycosphingolipid SM2
PMID:6458607
keratan sulfate-derived oligosaccharides with beta-N-acetylhexosaminidase A analogously resulted in the liberation of N-acetylglucosamine-6-sulfate
GO:0006689 ganglioside catabolic process
IBA
GO_REF:0000033 		ACCEPT
Summary: IBA propagation of ganglioside catabolism. The alpha subunit, within Hex A and together with GM2A, is uniquely responsible for GM2 ganglioside degradation. This is a core biological process and the process whose failure causes Tay-Sachs disease.
Reason: Core, alpha-specific process; only Hex A (containing alpha) degrades GM2 in vivo.
Supporting Evidence:
PMID:16698036
Only the alpha-subunit active site can hydrolyze GM2 gangliosides
file:human/HEXA/HEXA-uniprot.txt
Only the isozyme A is responsible for the
GO:0004553 hydrolase activity, hydrolyzing O-glycosyl compounds
IEA
GO_REF:0000002 		ACCEPT
Summary: InterPro2GO electronic mapping to the parent O-glycosyl hydrolase activity. This is a correct but more general parent of the specific GO:0004563 beta-N-acetylhexosaminidase activity.
Reason: Correct (if general) parent term; consistent with the GH20 glycosidase activity and not misleading.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
Belongs to the glycosyl hydrolase 20 family
GO:0004563 beta-N-acetylhexosaminidase activity
IEA
GO_REF:0000120 		ACCEPT
Summary: Electronic (ARBA/InterPro/EC) assignment of the family-defining beta-N-acetylhexosaminidase activity (EC 3.2.1.52), consistent with the experimental catalytic activity.
Reason: Correct core molecular function derived from EC 3.2.1.52 and family membership.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
Hydrolyzes the non-reducing end N-acetyl-D-hexosamine
GO:0005764 lysosome
IEA
GO_REF:0000044 		ACCEPT
Summary: Electronic mapping from the UniProt subcellular location (Lysosome) keyword. Correct core localization.
Reason: Matches the curated UniProt subcellular location and lysosomal biology.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
Lysosome
GO:0005975 carbohydrate metabolic process
IEA
GO_REF:0000002 		ACCEPT
Summary: InterPro2GO electronic mapping to a broad carbohydrate-metabolism process. Correct but very general parent of the specific glycoconjugate/GAG/ganglioside catabolic processes.
Reason: Broad but not incorrect; a high-level parent of the specific catabolic processes captured elsewhere.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
oligosaccharide moieties from proteins and neutral glycolipids, or from
GO:0008375 acetylglucosaminyltransferase activity
IEA
GO_REF:0000117 		REMOVE
Summary: Electronic ARBA assignment of a glycosyltransferase (acetylglucosaminyltransferase) activity. This is biologically incorrect - HEXA is a GH20 glycoside hydrolase (EC 3.2.1.52) that removes terminal hexosamines by hydrolysis, not a transferase that adds GlcNAc. The transferase reading likely arises from misinterpreting N-glycan trimming reports as sugar transfer.
Reason: Wrong enzyme class for an electronic inference; HEXA is a hydrolase, not a glycosyltransferase. This ARBA mapping contradicts the well-established catalytic activity and family assignment.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
Belongs to the glycosyl hydrolase 20 family
GO:0016042 lipid catabolic process
IEA
GO_REF:0000117 		ACCEPT
Summary: Electronic ARBA mapping to lipid catabolism. This is a reasonable broad parent given the role in glycosphingolipid (ganglioside GM2, SM2) degradation.
Reason: Correct high-level parent of glycosphingolipid/ganglioside catabolism; consistent with GM2 and SM2 degradation.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
degradation of GM2 gangliosides in the presence of GM2A
GO:0042582 azurophil granule
IEA
GO_REF:0000117 		KEEP AS NON CORE
Summary: Electronic ARBA mapping to azurophil granule, mirroring the experimental IDA (PMID:25645918) that detected azurophilic-granule-resident beta-hexosaminidase A in neutrophils. A real but non-core, cell-type-specific location.
Reason: Neutrophil azurophil granules are lysosome-related organelles; a legitimate but specialized, non-core location for this normally lysosomal enzyme.
Supporting Evidence:
PMID:25645918
azurophilic granule-resident
GO:0043202 lysosomal lumen
IEA
GO_REF:0000117 		ACCEPT
Summary: Electronic ARBA mapping to lysosomal lumen, the precise compartment where the soluble acid hydrolase acts. Core localization.
Reason: Accurate soluble-lumen localization consistent with UniProt and Reactome.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
Lysosome
GO:1901135 carbohydrate derivative metabolic process
IEA
GO_REF:0000117 		ACCEPT
Summary: Electronic ARBA mapping to a very broad carbohydrate-derivative metabolism process. Correct but extremely general.
Reason: High-level parent; not incorrect but uninformative relative to the specific catabolic processes.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
oligosaccharide moieties from proteins and neutral glycolipids, or from
GO:0005515 protein binding
IPI
PMID:16698036
Crystallographic structure of human beta-hexosaminidase A: i... 		MARK AS OVER ANNOTATED
Summary: IPI protein-binding annotation from the Hex A crystal structure, capturing the HEXA-HEXB (alpha-beta) interaction. Bare 'protein binding' is uninformative; the biologically meaningful heterodimerization and complex membership are captured separately by GO:0046982 and GO:1905379.
Reason: Uninformative generic 'protein binding'; the specific HEXA-HEXB interaction is better represented by the heterodimerization activity and complex-membership annotations.
Supporting Evidence:
PMID:16698036
Hex A reveals an alphabeta heterodimer, with each subunit having a functional active site
GO:0005515 protein binding
IPI
PMID:28514442
Architecture of the human interactome defines protein commun... 		MARK AS OVER ANNOTATED
Summary: IPI protein-binding annotation from a large-scale interactome study (with/from HEXB). Bare 'protein binding' is uninformative for function.
Reason: Generic protein-binding from a high-throughput interactome; not an informative molecular function. The relevant HEXA-HEXB interaction is captured by GO:0046982 / GO:1905379.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
is a heterodimer composed of one subunit alpha and
GO:0005515 protein binding
IPI
PMID:33961781
Dual proteome-scale networks reveal cell-specific remodeling... 		MARK AS OVER ANNOTATED
Summary: IPI protein-binding annotation from a proteome-scale interactome network study (with/from HEXB). Bare 'protein binding' is uninformative.
Reason: Generic protein-binding from a high-throughput interactome; superseded for curation purposes by the specific heterodimerization/complex annotations.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
is a heterodimer composed of one subunit alpha and
GO:0030203 glycosaminoglycan metabolic process
IEA
GO_REF:0000107 		ACCEPT
Summary: Ensembl-orthology electronic transfer of glycosaminoglycan metabolic process from mouse Hexa. Consistent with the alpha-subunit role in degrading sulfated GAG fragments.
Reason: Correct process, corroborated by experimental evidence for GAG (dermatan/ keratan sulfate) turnover by Hex A.
Supporting Evidence:
PMID:6458607
keratan sulfate-derived oligosaccharides with beta-N-acetylhexosaminidase A analogously resulted in the liberation of N-acetylglucosamine-6-sulfate
GO:0004563 beta-N-acetylhexosaminidase activity
IDA
PMID:11707436
Physiological substrates for human lysosomal beta -hexosamin... 		ACCEPT
Summary: Direct assay of recombinant hexosaminidase (Hex S, the alpha-alpha homodimer) showing beta-hexosaminidase activity on multiple glycoconjugate substrates including sulfated GAG fragments and SM2. Confirms the alpha-subunit catalytic activity.
Reason: Experimental confirmation of the core molecular function of the alpha subunit.
Supporting Evidence:
PMID:11707436
Human lysosomal beta-hexosaminidases remove terminal beta-glycosidically bound
PMID:11707436
N-acetylhexosamine residues from a number of glycoconjugates
GO:0036021 endolysosome lumen
IC
PMID:11707436
Physiological substrates for human lysosomal beta -hexosamin... 		KEEP AS NON CORE
Summary: Curator inference (IC) that the enzyme acts in the endolysosome lumen, consistent with the acidic acid-hydrolase compartment. A more specific sibling of lysosomal lumen; both are legitimate, and the core lumen location is retained via GO:0043202.
Reason: Reasonable inferred compartment; endolysosome lumen refines the lumen site of action but the canonical/core term used here is lysosomal lumen.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
Lysosome
GO:0036021 endolysosome lumen
IC
PMID:27498570
Endolysosomes Are the Principal Intracellular Sites of Acid ... 		KEEP AS NON CORE
Summary: Curator inference from a study showing endolysosomes are the principal intracellular sites of acid-hydrolase activity, applied to HEXA (an acid hydrolase) via its ganglioside catabolic role. Reasonable but non-core.
Reason: The paper establishes endolysosomes as the acid-hydrolase-active compartment; inferring HEXA acts there is sound but the core lumen term used is lysosomal lumen.
Supporting Evidence:
PMID:27498570
endolysosomes are the principal organelles in which substrates are hydrolyzed
GO:0004563 beta-N-acetylhexosaminidase activity
TAS
Reactome:R-HSA-9035976 		ACCEPT
Summary: Reactome (TAS) assertion of beta-N-acetylhexosaminidase activity. The source reaction describes a defective HEXA variant in hyaluronan metabolism, but the molecular function assigned (beta-N-acetylhexosaminidase activity) is the correct wild-type activity.
Reason: Correct core molecular function; the enzyme cleaves terminal hexosamines from hyaluronan/GAG fragments in the lysosome.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
Hydrolyzes the non-reducing end N-acetyl-D-hexosamine
GO:0004563 beta-N-acetylhexosaminidase activity
IDA
PMID:9694901
A Pro504 --> Ser substitution in the beta-subunit of beta-he... 		ACCEPT
Summary: Biochemical characterization of Hex A (alpha-beta) showing GM2-ganglioside hydrolysis by the alpha active site. Direct evidence for beta-hexosaminidase activity of the alpha-containing enzyme.
Reason: Experimental confirmation of the core catalytic activity via GM2 hydrolysis assays.
Supporting Evidence:
PMID:9694901
the active site associated with the hydrolysis of
PMID:9694901
GM2 ganglioside, as well as part of the binding site for the
GO:0006689 ganglioside catabolic process
IDA
PMID:9694901
A Pro504 --> Ser substitution in the beta-subunit of beta-he... 		ACCEPT
Summary: Direct evidence that the alpha active site of Hex A hydrolyses GM2 ganglioside; a beta-Pro504Ser mutation selectively impairs this natural-substrate activity, causing chronic Sandhoff disease. Core ganglioside catabolism.
Reason: Experimental support for the alpha-specific GM2 catabolic process.
Supporting Evidence:
PMID:9694901
ganglioside-activator complex, is associated with the alpha-subunit
GO:0004563 beta-N-acetylhexosaminidase activity
EXP
PMID:11707436
Physiological substrates for human lysosomal beta -hexosamin... 		ACCEPT
Summary: Experimental (EXP) determination of the catalytic activity of the alpha subunit enzyme on physiological substrates. Duplicate evidence for the core MF.
Reason: Direct experimental confirmation of beta-N-acetylhexosaminidase activity.
Supporting Evidence:
PMID:11707436
Human lysosomal beta-hexosaminidases remove terminal beta-glycosidically bound
GO:0030203 glycosaminoglycan metabolic process
IDA
PMID:25645918
Human neutrophils secrete bioactive paucimannosidic proteins... 		ACCEPT
Summary: ComplexPortal IDA linking Hex A to glycosaminoglycan/glycan metabolism. Consistent with the alpha-subunit role in removing terminal hexosamines from GAG and glycan substrates.
Reason: Correct core process; corroborated by direct GAG-degradation evidence (dermatan/keratan sulfate).
