Rule predicting proteoglycan catabolic process (GO:0030167) based on four condition sets: (1) beta-galactosidase in Eukaryota, (2) alpha-L-iduronidase, (3) beta-hexosaminidase in Mus, and (4) N-acetylglucosamine-6-sulfatase in Metazoa. These enzymes are lysosomal hydrolases involved in sequential degradation of glycosaminoglycan (GAG) chains that constitute proteoglycans. However, beta-galactosidase and beta-hexosaminidase are primarily known for ganglioside degradation, raising questions about annotation specificity.
Interactive prediction matrix showing how row entries PREDICT column entries. Cell (i,j) shows what fraction of proteins with row domain i also have column domain j. Click cells to view intersection in UniProt. Click domain IDs to view proteins with that domain.
Legend: Each cell shows PREDICTS % (fraction of row entry proteins that also have column entry - row PREDICTS column), Jaccard similarity (J:%), and intersection count. CS = Condition Set(s), TGT = GO annotation target.
This rule captures four lysosomal glycosidases and sulfatases that participate in proteoglycan catabolism through degradation of glycosaminoglycan chains. Condition set 2 (alpha-L-iduronidase) and condition set 4 (N-acetylglucosamine-6-sulfatase) are strongly appropriate—these enzymes are exclusively or primarily involved in degrading dermatan sulfate, heparan sulfate, and related GAG chains, with well-characterized mucopolysaccharidosis phenotypes when deficient. Condition sets 1 (beta-galactosidase) and 3 (beta-hexosaminidase) are technically correct but biologically problematic—while these enzymes do participate in keratan sulfate degradation, their primary biological roles and clinical significance relate to ganglioside catabolism (GM1 and GM2 respectively). The taxonomic scope is inconsistent and raises questions: condition set 1 uses broad Eukaryota scope, condition set 3 uses narrow Mus restriction (creating false negatives), and condition set 4 uses appropriate Metazoa scope. The rule demonstrates a tension between biochemical accuracy (all four enzymes can cleave bonds in GAG chains) and biological interpretation (two are primarily ganglioside-degrading enzymes with secondary GAG functions). More specific annotations or hierarchical annotation strategies would improve utility.
The rule requires modification to improve biological accuracy and reduce potential misinterpretation. Three specific issues need addressing: (1) Condition sets 1 (beta-galactosidase) and 3 (beta-hexosaminidase) should either be removed from this rule or receive additional primary annotations reflecting their ganglioside-degrading functions (e.g., "GM1 ganglioside catabolic process" GO:0006689 for GLB1, "ganglioside catabolic process" GO:0006687 or "GM2 ganglioside catabolic process" for hexosaminidase). A hierarchical annotation strategy where proteins receive both primary (ganglioside) and secondary (proteoglycan) annotations would be most accurate. (2) The Mus restriction in condition set 3 is unjustified and creates false negatives—beta-hexosaminidase function in keratan sulfate degradation is conserved across mammals minimally, likely across vertebrates. This scope should be expanded to at least Mammalia or Vertebrata. (3) Consider splitting this rule: create a focused rule for core proteoglycan-degrading enzymes (IDUA, GNS, and other MPS-associated enzymes) separate from dual-function enzymes that also degrade gangliosides. This would improve both precision and biological interpretability while maintaining computational utility.
Beta-galactosidase (GLB1 in humans) is a lysosomal hydrolase that cleaves terminal beta-linked galactose residues from glycoconjugates. While it does participate in keratan sulfate degradation (a glycosaminoglycan component of proteoglycans), its primary clinical significance relates to GM1 ganglioside catabolism. GLB1 deficiency causes two distinct diseases: GM1 gangliosidosis (impaired ganglioside degradation) and mucopolysaccharidosis type IVB/Morquio B (impaired keratan sulfate degradation). The dual substrate specificity reflects the enzyme's ability to cleave β-galactose from structurally diverse molecules. While annotating GLB1 with proteoglycan catabolic process is technically correct for the keratan sulfate degradation function, this annotation obscures the enzyme's primary role in ganglioside metabolism.
| Condition A | Condition B | Count A | Count B | Intersection | Jaccard | A in B | B in A | Interpretation |
|---|---|---|---|---|---|---|---|---|
2.60.120.260:FF:000115
|
3.20.20.80:FF:000017
|
7 | 10 | 7 | 0.700 | 1.000 | 0.700 | SUBSET |
Alpha-L-iduronidase (IDUA) is a lysosomal enzyme that cleaves terminal alpha-L-iduronic acid residues from dermatan sulfate and heparan sulfate, both of which are glycosaminoglycan chains attached to proteoglycan core proteins. IDUA deficiency causes mucopolysaccharidosis type I (MPS I), including Hurler syndrome and Scheie syndrome, characterized by accumulation of dermatan sulfate and heparan sulfate in multiple tissues. This is a quintessential proteoglycan catabolic enzyme with no known alternative primary function. The condition set appropriately targets this enzyme family and the GO:0030167 annotation is highly appropriate. Over 201 IDUA mutations have been identified, and enzyme replacement therapy (Aldurazyme) is available for treatment.
| Condition A | Condition B | Count A | Count B | Intersection | Jaccard | A in B | B in A | Interpretation |
|---|---|---|---|---|---|---|---|---|
2.60.40.10:FF:001526
|
2.60.40.1500:FF:000001
|
3 | 3 | 3 | 1.000 | 1.000 | 1.000 | REDUNDANT |
2.60.40.10:FF:001526
|
3.20.20.80:FF:000059
|
3 | 3 | 3 | 1.000 | 1.000 | 1.000 | REDUNDANT |
2.60.40.1500:FF:000001
|
3.20.20.80:FF:000059
|
3 | 3 | 3 | 1.000 | 1.000 | 1.000 | REDUNDANT |
Beta-hexosaminidase exists as two isoenzymes in mammals: Hex A (heterodimer of alpha/HEXA and beta/HEXB subunits) and Hex B (homodimer of beta subunits). While beta-hexosaminidase does participate in keratan sulfate degradation by removing terminal N-acetyl-D-galactosamine residues, its primary clinical and biological significance relates to GM2 ganglioside catabolism. HEXA deficiency causes Tay-Sachs disease and HEXB deficiency causes Sandhoff disease, both characterized primarily by GM2 ganglioside accumulation leading to neurodegeneration. The restriction to Mus genus (862507) is puzzling and appears arbitrary—beta-hexosaminidase function in proteoglycan catabolism is conserved across mammals and other vertebrates. This narrow taxonomic scope creates false negatives for the same enzyme function in closely related organisms. Similar to beta-galactosidase, GO:0030167 annotation is technically correct but potentially misleading about the enzyme's primary biological role.
| Condition A | Condition B | Count A | Count B | Intersection | Jaccard | A in B | B in A | Interpretation |
|---|---|---|---|---|---|---|---|---|
3.20.20.80:FF:000049
|
3.30.379.10:FF:000001
|
9 | 7 | 7 | 0.778 | 0.778 | 1.000 | SUBSET |
N-acetylglucosamine-6-sulfatase (GNS) is a lysosomal enzyme that specifically removes 6-sulfate groups from N-acetylglucosamine residues in heparan sulfate, a glycosaminoglycan component of proteoglycans. GNS deficiency causes Sanfilippo syndrome type D (mucopolysaccharidosis type IIID), a neurodegenerative lysosomal storage disorder characterized by heparan sulfate accumulation. Unlike beta-galactosidase and beta-hexosaminidase, GNS is exclusively involved in glycosaminoglycan catabolism with no known role in ganglioside metabolism. The Metazoa restriction is appropriate and well-supported, as the enzyme functions in heparan sulfate degradation across animals. This is a strong, specific match for proteoglycan catabolic process. GNS represents one of five enzymes (types A-E) involved exclusively in heparan sulfate degradation, and deficiency of any causes distinct Sanfilippo syndrome subtypes.
The rule uses four condition sets but lacks parsimony in two respects. First, it conflates enzymes with distinct primary biological functions—dedicated GAG-degrading enzymes (IDUA, GNS) versus dual-function enzymes with primary ganglioside-degrading roles (GLB1, Hex A/B). This creates a heterogeneous rule that obscures important functional distinctions. Second, condition set 3 combines two beta-hexosaminidase FunFams with an arbitrary Mus-only restriction, while condition set 1 uses broad Eukaryota scope for structurally similar beta-galactosidase—this inconsistency suggests the taxonomic constraints were not systematically designed. A more parsimonious approach would split the rule into: (a) a focused rule for enzymes primarily involved in proteoglycan catabolism (IDUA, GNS, potentially expanded to other MPS enzymes), and (b) a separate rule or hierarchical annotation strategy for dual-function enzymes. Within each condition set, the use of multiple FunFam signatures for the same enzyme is appropriate for capturing sequence diversity, but the overall rule structure lacks biological parsimony.