Supporting Evidence:
PMID:11707436
substrates, sulfated GAG fragments, and the sulfated glycosphingolipid SM2
GO:0043202 lysosomal lumen
NAS
PMID:6458607
Liberation of N-acetylglucosamine-6-sulfate by human beta-N-... 		ACCEPT
Summary: Non-traceable-author-statement localization to lysosomal lumen (the site where Hex A degrades sulfated keratan-sulfate oligosaccharides). Core lumen localization.
Reason: Correct soluble-lumen localization of the acid hydrolase.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
Lysosome
GO:1905379 beta-N-acetylhexosaminidase complex
IPI
PMID:16698036
Crystallographic structure of human beta-hexosaminidase A: i... 		ACCEPT
Summary: HEXA is a subunit of the beta-N-acetylhexosaminidase complex (Hex A alpha-beta heterodimer), established by the crystal structure. Core complex membership.
Reason: Correct, structurally defined complex membership central to enzyme function.
Supporting Evidence:
PMID:16698036
Hex A reveals an alphabeta heterodimer, with each subunit having a functional active site
GO:0030203 glycosaminoglycan metabolic process
IDA
PMID:11707436
Physiological substrates for human lysosomal beta -hexosamin... 		ACCEPT
Summary: ComplexPortal IDA (from the Hex S physiological-substrate study) linking the alpha-subunit enzyme to glycosaminoglycan metabolism via degradation of sulfated GAG fragments and dermatan sulfate.
Reason: Directly supported core process; the enzyme degrades sulfated GAG fragments and dermatan-sulfate-derived glycans.
Supporting Evidence:
PMID:11707436
the anionic glycans were identified as products of incomplete dermatan
GO:1905379 beta-N-acetylhexosaminidase complex
IDA
PMID:11707436
Physiological substrates for human lysosomal beta -hexosamin... 		ACCEPT
Summary: ComplexPortal IDA placing the alpha subunit in the beta-N-acetylhexosaminidase complex, consistent with the alpha-alpha (Hex S) and alpha-beta (Hex A) dimers characterized in this study. Core complex membership.
Reason: Correct complex membership; the functional enzyme is an obligate dimer of hexosaminidase subunits.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
isozyme S (hexosaminidase S) is a homodimer of two alpha subunits
GO:0043202 lysosomal lumen
TAS
Reactome:R-HSA-1605595 		ACCEPT
Summary: Reactome (TAS) localization to lysosomal lumen for the GM2A:GM2 to GM2A:GM3 reaction catalyzed by Hex A. Core lumen localization.
Reason: Accurate soluble-lumen localization for the GM2-degradation reaction.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
Lysosome
GO:0043202 lysosomal lumen
TAS
Reactome:R-HSA-1605632 		ACCEPT
Summary: Reactome (TAS) localization to lysosomal lumen for a glycosphingolipid (Gb4Cer) degradation reaction. Core lumen localization.
Reason: Accurate soluble-lumen localization consistent with lysosomal acid-hydrolase biology.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
Lysosome
GO:0043202 lysosomal lumen
TAS
Reactome:R-HSA-1638053 		ACCEPT
Summary: Reactome (TAS) localization to lysosomal lumen for HEXA cleaving terminal GlcNAc from keratan sulfate. Core lumen localization.
Reason: Accurate soluble-lumen localization for keratan-sulfate degradation.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
Lysosome
GO:0043202 lysosomal lumen
TAS
Reactome:R-HSA-2105001 		ACCEPT
Summary: Reactome (TAS) localization to lysosomal lumen for HEXA cleaving terminal GalNAc from dermatan sulfate. Core lumen localization.
Reason: Accurate soluble-lumen localization for dermatan-sulfate degradation.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
Lysosome
GO:0043202 lysosomal lumen
TAS
Reactome:R-HSA-2162225 		ACCEPT
Summary: Reactome (TAS) localization to lysosomal lumen for HEXA cleaving terminal GlcNAc from small hyaluronan fragments. Core lumen localization.
Reason: Accurate soluble-lumen localization for hyaluronan-fragment degradation.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
Lysosome
GO:0043202 lysosomal lumen
TAS
Reactome:R-HSA-9840833 		ACCEPT
Summary: Reactome (TAS) localization to lysosomal lumen for the GM2A:GA2 to GM2A:LacCer reaction. Core lumen localization.
Reason: Accurate soluble-lumen localization consistent with glycosphingolipid catabolism.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
Lysosome
GO:0043202 lysosomal lumen
TAS
Reactome:R-HSA-9840884 		ACCEPT
Summary: Reactome (TAS) localization to lysosomal lumen for the bHEXA,bHEXS hydrolysis of GM2A:SM2. Core lumen localization.
Reason: Accurate soluble-lumen localization for SM2 (sulfated glycosphingolipid) degradation.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
Addition of GM2A stimulates the hydrolysis of
GO:0005576 extracellular region
IDA
PMID:33966596
CREG1 promotes lysosomal biogenesis and function. 		KEEP AS NON CORE
Summary: IDA extracellular-region localization from a CREG1 lysosomal-biogenesis study in which HEXA is used as a lysosomal/secreted hydrolase marker. A fraction of the enzyme is secreted, but this is a non-core location for a lysosomal enzyme.
Reason: Secreted fraction of a normally lysosomal hydrolase; retain but non-core.
Supporting Evidence:
PMID:33966596
CREG1 is an endosomal-lysosomal protein
GO:0004563 beta-N-acetylhexosaminidase activity
IDA
PMID:8123671
Classification of disorders of GM2 ganglioside hydrolysis us... 		ACCEPT
Summary: Direct assay of GM2-ganglioside hydrolysis (3H-GM2 substrate) distinguishing normal from Tay-Sachs/Sandhoff fibroblasts, evidencing the beta-hexosaminidase activity of the alpha-containing enzyme.
Reason: Experimental confirmation of the core catalytic activity.
Supporting Evidence:
PMID:8123671
Rates of GM2 ganglioside hydrolysis by fibroblasts from normal controls and
GO:0004563 beta-N-acetylhexosaminidase activity
IDA
PMID:8672428
Direct determination of the substrate specificity of the alp... 		ACCEPT
Summary: Direct determination of the alpha-active-site substrate specificity in heterodimeric Hex A, confirming beta-hexosaminidase activity of the alpha subunit.
Reason: Experimental confirmation of the core molecular function and its substrate-specificity in the heterodimer.
Supporting Evidence:
PMID:8672428
Heterodimeric hexosaminidase A (alpha beta) is the only isozyme
GO:0006689 ganglioside catabolic process
IDA
PMID:8123671
Classification of disorders of GM2 ganglioside hydrolysis us... 		ACCEPT
Summary: Direct GM2-hydrolysis assays in fibroblasts showing loss of GM2 degradation in Tay-Sachs (HEXA-deficient) cells, evidencing the alpha-subunit role in ganglioside catabolism.
Reason: Experimental support for the alpha-specific GM2 ganglioside catabolic process.
Supporting Evidence:
PMID:8123671
cell extracts from patients with Tay-Sachs
GO:0006689 ganglioside catabolic process
IDA
PMID:8672428
Direct determination of the substrate specificity of the alp... 		ACCEPT
Summary: Direct characterization showing the Hex A alpha-active site hydrolyses GM2 ganglioside in vivo with the GM2 activator protein. Core ganglioside catabolism.
Reason: Experimental support for the alpha-specific GM2 catabolic process.
Supporting Evidence:
PMID:8672428
that can hydrolyze GM2 ganglioside in vivo, requiring the presence of the GM2
GO:0043202 lysosomal lumen
TAS
Reactome:R-HSA-9035976 		ACCEPT
Summary: Reactome (TAS) localization to lysosomal lumen (from the defective-HEXA hyaluronan reaction). Core lumen localization; the location is correct irrespective of the defective-variant framing of the source reaction.
Reason: Accurate soluble-lumen localization of the enzyme.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
Lysosome
GO:0006024 glycosaminoglycan biosynthetic process
IDA
PMID:25645918
Human neutrophils secrete bioactive paucimannosidic proteins... 		MARK AS OVER ANNOTATED
Summary: IDA to a glycosaminoglycan BIOSYNTHETIC process from the neutrophil azurophil-granule paper. This mis-assigns the process direction - HEXA is a hydrolase that trims/degrades N-glycans (generating paucimannosidic structures), it does not synthesize glycosaminoglycans. The underlying activity is catabolic N-glycan trimming.
Reason: Wrong process direction (biosynthetic vs catabolic) for an experimental annotation; the actual activity is hydrolytic N-glycan trimming, captured by GO:0004563 and the catabolic GAG/glycan processes. Retained (not removed) per policy for experimental annotations, but flagged as over-/mis-annotated.
Supporting Evidence:
PMID:25645918
by trimming hybrid/complex type N-glycan intermediates with relative broad
GO:0008375 acetylglucosaminyltransferase activity
IDA
PMID:25645918
Human neutrophils secrete bioactive paucimannosidic proteins... 		MARK AS OVER ANNOTATED
Summary: IDA to acetylglucosaminyltransferase (glycosyltransferase) activity from the neutrophil azurophil-granule paper. This mis-classifies the enzyme - the paper shows Hex A generating paucimannosidic N-glycans by TRIMMING (hydrolysing) hybrid/ complex N-glycan intermediates, i.e. a hydrolase acting in the catabolic direction, not a transferase adding GlcNAc.
Reason: Wrong enzyme class for the assigned MF; HEXA is a GH20 hydrolase, not a glycosyltransferase. The observed activity is hydrolytic N-glycan trimming (GO:0004563). Retained (not removed) per policy for experimental annotations, but flagged as mis-/over-annotated.
Supporting Evidence:
PMID:25645918
displayed the capacity to generate paucimannosidic N-glycans
PMID:25645918
by trimming hybrid/complex type N-glycan intermediates with relative broad
GO:0042582 azurophil granule
IDA
PMID:25645918
Human neutrophils secrete bioactive paucimannosidic proteins... 		KEEP AS NON CORE
Summary: IDA localization to neutrophil azurophil granules, with immunocytochemical co-localization of beta-hexosaminidase A with the azurophilic marker MPO. A real but cell-type-specific, non-core location (azurophil granules are lysosome-related organelles).
Reason: Legitimate specialized localization in neutrophils; not the core (canonical lysosomal) site of action.
Supporting Evidence:
PMID:25645918
and the azurophilic marker MPO in human
GO:0070062 extracellular exosome
HDA
PMID:23533145
In-depth proteomic analyses of exosomes isolated from expres... 		KEEP AS NON CORE
Summary: High-throughput proteomic detection of HEXA in urinary prostatic-secretion exosomes. A mass-spectrometry co-purification, indicative of secreted/exosomal presence rather than a core functional location.
Reason: Proteomic detection in exosomes; a non-core, incidental extracellular location for a lysosomal enzyme.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
oligosaccharide moieties from proteins and neutral glycolipids, or from
GO:0016020 membrane
HDA
PMID:19946888
Defining the membrane proteome of NK cells. 		MARK AS OVER ANNOTATED
Summary: High-throughput detection in an NK-cell membrane-proteome study. HEXA is a soluble lumenal enzyme; its appearance in a membrane fraction reflects association with membranes/organelle co-purification, not integral membrane residence.
Reason: Non-specific 'membrane' from a high-throughput membrane-proteome dataset; HEXA is a soluble lysosomal enzyme, so integral-membrane localization is not supported.
Supporting Evidence:
file:human/HEXA/HEXA-uniprot.txt
Lysosome
GO:0046982 protein heterodimerization activity
IDA
PMID:6230359
Association of alpha- and beta-subunits during the biosynthe... 		ACCEPT
Summary: Direct biosynthetic study showing the alpha chain associates with the beta chain to form the mature alpha-beta heterodimer, an association required for catalytic activity and lysosomal transport. Informative molecular function underlying Hex A assembly.
Reason: Specific, informative heterodimerization activity (alpha-beta assembly), directly supported and biologically central.
Supporting Evidence:
PMID:6230359
association with beta-chains is necessary not only for acquisition of catalytic
PMID:6230359
activity but also for transport of alpha-chains to lysosomes