All four condition sets have extensive experimental support. Alpha-L-iduronidase (condition set 2): Over 201 IDUA mutations documented, enzyme replacement therapy (Aldurazyme) approved, crystal structures solved, dermatan sulfate and heparan sulfate accumulation demonstrated in MPS I patients. N-acetylglucosamine-6-sulfatase (condition set 4): GNS mutations cause Sanfilippo D with specific heparan sulfate accumulation, enzyme assays demonstrate substrate specificity, recombinant enzyme therapy under development. Beta-galactosidase (condition set 1): GLB1 mutations cause distinct phenotypes (GM1 gangliosidosis versus MPS IVB) depending on residual activity toward different substrates, crystal structures explain substrate binding, enzyme assays confirm dual specificity for GM1 ganglioside and keratan sulfate. Beta-hexosaminidase (condition set 3): HEXA and HEXB mutations cause Tay-Sachs and Sandhoff diseases respectively, crystal structures of Hex A and Hex B solved, substrate specificity for GM2 ganglioside and keratan sulfate experimentally validated. The literature strongly supports that all four enzymes can hydrolyze bonds in GAG chains, but also clearly demonstrates that beta-galactosidase and beta-hexosaminidase have primary roles in ganglioside rather than proteoglycan metabolism.
The four condition sets target distinct enzyme families with no sequence or structural overlap. Condition set 1 targets beta-galactosidase (GLB1, GH35 family), condition set 2 targets alpha-L-iduronidase (IDUA, GH39 family), condition set 3 targets beta-hexosaminidase (HEXA/HEXB, GH20 family), and condition set 4 targets N-acetylglucosamine-6-sulfatase (GNS, sulfatase family). These represent independent evolutionary solutions to specific bond cleavage reactions in GAG degradation. Mechanistically, they cleave different bonds: beta-galactosidase removes terminal beta-galactose, alpha-L-iduronidase removes alpha-L-iduronate, beta-hexosaminidase removes N-acetylhexosamine, and GNS removes 6-sulfate from N-acetylglucosamine. The enzymes act sequentially in lysosomal GAG catabolism pathways but do not overlap in substrate specificity. However, there is functional overlap in the sense that beta-galactosidase and beta-hexosaminidase both have primary roles in ganglioside catabolism, creating a different kind of "overlap" issue—overlap in biological context rather than molecular specificity.
GO:0030167 (proteoglycan catabolic process) shows variable appropriateness across the four condition sets. For condition set 2 (alpha-L-iduronidase) and condition set 4 (N-acetylglucosamine-6-sulfatase), GO:0030167 is highly appropriate and could potentially be made more specific with child terms like "dermatan sulfate catabolic process" (GO:1902556) or "heparan sulfate proteoglycan catabolic process" (GO:0030200). For condition sets 1 (beta-galactosidase) and 3 (beta-hexosaminidase), GO:0030167 is technically accurate but too broad and potentially misleading—it fails to capture the primary biological roles of these enzymes in ganglioside metabolism. More appropriate primary annotations would be "GM1 ganglioside catabolic process" (GO:0006689) for GLB1 and "ganglioside catabolic process" (GO:0006687) or "GM2 ganglioside catabolic process" for hexosaminidase. The current annotation strategy creates a situation where users searching for proteoglycan-degrading enzymes will retrieve GLB1 and hexosaminidase, potentially not understanding that these enzymes' primary functions lie elsewhere. A hierarchical annotation approach with both primary and secondary GO terms would better reflect the biological reality.
The taxonomic scopes across condition sets are inconsistent and in one case appear arbitrary. Condition set 1 uses Eukaryota (NCBITaxon:2759), an extremely broad scope appropriate for the widespread distribution of beta-galactosidase across eukaryotes. Condition set 2 has no taxonomic restriction, which is appropriate given IDUA's conservation across animals and potentially other eukaryotes. Condition set 3 uses Mus (NCBITaxon:862507), restricting to mouse and rat genera—this is unjustifiably narrow and creates false negatives for the same enzyme function in other mammals, vertebrates, and potentially all animals. Beta-hexosaminidase function in keratan sulfate degradation is conserved across mammals at minimum, and the Mus restriction appears arbitrary or erroneous. Condition set 4 uses Metazoa (NCBITaxon:33208), which is appropriate for N-acetylglucosamine-6-sulfatase function in animals. The inconsistency suggests the rule was not designed with systematic consideration of taxonomic distribution. Condition set 3 should be expanded to at least Mammalia (40674) or Vertebrata (7742), and ideally the entire rule should use consistent taxonomic scope logic.
Beta-galactosidase (GLB1) removes terminal β-galactose from keratan sulfate and oligosaccharides in lysosome, contributing to proteoglycan fragment trimming, but is multifunctional and primarily associated with GM1 gangliosidosis.
Alpha-L-iduronidase (IDUA) is strongly diagnostic for HS/DS catabolism, hydrolyzes terminal α-L-iduronic acid, with no prominent alternative functions. Deficiency causes MPS I.
Beta-hexosaminidase A/B (HEXA/HEXB) primarily involved in ganglioside catabolism; has broad specificity for terminal HexNAc but direct role in proteoglycan degradation is indirect. Annotation risks overannotation without additional constraints.
N-acetylglucosamine-6-sulfatase (GNS) is obligatory for HS proteoglycan catabolism, removes 6-O-sulfate from terminal GlcNAc. Strongly tied to HS degradation with no alternative functions. Deficiency causes MPS IIID.
GO:0030167 appropriate for IDUA and GNS but may be too broad for HEXA/HEXB without additional evidence. More specific terms recommended when possible (heparan sulfate catabolic process, dermatan sulfate catabolic process, keratan sulfate catabolic process).
Hurler syndrome is an autosomal recessive disorder caused by defective IDUA gene encoding alpha-L-iduronidase on chromosome 4, resulting in accumulation of dermatan sulfate and heparan sulfate in multiple tissues.
Sanfilippo syndrome type D is caused by N-acetylglucosamine-6-sulfate sulfatase deficiency required for heparan sulfate degradation, with excessive heparan sulfate accumulation in patient fibroblasts.
Beta-galactosidase encoded by GLB1 is involved in metabolism of GM1 ganglioside and keratan sulfate. Deficiency causes GM1 gangliosidosis or mucopolysaccharidosis type IVB depending on substrate specificity of variants.
GLB1-related disorders comprise two phenotypically distinct diseases: GM1 gangliosidosis (impaired ganglioside degradation) and MPS IVB (impaired keratan sulfate degradation), reflecting dual substrate specificity.
Beta-hexosaminidase A breaks down GM2 ganglioside in lysosomes. HEXA variants causing Tay-Sachs disease eliminate enzyme activity, causing GM2 accumulation and progressive neuronal damage.
Crystal structure explains substrate specificity of beta-hexosaminidase B (HEXB homodimer) for GM2 ganglioside, oligosaccharides, and keratan sulfate. Mutations cause Sandhoff disease.
GAG degradation occurs via sulfatase-catalyzed sulfate removal and sequential exoglycosidase action. At least 14 lysosomal storage diseases affect GAG catabolism, including mucopolysaccharidoses.
Glycosaminoglycans include heparan sulfate, dermatan sulfate, chondroitin sulfate, and keratan sulfate. Sequential degradation requires specific lysosomal enzymes; deficiencies cause mucopolysaccharidoses.
id: ARBA00085883
description: 'Rule predicting proteoglycan catabolic process (GO:0030167) based on
four condition sets: (1) beta-galactosidase in Eukaryota, (2) alpha-L-iduronidase,
(3) beta-hexosaminidase in Mus, and (4) N-acetylglucosamine-6-sulfatase in Metazoa.
These enzymes are lysosomal hydrolases involved in sequential degradation of glycosaminoglycan
(GAG) chains that constitute proteoglycans. However, beta-galactosidase and beta-hexosaminidase
are primarily known for ganglioside degradation, raising questions about annotation
specificity.'
status: COMPLETE
rule_type: ARBA
rule:
rule_id: ARBA00085883
condition_sets:
- number: 1
conditions:
- condition_type: FUNFAM
value: 2.60.120.260:FF:000115
curie: CATH.FunFam:2.60.120.260:FF:000115
label: Beta-galactosidase
negated: false
- condition_type: FUNFAM
value: 3.20.20.80:FF:000017
curie: CATH.FunFam:3.20.20.80:FF:000017
label: Beta-galactosidase
negated: false
- condition_type: TAXON
value: '2759'
curie: NCBITaxon:2759
label: Eukaryota
negated: false
notes: 'Beta-galactosidase (GLB1 in humans) is a lysosomal hydrolase that cleaves
terminal beta-linked galactose residues from glycoconjugates. While it does
participate in keratan sulfate degradation (a glycosaminoglycan component of
proteoglycans), its primary clinical significance relates to GM1 ganglioside
catabolism. GLB1 deficiency causes two distinct diseases: GM1 gangliosidosis
(impaired ganglioside degradation) and mucopolysaccharidosis type IVB/Morquio
B (impaired keratan sulfate degradation). The dual substrate specificity reflects
the enzyme''s ability to cleave β-galactose from structurally diverse molecules.