Core Functions

Lysosomal beta-N-acetylhexosaminidase (alpha subunit of hexosaminidase A, the alpha-beta heterodimer) that hydrolyses terminal non-reducing beta-linked N-acetyl-D-hexosamine residues from glycoconjugates; with the GM2-activator protein the alpha active site degrades GM2 ganglioside (GalNAc removal, GM2 -> GM3).

Molecular Function:
beta-N-acetylhexosaminidase activity
Directly Involved In:
ganglioside catabolic process glycosaminoglycan metabolic process
Cellular Locations:
lysosomal lumen lysosome
In Complex:
beta-N-acetylhexosaminidase complex
Supporting Evidence:
  • file:human/HEXA/HEXA-uniprot.txt
    Hydrolyzes the non-reducing end N-acetyl-D-hexosamine
  • PMID:16698036
    Only the alpha-subunit active site can hydrolyze GM2 gangliosides
  • PMID:8672428
    that can hydrolyze GM2 ganglioside in vivo, requiring the presence of the GM2
  • PMID:6458607
    keratan sulfate-derived oligosaccharides with beta-N-acetylhexosaminidase A analogously resulted in the liberation of N-acetylglucosamine-6-sulfate

References

GO_REF:0000002
Gene Ontology annotation through association of InterPro records with GO terms
GO_REF:0000033
Annotation inferences using phylogenetic trees
GO_REF:0000044
Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt
GO_REF:0000107
Automatic transfer of experimentally verified manual GO annotation data to orthologs using Ensembl Compara
GO_REF:0000117
Electronic Gene Ontology annotations created by ARBA machine learning models
GO_REF:0000120
Combined Automated Annotation using Multiple IEA Methods
file:human/HEXA/HEXA-uniprot.txt
HEXA UniProtKB record (P06865)
PMID:11707436
Physiological substrates for human lysosomal beta -hexosaminidase S.
PMID:16698036
Crystallographic structure of human beta-hexosaminidase A: interpretation of Tay-Sachs mutations and loss of GM2 ganglioside hydrolysis.
PMID:19946888
Defining the membrane proteome of NK cells.
PMID:23533145
In-depth proteomic analyses of exosomes isolated from expressed prostatic secretions in urine.
PMID:25645918
Human neutrophils secrete bioactive paucimannosidic proteins from azurophilic granules into pathogen-infected sputum.
PMID:27498570
Endolysosomes Are the Principal Intracellular Sites of Acid Hydrolase Activity.
PMID:28514442
Architecture of the human interactome defines protein communities and disease networks.
PMID:33961781
Dual proteome-scale networks reveal cell-specific remodeling of the human interactome.
PMID:33966596
CREG1 promotes lysosomal biogenesis and function.
PMID:6230359
Association of alpha- and beta-subunits during the biosynthesis of beta-hexosaminidase in cultured human fibroblasts.
PMID:6458607
Liberation of N-acetylglucosamine-6-sulfate by human beta-N-acetylhexosaminidase A.
PMID:8123671
Classification of disorders of GM2 ganglioside hydrolysis using 3H-GM2 as substrate.
PMID:8672428
Direct determination of the substrate specificity of the alpha-active site in heterodimeric beta-hexosaminidase A.
PMID:9694901
A Pro504 --> Ser substitution in the beta-subunit of beta-hexosaminidase A inhibits alpha-subunit hydrolysis of GM2 ganglioside, resulting in chronic Sandhoff disease.
Reactome:R-HSA-1605595
bHEXA hydrolyzes GM2A:GM2 to GM2A:GM3
Reactome:R-HSA-1605632
bHEXA,bHEXB hydrolyze PSAP(195-273):Gb4Cer:PE
Reactome:R-HSA-1638053
HEXA cleaves the terminal GlcNAc from keratan sulfate
Reactome:R-HSA-2105001
HEXA cleaves the terminal GalNAc from DS
Reactome:R-HSA-2162225
HEXA cleaves the terminal GlcNAc from small HA fragments
Reactome:R-HSA-9035976
Defective HEXA does not cleave the terminall GalNAc from small HA fragments
Reactome:R-HSA-9840833
bHEXA,bHEXB hydrolyze GM2A:GA2 to GM2A:LacCer
Reactome:R-HSA-9840884
bHEXA,bHEXS hydrolyze GM2A:SM2