While annotating GLB1 with proteoglycan catabolic process is technically correct
for the keratan sulfate degradation function, this annotation obscures the enzyme''s
primary role in ganglioside metabolism.'
pairwise_overlap:
- condition_a: 2.60.120.260:FF:000115
condition_b: 3.20.20.80:FF:000017
protein_database: SWISSPROT
count_a: 7
count_b: 10
intersection_count: 7
a_minus_b_count: 0
b_minus_a_count: 3
jaccard_similarity: 0.7
containment_a_in_b: 1.0
containment_b_in_a: 0.7
interpretation: SUBSET
- number: 2
conditions:
- condition_type: FUNFAM
value: 2.60.40.10:FF:001526
curie: CATH.FunFam:2.60.40.10:FF:001526
label: Alpha-L-iduronidase
negated: false
- condition_type: FUNFAM
value: 2.60.40.1500:FF:000001
curie: CATH.FunFam:2.60.40.1500:FF:000001
label: Alpha-L-iduronidase
negated: false
- condition_type: FUNFAM
value: 3.20.20.80:FF:000059
curie: CATH.FunFam:3.20.20.80:FF:000059
label: Alpha-L-iduronidase
negated: false
notes: Alpha-L-iduronidase (IDUA) is a lysosomal enzyme that cleaves terminal
alpha-L-iduronic acid residues from dermatan sulfate and heparan sulfate, both
of which are glycosaminoglycan chains attached to proteoglycan core proteins.
IDUA deficiency causes mucopolysaccharidosis type I (MPS I), including Hurler
syndrome and Scheie syndrome, characterized by accumulation of dermatan sulfate
and heparan sulfate in multiple tissues. This is a quintessential proteoglycan
catabolic enzyme with no known alternative primary function. The condition set
appropriately targets this enzyme family and the GO:0030167 annotation is highly
appropriate. Over 201 IDUA mutations have been identified, and enzyme replacement
therapy (Aldurazyme) is available for treatment.
pairwise_overlap:
- condition_a: 2.60.40.10:FF:001526
condition_b: 2.60.40.1500:FF:000001
protein_database: SWISSPROT
count_a: 3
count_b: 3
intersection_count: 3
a_minus_b_count: 0
b_minus_a_count: 0
jaccard_similarity: 1.0
containment_a_in_b: 1.0
containment_b_in_a: 1.0
interpretation: REDUNDANT
- condition_a: 2.60.40.10:FF:001526
condition_b: 3.20.20.80:FF:000059
protein_database: SWISSPROT
count_a: 3
count_b: 3
intersection_count: 3
a_minus_b_count: 0
b_minus_a_count: 0
jaccard_similarity: 1.0
containment_a_in_b: 1.0
containment_b_in_a: 1.0
interpretation: REDUNDANT
- condition_a: 2.60.40.1500:FF:000001
condition_b: 3.20.20.80:FF:000059
protein_database: SWISSPROT
count_a: 3
count_b: 3
intersection_count: 3
a_minus_b_count: 0
b_minus_a_count: 0
jaccard_similarity: 1.0
containment_a_in_b: 1.0
containment_b_in_a: 1.0
interpretation: REDUNDANT
- number: 3
conditions:
- condition_type: FUNFAM
value: 3.20.20.80:FF:000049
curie: CATH.FunFam:3.20.20.80:FF:000049
label: Beta-hexosaminidase A
negated: false
- condition_type: FUNFAM
value: 3.30.379.10:FF:000001
curie: CATH.FunFam:3.30.379.10:FF:000001
label: Beta-hexosaminidase subunit beta
negated: false
- condition_type: TAXON
value: '862507'
curie: NCBITaxon:862507
label: Mus
negated: false
notes: 'Beta-hexosaminidase exists as two isoenzymes in mammals: Hex A (heterodimer
of alpha/HEXA and beta/HEXB subunits) and Hex B (homodimer of beta subunits).