Suggested Questions for Experts

Q: Beyond GM2 ganglioside, dermatan sulfate and keratan sulfate, which glycoconjugate substrates in vivo depend specifically on the HEXA alpha active site (as opposed to the beta active site of HEXB)?

Q: To what extent do secreted/exosomal and neutrophil azurophil-granule pools of hexosaminidase A have physiological (non-lysosomal) roles?

Suggested Experiments

Experiment: Substrate-resolved lysosomal glycomics in HEXA-null versus HEXB-null cells to define the alpha-subunit-specific substrate repertoire in vivo.

Experiment: Structure-guided mutagenesis of the alpha-specific loop and Arg424 to dissect GM2A-dependent GM2 recognition versus general hexosaminidase activity.

📚 Additional Documentation

Notes

(HEXA-notes.md)

HEXA (Beta-hexosaminidase subunit alpha, UniProtKB:P06865) — review notes

Summary of biology (grounded in UniProt P06865, GOA, cached publications)

HEXA encodes the alpha subunit of lysosomal beta-hexosaminidase, a glycoside
hydrolase family 20 (GH20) enzyme (EC 3.2.1.52). Three isozymes exist, defined by
subunit composition [file:human/HEXA/HEXA-uniprot.txt "isozyme A ... is a heterodimer
composed of one subunit alpha and one subunit beta"; "isozyme S (hexosaminidase S) is
a homodimer of two alpha subunits"]:
- Hex A = alpha-beta heterodimer (HEXA + HEXB)
- Hex B = beta-beta homodimer (HEXB only)
- Hex S = alpha-alpha homodimer (HEXA only)

The enzyme hydrolyses terminal non-reducing beta-linked N-acetyl-D-hexosamine
(beta-GalNAc/GlcNAc, including sulfated hexosamine) residues from glycoconjugates
[file:human/HEXA/HEXA-uniprot.txt "Hydrolyzes the non-reducing end N-acetyl-D-hexosamine
and/or sulfated N-acetyl-D-hexosamine of glycoconjugates"].

The alpha-subunit active site is uniquely able, together with the GM2-activator
protein (GM2A), to hydrolyse the GM2 ganglioside (removing terminal GalNAc to give
GM3). Only Hex A (which contains alpha) does this in vivo
[PMID:16698036 "Only the alpha-subunit active site can hydrolyze GM2 gangliosides";
PMID:8672428 "Heterodimeric hexosaminidase A (alpha beta) is the only isozyme that can
hydrolyze GM2 ganglioside in vivo, requiring the presence of the GM2 activator protein"].
The alpha active site preferentially handles negatively charged/sulfated substrates,
so Hex A/Hex S also degrade sulfated glycosaminoglycan (GAG) fragments (dermatan
sulfate, keratan sulfate) and the sulfated glycosphingolipid SM2
[PMID:11707436 "active on water-soluble and amphiphilic glycoconjugates including
artificial substrates, sulfated GAG fragments, and the sulfated glycosphingolipid SM2";
PMID:6458607 "Incubation of keratan sulfate-derived oligosaccharides with
beta-N-acetylhexosaminidase A analogously resulted in the liberation of
N-acetylglucosamine-6-sulfate"].

Localisation: lysosome / lysosomal lumen (acidic acid-hydrolase compartment)
[file:human/HEXA/HEXA-uniprot.txt "Lysosome"]. The alpha chain requires association with
the beta chain for catalytic maturation and lysosomal transport
PMID:6230359.

Disease: loss of HEXA activity causes GM2-gangliosidosis type 1 (Tay-Sachs disease),
an autosomal-recessive lysosomal storage disorder with neuronal GM2 accumulation
[file:human/HEXA/HEXA-uniprot.txt "GM2-gangliosidosis 1 (GM2G1)"; "accumulation of GM2"].

Core functions selected

  • MF: GO:0004563 beta-N-acetylhexosaminidase activity (exact GOA term/label; EC 3.2.1.52)
  • BP: GO:0006689 ganglioside catabolic process (GM2 degradation; alpha-specific)
  • BP: GO:0030203 glycosaminoglycan metabolic process (dermatan/keratan sulfate GAG turnover)
  • CC: GO:0043202 lysosomal lumen; GO:0005764 lysosome
  • Complex (in_complex): GO:1905379 beta-N-acetylhexosaminidase complex (Hex A alpha-beta)

Notable curation decisions

  • GO:0008375 acetylglucosaminyltransferase activity (IEA ARBA + IDA PMID:25645918):
    biologically wrong direction — HEXA is a hydrolase (GH20), not a glycosyltransferase.
    The PMID:25645918 azurophil-granule paper describes N-glycan trimming (hydrolysis),
    not sugar transfer. REMOVE the electronic ARBA inference; the experimental IDA is
    marked MARK_AS_OVER_ANNOTATED (do not REMOVE an experimental annotation) — the
    underlying activity is hydrolytic N-glycan trimming, better captured by GO:0004563.
  • GO:0006024 glycosaminoglycan biosynthetic process (IDA PMID:25645918): mis-assigned
    process direction — the paper is about catabolic N-glycan trimming, not GAG
    biosynthesis. Experimental → MARK_AS_OVER_ANNOTATED (retain hydrolytic/catabolic
    reading via GO:0004563 / GO:0030203).
  • GO:0005515 protein binding (3× IPI, all HEXA-HEXB IntAct): uninformative bare
    protein-binding; MARK_AS_OVER_ANNOTATED. The biologically meaningful heterodimerization
    is separately captured by GO:0046982 (IDA) and GO:1905379 complex membership.
  • Extracellular region / azurophil granule / exosome / membrane: peripheral secretion/
    proteomics detections of a normally lysosomal enzyme → KEEP_AS_NON_CORE.
  • Reactome R-HSA-9035976 "Defective HEXA does not cleave..." (TAS): a defective-variant
    reaction; the enables GO:0004563 annotation derived from it is retained (activity is
    correct for wild-type) but flagged in reason.