While beta-hexosaminidase does participate in keratan sulfate degradation by
removing terminal N-acetyl-D-galactosamine residues, its primary clinical and
biological significance relates to GM2 ganglioside catabolism. HEXA deficiency
causes Tay-Sachs disease and HEXB deficiency causes Sandhoff disease, both characterized
primarily by GM2 ganglioside accumulation leading to neurodegeneration. The
restriction to Mus genus (862507) is puzzling and appears arbitrary—beta-hexosaminidase
function in proteoglycan catabolism is conserved across mammals and other vertebrates.
This narrow taxonomic scope creates false negatives for the same enzyme function
in closely related organisms. Similar to beta-galactosidase, GO:0030167 annotation
is technically correct but potentially misleading about the enzyme''s primary
biological role.'
pairwise_overlap:
- condition_a: 3.20.20.80:FF:000049
condition_b: 3.30.379.10:FF:000001
protein_database: SWISSPROT
count_a: 9
count_b: 7
intersection_count: 7
a_minus_b_count: 2
b_minus_a_count: 0
jaccard_similarity: 0.7777777777777778
containment_a_in_b: 0.7777777777777778
containment_b_in_a: 1.0
interpretation: SUBSET
- number: 4
conditions:
- condition_type: FUNFAM
value: 3.40.720.10:FF:000012
curie: CATH.FunFam:3.40.720.10:FF:000012
label: N-acetylglucosamine-6-sulfatase
negated: false
- condition_type: TAXON
value: '33208'
curie: NCBITaxon:33208
label: Metazoa
negated: false
notes: N-acetylglucosamine-6-sulfatase (GNS) is a lysosomal enzyme that specifically
removes 6-sulfate groups from N-acetylglucosamine residues in heparan sulfate,
a glycosaminoglycan component of proteoglycans. GNS deficiency causes Sanfilippo
syndrome type D (mucopolysaccharidosis type IIID), a neurodegenerative lysosomal
storage disorder characterized by heparan sulfate accumulation. Unlike beta-galactosidase
and beta-hexosaminidase, GNS is exclusively involved in glycosaminoglycan catabolism
with no known role in ganglioside metabolism. The Metazoa restriction is appropriate
and well-supported, as the enzyme functions in heparan sulfate degradation across
animals. This is a strong, specific match for proteoglycan catabolic process.
GNS represents one of five enzymes (types A-E) involved exclusively in heparan
sulfate degradation, and deficiency of any causes distinct Sanfilippo syndrome
subtypes.
go_annotations:
- go_id: GO:0030167
go_label: proteoglycan catabolic process
aspect: BP
reviewed_protein_count: 0
unreviewed_protein_count: 0
created_date: '2025-03-21'
modified_date: '2025-03-21'
entries:
- id: 2.60.120.260:FF:000115
type: FUNFAM
label: Beta-galactosidase
appears_in_condition_sets:
- 1
protein_count: 7
related_entries:
- relationship: PREDICTS
target_id: 3.20.20.80:FF:000017
containment: 1.0
jaccard_similarity: 0.7
intersection_count: 7
exclusive_count: 0
- relationship: EQUIV
target_id: 2.60.40.10:FF:001526
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 7
- relationship: EQUIV
target_id: 2.60.40.1500:FF:000001
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 7
- relationship: EQUIV
target_id: 3.20.20.80:FF:000059
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 7
- relationship: EQUIV
target_id: 3.20.20.80:FF:000049
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 7
- relationship: EQUIV
target_id: 3.30.379.10:FF:000001
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 7
- relationship: EQUIV
target_id: 3.40.720.10:FF:000012
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 7
- relationship: PREDICTS
target_id: GO:0030167
containment: 0.429
jaccard_similarity: 0.051
intersection_count: 3
exclusive_count: 4
- id: 2.60.40.10:FF:001526
type: FUNFAM
label: Alpha-L-iduronidase
appears_in_condition_sets:
- 2
protein_count: 3
related_entries:
- relationship: EQUIV
target_id: 2.60.120.260:FF:000115
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 3
- relationship: EQUIV
target_id: 3.20.20.80:FF:000017
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 3
- relationship: EQUIV
target_id: 2.60.40.1500:FF:000001
containment: 1.0
jaccard_similarity: 1.0
intersection_count: 3
exclusive_count: 0
- relationship: EQUIV
target_id: 3.20.20.80:FF:000059
containment: 1.0
jaccard_similarity: 1.0
intersection_count: 3
exclusive_count: 0
- relationship: EQUIV
target_id: 3.20.20.80:FF:000049
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 3
- relationship: EQUIV
target_id: 3.30.379.10:FF:000001
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 3
- relationship: EQUIV
target_id: 3.40.720.10:FF:000012
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 3