📄 View Raw YAML

 
id: P06865
gene_symbol: HEXA
product_type: PROTEIN
status: INITIALIZED
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: HEXA encodes the alpha subunit of lysosomal beta-hexosaminidase, a
  glycoside hydrolase family 20 (GH20) enzyme (EC 3.2.1.52). With the beta subunit
  (HEXB) it forms beta-hexosaminidase A, the alpha-beta heterodimer; the beta-beta
  homodimer is hexosaminidase B and the alpha-alpha homodimer is hexosaminidase S.
  The enzyme hydrolyses terminal non-reducing beta-linked N-acetyl-D-hexosamine
  (beta-GalNAc/GlcNAc, including sulfated hexosamine) residues from a range of
  glycoconjugates. The alpha-subunit active site is uniquely able, together with the
  GM2-activator protein (GM2A), to hydrolyse the GM2 ganglioside (removing the terminal
  GalNAc to give GM3); only hexosaminidase A performs this reaction in vivo. Because
  the alpha active site accepts negatively charged/sulfated substrates, hexosaminidase
  A/S also degrade sulfated glycosaminoglycan fragments (dermatan sulfate, keratan
  sulfate) and other glycoconjugates such as the sulfated glycosphingolipid SM2. The
  enzyme acts in the lysosome / lysosomal lumen. Loss of HEXA activity causes
  GM2-gangliosidosis type 1 (Tay-Sachs disease), an autosomal-recessive lysosomal
  storage disease characterised by neuronal accumulation of GM2 ganglioside.
alternative_products:
- name: '1'
  id: P06865-1
- name: '2'
  id: P06865-2
  sequence_note: VSP_056657, VSP_056658, VSP_056659
existing_annotations:
- term:
    id: GO:0004563
    label: beta-N-acetylhexosaminidase activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  review:
    summary: Phylogenetic (IBA) propagation of the family-defining beta-N-acetylhexosaminidase
      activity. This is the exact molecular function of the HEXA alpha subunit and the
      core catalytic activity of the enzyme.
    action: ACCEPT
    reason: Correct core molecular function, matching the UniProt catalytic activity
      (EC 3.2.1.52) and multiple independent experimental annotations.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: Hydrolyzes the non-reducing end N-acetyl-D-hexosamine
- term:
    id: GO:0005576
    label: extracellular region
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: IBA propagation of an extracellular-region location. HEXA is fundamentally
      a lysosomal enzyme; a fraction is secreted (precursor alpha-beta complexes are
      secreted), and the enzyme is detected extracellularly, but this is not its core
      site of action.
    action: KEEP_AS_NON_CORE
    reason: Peripheral/secreted localization of a normally lysosomal hydrolase; retain
      but not as a core location.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: Lysosome
- term:
    id: GO:0005764
    label: lysosome
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: IBA propagation of lysosomal localization, the canonical site of action of
      beta-hexosaminidase A/S. This is a core cellular component.
    action: ACCEPT
    reason: Correct core localization; matches UniProt subcellular location and the
      acid-hydrolase biology of the enzyme.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: Lysosome
- term:
    id: GO:0030203
    label: glycosaminoglycan metabolic process
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: IBA propagation of glycosaminoglycan metabolism. The alpha active site
      removes terminal (sulfated) hexosamines from GAG fragments such as dermatan
      sulfate and keratan sulfate, so HEXA participates in lysosomal GAG catabolism.
    action: ACCEPT
    reason: Well supported core process; the alpha/Hex A active site degrades sulfated
      GAG fragments (dermatan/keratan sulfate).
    supported_by:
    - reference_id: PMID:11707436
      supporting_text: active on water-soluble and amphiphilic glycoconjugates including
        artificial substrates, sulfated GAG fragments, and the sulfated glycosphingolipid
        SM2
    - reference_id: PMID:6458607
      supporting_text: keratan sulfate-derived oligosaccharides with beta-N-acetylhexosaminidase
        A analogously resulted in the liberation of N-acetylglucosamine-6-sulfate
- term:
    id: GO:0006689
    label: ganglioside catabolic process
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: IBA propagation of ganglioside catabolism. The alpha subunit, within Hex A
      and together with GM2A, is uniquely responsible for GM2 ganglioside degradation.
      This is a core biological process and the process whose failure causes Tay-Sachs
      disease.
    action: ACCEPT
    reason: Core, alpha-specific process; only Hex A (containing alpha) degrades GM2 in
      vivo.
    supported_by:
    - reference_id: PMID:16698036
      supporting_text: Only the alpha-subunit active site can hydrolyze GM2 gangliosides
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: Only the isozyme A is responsible for the
- term:
    id: GO:0004553
    label: hydrolase activity, hydrolyzing O-glycosyl compounds
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: InterPro2GO electronic mapping to the parent O-glycosyl hydrolase activity.
      This is a correct but more general parent of the specific GO:0004563
      beta-N-acetylhexosaminidase activity.
    action: ACCEPT
    reason: Correct (if general) parent term; consistent with the GH20 glycosidase
      activity and not misleading.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: Belongs to the glycosyl hydrolase 20 family
- term:
    id: GO:0004563
    label: beta-N-acetylhexosaminidase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  review:
    summary: Electronic (ARBA/InterPro/EC) assignment of the family-defining
      beta-N-acetylhexosaminidase activity (EC 3.2.1.52), consistent with the
      experimental catalytic activity.
    action: ACCEPT
    reason: Correct core molecular function derived from EC 3.2.1.52 and family
      membership.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: Hydrolyzes the non-reducing end N-acetyl-D-hexosamine
- term:
    id: GO:0005764
    label: lysosome
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: Electronic mapping from the UniProt subcellular location (Lysosome) keyword.
      Correct core localization.
    action: ACCEPT
    reason: Matches the curated UniProt subcellular location and lysosomal biology.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: Lysosome
- term:
    id: GO:0005975
    label: carbohydrate metabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: involved_in
  review:
    summary: InterPro2GO electronic mapping to a broad carbohydrate-metabolism process.
      Correct but very general parent of the specific glycoconjugate/GAG/ganglioside
      catabolic processes.
    action: ACCEPT
    reason: Broad but not incorrect; a high-level parent of the specific catabolic
      processes captured elsewhere.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: oligosaccharide moieties from proteins and neutral glycolipids, or from
- term:
    id: GO:0008375
    label: acetylglucosaminyltransferase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  qualifier: enables
  review:
    summary: Electronic ARBA assignment of a glycosyltransferase (acetylglucosaminyltransferase)
      activity. This is biologically incorrect - HEXA is a GH20 glycoside hydrolase
      (EC 3.2.1.52) that removes terminal hexosamines by hydrolysis, not a transferase
      that adds GlcNAc. The transferase reading likely arises from misinterpreting
      N-glycan trimming reports as sugar transfer.
    action: REMOVE
    reason: Wrong enzyme class for an electronic inference; HEXA is a hydrolase, not a
      glycosyltransferase. This ARBA mapping contradicts the well-established catalytic
      activity and family assignment.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: Belongs to the glycosyl hydrolase 20 family
- term:
    id: GO:0016042
    label: lipid catabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  qualifier: involved_in
  review:
    summary: Electronic ARBA mapping to lipid catabolism. This is a reasonable broad
      parent given the role in glycosphingolipid (ganglioside GM2, SM2) degradation.
    action: ACCEPT
    reason: Correct high-level parent of glycosphingolipid/ganglioside catabolism;
      consistent with GM2 and SM2 degradation.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: degradation of GM2 gangliosides in the presence of GM2A
- term:
    id: GO:0042582
    label: azurophil granule
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  qualifier: located_in
  review:
    summary: Electronic ARBA mapping to azurophil granule, mirroring the experimental
      IDA (PMID:25645918) that detected azurophilic-granule-resident beta-hexosaminidase A
      in neutrophils. A real but non-core, cell-type-specific location.
    action: KEEP_AS_NON_CORE
    reason: Neutrophil azurophil granules are lysosome-related organelles; a legitimate
      but specialized, non-core location for this normally lysosomal enzyme.
    supported_by:
    - reference_id: PMID:25645918
      supporting_text: azurophilic granule-resident
- term:
    id: GO:0043202
    label: lysosomal lumen
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  qualifier: located_in
  review:
    summary: Electronic ARBA mapping to lysosomal lumen, the precise compartment where
      the soluble acid hydrolase acts. Core localization.
    action: ACCEPT
    reason: Accurate soluble-lumen localization consistent with UniProt and Reactome.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: Lysosome
- term:
    id: GO:1901135
    label: carbohydrate derivative metabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  qualifier: involved_in
  review:
    summary: Electronic ARBA mapping to a very broad carbohydrate-derivative metabolism
      process. Correct but extremely general.
    action: ACCEPT
    reason: High-level parent; not incorrect but uninformative relative to the specific
      catabolic processes.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: oligosaccharide moieties from proteins and neutral glycolipids, or from
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:16698036
  qualifier: enables
  review:
    summary: IPI protein-binding annotation from the Hex A crystal structure, capturing
      the HEXA-HEXB (alpha-beta) interaction. Bare 'protein binding' is uninformative;
      the biologically meaningful heterodimerization and complex membership are captured
      separately by GO:0046982 and GO:1905379.
    action: MARK_AS_OVER_ANNOTATED
    reason: Uninformative generic 'protein binding'; the specific HEXA-HEXB interaction
      is better represented by the heterodimerization activity and complex-membership
      annotations.
    supported_by:
    - reference_id: PMID:16698036
      supporting_text: Hex A reveals an alphabeta heterodimer, with each subunit having a functional
        active site
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:28514442
  qualifier: enables
  review:
    summary: IPI protein-binding annotation from a large-scale interactome study
      (with/from HEXB). Bare 'protein binding' is uninformative for function.
    action: MARK_AS_OVER_ANNOTATED
    reason: Generic protein-binding from a high-throughput interactome; not an
      informative molecular function. The relevant HEXA-HEXB interaction is captured by
      GO:0046982 / GO:1905379.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: is a heterodimer composed of one subunit alpha and
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:33961781
  qualifier: enables
  review:
    summary: IPI protein-binding annotation from a proteome-scale interactome network
      study (with/from HEXB). Bare 'protein binding' is uninformative.
    action: MARK_AS_OVER_ANNOTATED
    reason: Generic protein-binding from a high-throughput interactome; superseded for
      curation purposes by the specific heterodimerization/complex annotations.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: is a heterodimer composed of one subunit alpha and
- term:
    id: GO:0030203
    label: glycosaminoglycan metabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: Ensembl-orthology electronic transfer of glycosaminoglycan metabolic
      process from mouse Hexa. Consistent with the alpha-subunit role in degrading
      sulfated GAG fragments.
    action: ACCEPT
    reason: Correct process, corroborated by experimental evidence for GAG (dermatan/
      keratan sulfate) turnover by Hex A.
    supported_by:
    - reference_id: PMID:6458607
      supporting_text: keratan sulfate-derived oligosaccharides with beta-N-acetylhexosaminidase
        A analogously resulted in the liberation of N-acetylglucosamine-6-sulfate
- term:
    id: GO:0004563
    label: beta-N-acetylhexosaminidase activity
  evidence_type: IDA
  original_reference_id: PMID:11707436
  qualifier: enables
  review:
    summary: Direct assay of recombinant hexosaminidase (Hex S, the alpha-alpha
      homodimer) showing beta-hexosaminidase activity on multiple glycoconjugate
      substrates including sulfated GAG fragments and SM2. Confirms the alpha-subunit
      catalytic activity.
    action: ACCEPT
    reason: Experimental confirmation of the core molecular function of the alpha
      subunit.
    supported_by:
    - reference_id: PMID:11707436
      supporting_text: Human lysosomal beta-hexosaminidases remove terminal beta-glycosidically bound
    - reference_id: PMID:11707436
      supporting_text: N-acetylhexosamine residues from a number of glycoconjugates
- term:
    id: GO:0036021
    label: endolysosome lumen
  evidence_type: IC
  original_reference_id: PMID:11707436
  qualifier: is_active_in
  review:
    summary: Curator inference (IC) that the enzyme acts in the endolysosome lumen,
      consistent with the acidic acid-hydrolase compartment. A more specific sibling of
      lysosomal lumen; both are legitimate, and the core lumen location is retained via
      GO:0043202.
    action: KEEP_AS_NON_CORE
    reason: Reasonable inferred compartment; endolysosome lumen refines the lumen site
      of action but the canonical/core term used here is lysosomal lumen.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: Lysosome
- term:
    id: GO:0036021
    label: endolysosome lumen
  evidence_type: IC
  original_reference_id: PMID:27498570
  qualifier: is_active_in
  review:
    summary: Curator inference from a study showing endolysosomes are the principal
      intracellular sites of acid-hydrolase activity, applied to HEXA (an acid
      hydrolase) via its ganglioside catabolic role. Reasonable but non-core.
    action: KEEP_AS_NON_CORE
    reason: The paper establishes endolysosomes as the acid-hydrolase-active compartment;
      inferring HEXA acts there is sound but the core lumen term used is lysosomal lumen.
    supported_by:
    - reference_id: PMID:27498570
      supporting_text: endolysosomes are the principal organelles in which substrates are hydrolyzed
- term:
    id: GO:0004563
    label: beta-N-acetylhexosaminidase activity
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9035976
  qualifier: enables
  review:
    summary: Reactome (TAS) assertion of beta-N-acetylhexosaminidase activity. The
      source reaction describes a defective HEXA variant in hyaluronan metabolism, but
      the molecular function assigned (beta-N-acetylhexosaminidase activity) is the
      correct wild-type activity.
    action: ACCEPT
    reason: Correct core molecular function; the enzyme cleaves terminal hexosamines
      from hyaluronan/GAG fragments in the lysosome.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: Hydrolyzes the non-reducing end N-acetyl-D-hexosamine
- term:
    id: GO:0004563
    label: beta-N-acetylhexosaminidase activity
  evidence_type: IDA
  original_reference_id: PMID:9694901
  qualifier: enables
  review:
    summary: Biochemical characterization of Hex A (alpha-beta) showing GM2-ganglioside
      hydrolysis by the alpha active site. Direct evidence for beta-hexosaminidase
      activity of the alpha-containing enzyme.
    action: ACCEPT
    reason: Experimental confirmation of the core catalytic activity via GM2 hydrolysis
      assays.
    supported_by:
    - reference_id: PMID:9694901
      supporting_text: the active site associated with the hydrolysis of
    - reference_id: PMID:9694901
      supporting_text: GM2 ganglioside, as well as part of the binding site for the
- term:
    id: GO:0006689
    label: ganglioside catabolic process
  evidence_type: IDA
  original_reference_id: PMID:9694901
  qualifier: involved_in
  review:
    summary: Direct evidence that the alpha active site of Hex A hydrolyses GM2
      ganglioside; a beta-Pro504Ser mutation selectively impairs this natural-substrate
      activity, causing chronic Sandhoff disease. Core ganglioside catabolism.
    action: ACCEPT
    reason: Experimental support for the alpha-specific GM2 catabolic process.
    supported_by:
    - reference_id: PMID:9694901
      supporting_text: ganglioside-activator complex, is associated with the alpha-subunit
- term:
    id: GO:0004563
    label: beta-N-acetylhexosaminidase activity
  evidence_type: EXP
  original_reference_id: PMID:11707436
  qualifier: enables
  review:
    summary: Experimental (EXP) determination of the catalytic activity of the alpha
      subunit enzyme on physiological substrates. Duplicate evidence for the core MF.
    action: ACCEPT
    reason: Direct experimental confirmation of beta-N-acetylhexosaminidase activity.
    supported_by:
    - reference_id: PMID:11707436
      supporting_text: Human lysosomal beta-hexosaminidases remove terminal beta-glycosidically bound
- term:
    id: GO:0030203
    label: glycosaminoglycan metabolic process
  evidence_type: IDA
  original_reference_id: PMID:25645918
  qualifier: involved_in
  review:
    summary: ComplexPortal IDA linking Hex A to glycosaminoglycan/glycan metabolism.
      Consistent with the alpha-subunit role in removing terminal hexosamines from GAG
      and glycan substrates.
    action: ACCEPT
    reason: Correct core process; corroborated by direct GAG-degradation evidence
      (dermatan/keratan sulfate).
    supported_by:
    - reference_id: PMID:11707436
      supporting_text: substrates, sulfated GAG fragments, and the sulfated glycosphingolipid SM2
- term:
    id: GO:0043202
    label: lysosomal lumen
  evidence_type: NAS
  original_reference_id: PMID:6458607
  qualifier: located_in
  review:
    summary: Non-traceable-author-statement localization to lysosomal lumen (the site
      where Hex A degrades sulfated keratan-sulfate oligosaccharides). Core lumen
      localization.
    action: ACCEPT
    reason: Correct soluble-lumen localization of the acid hydrolase.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: Lysosome
- term:
    id: GO:1905379
    label: beta-N-acetylhexosaminidase complex
  evidence_type: IPI
  original_reference_id: PMID:16698036
  qualifier: part_of
  review:
    summary: HEXA is a subunit of the beta-N-acetylhexosaminidase complex (Hex A
      alpha-beta heterodimer), established by the crystal structure. Core complex
      membership.
    action: ACCEPT
    reason: Correct, structurally defined complex membership central to enzyme function.
    supported_by:
    - reference_id: PMID:16698036
      supporting_text: Hex A reveals an alphabeta heterodimer, with each subunit having a functional
        active site
- term:
    id: GO:0030203
    label: glycosaminoglycan metabolic process
  evidence_type: IDA
  original_reference_id: PMID:11707436
  qualifier: involved_in
  review:
    summary: ComplexPortal IDA (from the Hex S physiological-substrate study) linking the
      alpha-subunit enzyme to glycosaminoglycan metabolism via degradation of sulfated
      GAG fragments and dermatan sulfate.
    action: ACCEPT
    reason: Directly supported core process; the enzyme degrades sulfated GAG fragments
      and dermatan-sulfate-derived glycans.
    supported_by:
    - reference_id: PMID:11707436
      supporting_text: the anionic glycans were identified as products of incomplete dermatan
- term:
    id: GO:1905379
    label: beta-N-acetylhexosaminidase complex
  evidence_type: IDA
  original_reference_id: PMID:11707436
  qualifier: part_of
  review:
    summary: ComplexPortal IDA placing the alpha subunit in the beta-N-acetylhexosaminidase
      complex, consistent with the alpha-alpha (Hex S) and alpha-beta (Hex A) dimers
      characterized in this study. Core complex membership.
    action: ACCEPT
    reason: Correct complex membership; the functional enzyme is an obligate dimer of
      hexosaminidase subunits.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: isozyme S (hexosaminidase S) is a homodimer of two alpha subunits
- term:
    id: GO:0043202
    label: lysosomal lumen
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-1605595
  qualifier: located_in
  review:
    summary: Reactome (TAS) localization to lysosomal lumen for the GM2A:GM2 to GM2A:GM3
      reaction catalyzed by Hex A. Core lumen localization.
    action: ACCEPT
    reason: Accurate soluble-lumen localization for the GM2-degradation reaction.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: Lysosome
- term:
    id: GO:0043202
    label: lysosomal lumen
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-1605632
  qualifier: located_in
  review:
    summary: Reactome (TAS) localization to lysosomal lumen for a glycosphingolipid
      (Gb4Cer) degradation reaction. Core lumen localization.
    action: ACCEPT
    reason: Accurate soluble-lumen localization consistent with lysosomal acid-hydrolase
      biology.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: Lysosome
- term:
    id: GO:0043202
    label: lysosomal lumen
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-1638053
  qualifier: located_in
  review:
    summary: Reactome (TAS) localization to lysosomal lumen for HEXA cleaving terminal
      GlcNAc from keratan sulfate. Core lumen localization.
    action: ACCEPT
    reason: Accurate soluble-lumen localization for keratan-sulfate degradation.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: Lysosome
- term:
    id: GO:0043202
    label: lysosomal lumen
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-2105001
  qualifier: located_in
  review:
    summary: Reactome (TAS) localization to lysosomal lumen for HEXA cleaving terminal
      GalNAc from dermatan sulfate. Core lumen localization.
    action: ACCEPT
    reason: Accurate soluble-lumen localization for dermatan-sulfate degradation.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: Lysosome
- term:
    id: GO:0043202
    label: lysosomal lumen
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-2162225
  qualifier: located_in
  review:
    summary: Reactome (TAS) localization to lysosomal lumen for HEXA cleaving terminal
      GlcNAc from small hyaluronan fragments. Core lumen localization.
    action: ACCEPT
    reason: Accurate soluble-lumen localization for hyaluronan-fragment degradation.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: Lysosome
- term:
    id: GO:0043202
    label: lysosomal lumen
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9840833
  qualifier: located_in
  review:
    summary: Reactome (TAS) localization to lysosomal lumen for the GM2A:GA2 to
      GM2A:LacCer reaction. Core lumen localization.
    action: ACCEPT
    reason: Accurate soluble-lumen localization consistent with glycosphingolipid
      catabolism.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: Lysosome
- term:
    id: GO:0043202
    label: lysosomal lumen
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9840884
  qualifier: located_in
  review:
    summary: Reactome (TAS) localization to lysosomal lumen for the bHEXA,bHEXS
      hydrolysis of GM2A:SM2. Core lumen localization.
    action: ACCEPT
    reason: Accurate soluble-lumen localization for SM2 (sulfated glycosphingolipid)
      degradation.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: Addition of GM2A stimulates the hydrolysis of
- term:
    id: GO:0005576
    label: extracellular region
  evidence_type: IDA
  original_reference_id: PMID:33966596
  qualifier: located_in
  review:
    summary: IDA extracellular-region localization from a CREG1 lysosomal-biogenesis
      study in which HEXA is used as a lysosomal/secreted hydrolase marker. A fraction
      of the enzyme is secreted, but this is a non-core location for a lysosomal enzyme.
    action: KEEP_AS_NON_CORE
    reason: Secreted fraction of a normally lysosomal hydrolase; retain but non-core.
    supported_by:
    - reference_id: PMID:33966596
      supporting_text: CREG1 is an endosomal-lysosomal protein
- term:
    id: GO:0004563
    label: beta-N-acetylhexosaminidase activity
  evidence_type: IDA
  original_reference_id: PMID:8123671
  qualifier: enables
  review:
    summary: Direct assay of GM2-ganglioside hydrolysis (3H-GM2 substrate) distinguishing
      normal from Tay-Sachs/Sandhoff fibroblasts, evidencing the beta-hexosaminidase
      activity of the alpha-containing enzyme.
    action: ACCEPT
    reason: Experimental confirmation of the core catalytic activity.
    supported_by:
    - reference_id: PMID:8123671
      supporting_text: Rates of GM2 ganglioside hydrolysis by fibroblasts from normal controls and
- term:
    id: GO:0004563
    label: beta-N-acetylhexosaminidase activity
  evidence_type: IDA
  original_reference_id: PMID:8672428
  qualifier: enables
  review:
    summary: Direct determination of the alpha-active-site substrate specificity in
      heterodimeric Hex A, confirming beta-hexosaminidase activity of the alpha subunit.
    action: ACCEPT
    reason: Experimental confirmation of the core molecular function and its
      substrate-specificity in the heterodimer.
    supported_by:
    - reference_id: PMID:8672428
      supporting_text: Heterodimeric hexosaminidase A (alpha beta) is the only isozyme
- term:
    id: GO:0006689
    label: ganglioside catabolic process
  evidence_type: IDA
  original_reference_id: PMID:8123671
  qualifier: involved_in
  review:
    summary: Direct GM2-hydrolysis assays in fibroblasts showing loss of GM2 degradation
      in Tay-Sachs (HEXA-deficient) cells, evidencing the alpha-subunit role in
      ganglioside catabolism.
    action: ACCEPT
    reason: Experimental support for the alpha-specific GM2 ganglioside catabolic
      process.
    supported_by:
    - reference_id: PMID:8123671
      supporting_text: cell extracts from patients with Tay-Sachs
- term:
    id: GO:0006689
    label: ganglioside catabolic process
  evidence_type: IDA
  original_reference_id: PMID:8672428
  qualifier: involved_in
  review:
    summary: Direct characterization showing the Hex A alpha-active site hydrolyses GM2
      ganglioside in vivo with the GM2 activator protein. Core ganglioside catabolism.
    action: ACCEPT
    reason: Experimental support for the alpha-specific GM2 catabolic process.
    supported_by:
    - reference_id: PMID:8672428
      supporting_text: that can hydrolyze GM2 ganglioside in vivo, requiring the presence of the GM2
- term:
    id: GO:0043202
    label: lysosomal lumen
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9035976
  qualifier: located_in
  review:
    summary: Reactome (TAS) localization to lysosomal lumen (from the defective-HEXA
      hyaluronan reaction). Core lumen localization; the location is correct
      irrespective of the defective-variant framing of the source reaction.
    action: ACCEPT
    reason: Accurate soluble-lumen localization of the enzyme.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: Lysosome
- term:
    id: GO:0006024
    label: glycosaminoglycan biosynthetic process
  evidence_type: IDA
  original_reference_id: PMID:25645918
  qualifier: involved_in
  review:
    summary: IDA to a glycosaminoglycan BIOSYNTHETIC process from the neutrophil
      azurophil-granule paper. This mis-assigns the process direction - HEXA is a
      hydrolase that trims/degrades N-glycans (generating paucimannosidic structures),
      it does not synthesize glycosaminoglycans. The underlying activity is catabolic
      N-glycan trimming.
    action: MARK_AS_OVER_ANNOTATED
    reason: Wrong process direction (biosynthetic vs catabolic) for an experimental
      annotation; the actual activity is hydrolytic N-glycan trimming, captured by
      GO:0004563 and the catabolic GAG/glycan processes. Retained (not removed) per
      policy for experimental annotations, but flagged as over-/mis-annotated.
    supported_by:
    - reference_id: PMID:25645918
      supporting_text: by trimming hybrid/complex type N-glycan intermediates with relative broad
- term:
    id: GO:0008375
    label: acetylglucosaminyltransferase activity
  evidence_type: IDA
  original_reference_id: PMID:25645918
  qualifier: enables
  review:
    summary: IDA to acetylglucosaminyltransferase (glycosyltransferase) activity from the
      neutrophil azurophil-granule paper. This mis-classifies the enzyme - the paper
      shows Hex A generating paucimannosidic N-glycans by TRIMMING (hydrolysing) hybrid/
      complex N-glycan intermediates, i.e. a hydrolase acting in the catabolic direction,
      not a transferase adding GlcNAc.
    action: MARK_AS_OVER_ANNOTATED
    reason: Wrong enzyme class for the assigned MF; HEXA is a GH20 hydrolase, not a
      glycosyltransferase. The observed activity is hydrolytic N-glycan trimming
      (GO:0004563). Retained (not removed) per policy for experimental annotations, but
      flagged as mis-/over-annotated.
    supported_by:
    - reference_id: PMID:25645918
      supporting_text: displayed the capacity to generate paucimannosidic N-glycans
    - reference_id: PMID:25645918
      supporting_text: by trimming hybrid/complex type N-glycan intermediates with relative broad
- term:
    id: GO:0042582
    label: azurophil granule
  evidence_type: IDA
  original_reference_id: PMID:25645918
  qualifier: located_in
  review:
    summary: IDA localization to neutrophil azurophil granules, with immunocytochemical
      co-localization of beta-hexosaminidase A with the azurophilic marker MPO. A real
      but cell-type-specific, non-core location (azurophil granules are lysosome-related
      organelles).
    action: KEEP_AS_NON_CORE
    reason: Legitimate specialized localization in neutrophils; not the core (canonical
      lysosomal) site of action.
    supported_by:
    - reference_id: PMID:25645918
      supporting_text: and the azurophilic marker MPO in human
- term:
    id: GO:0070062
    label: extracellular exosome
  evidence_type: HDA
  original_reference_id: PMID:23533145
  qualifier: located_in
  review:
    summary: High-throughput proteomic detection of HEXA in urinary prostatic-secretion
      exosomes. A mass-spectrometry co-purification, indicative of secreted/exosomal
      presence rather than a core functional location.
    action: KEEP_AS_NON_CORE
    reason: Proteomic detection in exosomes; a non-core, incidental extracellular
      location for a lysosomal enzyme.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: oligosaccharide moieties from proteins and neutral glycolipids, or from
- term:
    id: GO:0016020
    label: membrane
  evidence_type: HDA
  original_reference_id: PMID:19946888
  qualifier: located_in
  review:
    summary: High-throughput detection in an NK-cell membrane-proteome study. HEXA is a
      soluble lumenal enzyme; its appearance in a membrane fraction reflects association
      with membranes/organelle co-purification, not integral membrane residence.
    action: MARK_AS_OVER_ANNOTATED
    reason: Non-specific 'membrane' from a high-throughput membrane-proteome dataset;
      HEXA is a soluble lysosomal enzyme, so integral-membrane localization is not
      supported.
    supported_by:
    - reference_id: file:human/HEXA/HEXA-uniprot.txt
      supporting_text: Lysosome
- term:
    id: GO:0046982
    label: protein heterodimerization activity
  evidence_type: IDA
  original_reference_id: PMID:6230359
  qualifier: enables
  review:
    summary: Direct biosynthetic study showing the alpha chain associates with the beta
      chain to form the mature alpha-beta heterodimer, an association required for
      catalytic activity and lysosomal transport. Informative molecular function
      underlying Hex A assembly.
    action: ACCEPT
    reason: Specific, informative heterodimerization activity (alpha-beta assembly),
      directly supported and biologically central.
    supported_by:
    - reference_id: PMID:6230359
      supporting_text: association with beta-chains is necessary not only for acquisition of catalytic
    - reference_id: PMID:6230359
      supporting_text: activity but also for transport of alpha-chains to lysosomes
core_functions:
- description: Lysosomal beta-N-acetylhexosaminidase (alpha subunit of hexosaminidase A,
    the alpha-beta heterodimer) that hydrolyses terminal non-reducing beta-linked
    N-acetyl-D-hexosamine residues from glycoconjugates; with the GM2-activator protein
    the alpha active site degrades GM2 ganglioside (GalNAc removal, GM2 -> GM3).
  molecular_function:
    id: GO:0004563
    label: beta-N-acetylhexosaminidase activity
  directly_involved_in:
  - id: GO:0006689
    label: ganglioside catabolic process
  - id: GO:0030203
    label: glycosaminoglycan metabolic process
  locations:
  - id: GO:0043202
    label: lysosomal lumen
  - id: GO:0005764
    label: lysosome
  in_complex:
    id: GO:1905379
    label: beta-N-acetylhexosaminidase complex
  supported_by:
  - reference_id: file:human/HEXA/HEXA-uniprot.txt
    supporting_text: Hydrolyzes the non-reducing end N-acetyl-D-hexosamine
  - reference_id: PMID:16698036
    supporting_text: Only the alpha-subunit active site can hydrolyze GM2 gangliosides
  - reference_id: PMID:8672428
    supporting_text: that can hydrolyze GM2 ganglioside in vivo, requiring the presence of the GM2
  - reference_id: PMID:6458607
    supporting_text: keratan sulfate-derived oligosaccharides with beta-N-acetylhexosaminidase
      A analogously resulted in the liberation of N-acetylglucosamine-6-sulfate
proposed_new_terms: []
suggested_questions:
- question: Beyond GM2 ganglioside, dermatan sulfate and keratan sulfate, which
    glycoconjugate substrates in vivo depend specifically on the HEXA alpha active site
    (as opposed to the beta active site of HEXB)?
- question: To what extent do secreted/exosomal and neutrophil azurophil-granule pools
    of hexosaminidase A have physiological (non-lysosomal) roles?
suggested_experiments:
- description: Substrate-resolved lysosomal glycomics in HEXA-null versus HEXB-null cells
    to define the alpha-subunit-specific substrate repertoire in vivo.
- description: Structure-guided mutagenesis of the alpha-specific loop and Arg424 to
    dissect GM2A-dependent GM2 recognition versus general hexosaminidase activity.
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO
    terms
  findings: []
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000044
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location
    vocabulary mapping, accompanied by conservative changes to GO terms applied by
    UniProt
  findings: []
- id: GO_REF:0000107
  title: Automatic transfer of experimentally verified manual GO annotation data to
    orthologs using Ensembl Compara
  findings: []
- id: GO_REF:0000117
  title: Electronic Gene Ontology annotations created by ARBA machine learning models
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: file:human/HEXA/HEXA-uniprot.txt
  title: HEXA UniProtKB record (P06865)
  findings: []
- id: PMID:11707436
  title: Physiological substrates for human lysosomal beta -hexosaminidase S.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Abstract-only cache; establishes alpha-subunit (Hex S/Hex A) activity
      on sulfated GAG fragments, dermatan sulfate and SM2, and GM2A stimulation.
- id: PMID:16698036
  title: 'Crystallographic structure of human beta-hexosaminidase A: interpretation
    of Tay-Sachs mutations and loss of GM2 ganglioside hydrolysis.'
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Hex A crystal structure; alpha-beta heterodimer, alpha-only GM2
      hydrolysis, and complex membership.
- id: PMID:19946888
  title: Defining the membrane proteome of NK cells.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: High-throughput NK-cell membrane proteome; incidental detection, not
      evidence of integral-membrane residence for this soluble lysosomal enzyme.
- id: PMID:23533145
  title: In-depth proteomic analyses of exosomes isolated from expressed prostatic
    secretions in urine.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: High-throughput exosome proteomics; supports a non-core exosomal pool.
- id: PMID:25645918
  title: Human neutrophils secrete bioactive paucimannosidic proteins from azurophilic
    granules into pathogen-infected sputum.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Supports azurophil-granule localization and N-glycan trimming
      (hydrolysis). The derived transferase (GO:0008375) and biosynthetic (GO:0006024)
      annotations mis-classify this hydrolytic/catabolic activity.
- id: PMID:27498570
  title: Endolysosomes Are the Principal Intracellular Sites of Acid Hydrolase Activity.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: General acid-hydrolase localization study (not HEXA-specific); basis
      for the IC endolysosome-lumen inference.
- id: PMID:28514442
  title: Architecture of the human interactome defines protein communities and disease
    networks.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: High-throughput interactome; source of a bare HEXA-HEXB protein-binding
      IPI.
- id: PMID:33961781
  title: Dual proteome-scale networks reveal cell-specific remodeling of the human
    interactome.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: High-throughput interactome; source of a bare HEXA-HEXB protein-binding
      IPI.
- id: PMID:33966596
  title: CREG1 promotes lysosomal biogenesis and function.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: CREG1 study using HEXA as a lysosomal/secreted marker; basis for the
      extracellular-region IDA.
- id: PMID:6230359
  title: Association of alpha- and beta-subunits during the biosynthesis of beta-hexosaminidase
    in cultured human fibroblasts.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Establishes alpha-beta heterodimerization required for catalytic
      maturation and lysosomal transport.
- id: PMID:6458607
  title: Liberation of N-acetylglucosamine-6-sulfate by human beta-N-acetylhexosaminidase
    A.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Hex A degrades keratan-sulfate-derived oligosaccharides, releasing
      sulfated N-acetylglucosamine; supports GAG catabolism and lysosomal lumen.
- id: PMID:8123671
  title: Classification of disorders of GM2 ganglioside hydrolysis using 3H-GM2 as
    substrate.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: 3H-GM2 hydrolysis assays distinguishing Tay-Sachs/Sandhoff; supports
      GM2 catabolism and hexosaminidase activity.
- id: PMID:8672428
  title: Direct determination of the substrate specificity of the alpha-active site
    in heterodimeric beta-hexosaminidase A.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Directly establishes the alpha-active-site specificity and the
      alpha-only GM2 hydrolysis (with GM2A) in Hex A.
- id: PMID:9694901
  title: A Pro504 --> Ser substitution in the beta-subunit of beta-hexosaminidase
    A inhibits alpha-subunit hydrolysis of GM2 ganglioside, resulting in chronic Sandhoff
    disease.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Confirms the alpha active site hydrolyses GM2 ganglioside and that
      beta-subunit elements modulate this natural-substrate activity.
- id: Reactome:R-HSA-1605595
  title: bHEXA hydrolyzes GM2A:GM2 to GM2A:GM3
  findings: []
- id: Reactome:R-HSA-1605632
  title: bHEXA,bHEXB hydrolyze PSAP(195-273):Gb4Cer:PE
  findings: []
- id: Reactome:R-HSA-1638053
  title: HEXA cleaves the terminal GlcNAc from keratan sulfate
  findings: []
- id: Reactome:R-HSA-2105001
  title: HEXA cleaves the terminal GalNAc from DS
  findings: []
- id: Reactome:R-HSA-2162225
  title: HEXA cleaves the terminal GlcNAc from small HA fragments
  findings: []
- id: Reactome:R-HSA-9035976
  title: Defective HEXA does not cleave the terminall GalNAc from small HA fragments
  findings: []
- id: Reactome:R-HSA-9840833
  title: bHEXA,bHEXB hydrolyze GM2A:GA2 to GM2A:LacCer
  findings: []
- id: Reactome:R-HSA-9840884
  title: bHEXA,bHEXS hydrolyze GM2A:SM2
  findings: []