- relationship: PREDICTS
target_id: GO:0030167
containment: 1.0
jaccard_similarity: 0.055
intersection_count: 3
exclusive_count: 0
- id: 2.60.40.1500:FF:000001
type: FUNFAM
label: Alpha-L-iduronidase
appears_in_condition_sets:
- 2
protein_count: 3
related_entries:
- relationship: EQUIV
target_id: 2.60.120.260:FF:000115
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 3
- relationship: EQUIV
target_id: 3.20.20.80:FF:000017
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 3
- relationship: EQUIV
target_id: 2.60.40.10:FF:001526
containment: 1.0
jaccard_similarity: 1.0
intersection_count: 3
exclusive_count: 0
- relationship: EQUIV
target_id: 3.20.20.80:FF:000059
containment: 1.0
jaccard_similarity: 1.0
intersection_count: 3
exclusive_count: 0
- relationship: EQUIV
target_id: 3.20.20.80:FF:000049
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 3
- relationship: EQUIV
target_id: 3.30.379.10:FF:000001
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 3
- relationship: EQUIV
target_id: 3.40.720.10:FF:000012
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 3
- relationship: PREDICTS
target_id: GO:0030167
containment: 1.0
jaccard_similarity: 0.055
intersection_count: 3
exclusive_count: 0
- id: 3.20.20.80:FF:000017
type: FUNFAM
label: Beta-galactosidase
appears_in_condition_sets:
- 1
protein_count: 10
related_entries:
- relationship: PREDICTED_BY
target_id: 2.60.120.260:FF:000115
containment: 0.7
jaccard_similarity: 0.7
intersection_count: 7
exclusive_count: 3
- relationship: EQUIV
target_id: 2.60.40.10:FF:001526
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 10
- relationship: EQUIV
target_id: 2.60.40.1500:FF:000001
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 10
- relationship: EQUIV
target_id: 3.20.20.80:FF:000059
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 10
- relationship: EQUIV
target_id: 3.20.20.80:FF:000049
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 10
- relationship: EQUIV
target_id: 3.30.379.10:FF:000001
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 10
- relationship: EQUIV
target_id: 3.40.720.10:FF:000012
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 10
- relationship: PREDICTS
target_id: GO:0030167
containment: 0.3
jaccard_similarity: 0.048
intersection_count: 3
exclusive_count: 7
- id: 3.20.20.80:FF:000049
type: FUNFAM
label: Beta-hexosaminidase A
appears_in_condition_sets:
- 3
protein_count: 9
related_entries:
- relationship: EQUIV
target_id: 2.60.120.260:FF:000115
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 9
- relationship: EQUIV
target_id: 3.20.20.80:FF:000017
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 9
- relationship: EQUIV
target_id: 2.60.40.10:FF:001526
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 9
- relationship: EQUIV
target_id: 2.60.40.1500:FF:000001
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 9
- relationship: EQUIV
target_id: 3.20.20.80:FF:000059
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 9
- relationship: PREDICTED_BY
target_id: 3.30.379.10:FF:000001
containment: 1.0
jaccard_similarity: 0.778
intersection_count: 7
exclusive_count: 0
- relationship: EQUIV
target_id: 3.40.720.10:FF:000012
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 9
- relationship: PREDICTS
target_id: GO:0030167
containment: 0.778
jaccard_similarity: 0.123
intersection_count: 7
exclusive_count: 2
- id: 3.20.20.80:FF:000059
type: FUNFAM
label: Alpha-L-iduronidase
appears_in_condition_sets:
- 2
protein_count: 3
related_entries:
- relationship: EQUIV
target_id: 2.60.120.260:FF:000115
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 3
- relationship: EQUIV
target_id: 3.20.20.80:FF:000017
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 3
- relationship: EQUIV
target_id: 2.60.40.10:FF:001526
containment: 1.0
jaccard_similarity: 1.0
intersection_count: 3
exclusive_count: 0
- relationship: EQUIV
target_id: 2.60.40.1500:FF:000001
containment: 1.0
jaccard_similarity: 1.0
intersection_count: 3
exclusive_count: 0
- relationship: EQUIV
target_id: 3.20.20.80:FF:000049
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 3
- relationship: EQUIV
target_id: 3.30.379.10:FF:000001
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 3
- relationship: EQUIV
target_id: 3.40.720.10:FF:000012
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 3
- relationship: PREDICTS
target_id: GO:0030167
containment: 1.0
jaccard_similarity: 0.055
intersection_count: 3
exclusive_count: 0
- id: 3.30.379.10:FF:000001
type: FUNFAM
label: Beta-hexosaminidase subunit beta
appears_in_condition_sets:
- 3
protein_count: 7
related_entries:
- relationship: EQUIV
target_id: 2.60.120.260:FF:000115
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 7
- relationship: EQUIV
target_id: 3.20.20.80:FF:000017
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 7
- relationship: EQUIV
target_id: 2.60.40.10:FF:001526
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 7
- relationship: EQUIV
target_id: 2.60.40.1500:FF:000001
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 7
- relationship: EQUIV
target_id: 3.20.20.80:FF:000059
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 7
- relationship: PREDICTS
target_id: 3.20.20.80:FF:000049
containment: 0.778
jaccard_similarity: 0.778
intersection_count: 7
exclusive_count: 2
- relationship: EQUIV
target_id: 3.40.720.10:FF:000012
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 7
- relationship: PREDICTS
target_id: GO:0030167
containment: 0.857
jaccard_similarity: 0.107
intersection_count: 6
exclusive_count: 1
- id: 3.40.720.10:FF:000012
type: FUNFAM
label: N-acetylglucosamine-6-sulfatase
appears_in_condition_sets:
- 4
protein_count: 4
related_entries:
- relationship: EQUIV
target_id: 2.60.120.260:FF:000115
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 4
- relationship: EQUIV
target_id: 3.20.20.80:FF:000017
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 4
- relationship: EQUIV
target_id: 2.60.40.10:FF:001526
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 4
- relationship: EQUIV
target_id: 2.60.40.1500:FF:000001
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 4
- relationship: EQUIV
target_id: 3.20.20.80:FF:000059
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 4
- relationship: EQUIV
target_id: 3.20.20.80:FF:000049
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 4
- relationship: EQUIV
target_id: 3.30.379.10:FF:000001
containment: 0.0
jaccard_similarity: 0.0
intersection_count: 0
exclusive_count: 4
- relationship: PREDICTS
target_id: GO:0030167
containment: 0.5
jaccard_similarity: 0.035
intersection_count: 2
exclusive_count: 2
review_summary: 'This rule captures four lysosomal glycosidases and sulfatases that
participate in proteoglycan catabolism through degradation of glycosaminoglycan
chains. Condition set 2 (alpha-L-iduronidase) and condition set 4 (N-acetylglucosamine-6-sulfatase)
are strongly appropriate—these enzymes are exclusively or primarily involved in
degrading dermatan sulfate, heparan sulfate, and related GAG chains, with well-characterized
mucopolysaccharidosis phenotypes when deficient. Condition sets 1 (beta-galactosidase)
and 3 (beta-hexosaminidase) are technically correct but biologically problematic—while
these enzymes do participate in keratan sulfate degradation, their primary biological
roles and clinical significance relate to ganglioside catabolism (GM1 and GM2 respectively).
The taxonomic scope is inconsistent and raises questions: condition set 1 uses broad
Eukaryota scope, condition set 3 uses narrow Mus restriction (creating false negatives),
and condition set 4 uses appropriate Metazoa scope. The rule demonstrates a tension
between biochemical accuracy (all four enzymes can cleave bonds in GAG chains) and
biological interpretation (two are primarily ganglioside-degrading enzymes with
secondary GAG functions). More specific annotations or hierarchical annotation strategies
would improve utility.'
action: MODIFY
action_rationale: 'The rule requires modification to improve biological accuracy and
reduce potential misinterpretation. Three specific issues need addressing: (1) Condition
sets 1 (beta-galactosidase) and 3 (beta-hexosaminidase) should either be removed
from this rule or receive additional primary annotations reflecting their ganglioside-degrading
functions (e.g., "GM1 ganglioside catabolic process" GO:0006689 for GLB1, "ganglioside
catabolic process" GO:0006687 or "GM2 ganglioside catabolic process" for hexosaminidase).
A hierarchical annotation strategy where proteins receive both primary (ganglioside)
and secondary (proteoglycan) annotations would be most accurate. (2) The Mus restriction
in condition set 3 is unjustified and creates false negatives—beta-hexosaminidase
function in keratan sulfate degradation is conserved across mammals minimally, likely
across vertebrates. This scope should be expanded to at least Mammalia or Vertebrata.
(3) Consider splitting this rule: create a focused rule for core proteoglycan-degrading
enzymes (IDUA, GNS, and other MPS-associated enzymes) separate from dual-function
enzymes that also degrade gangliosides. This would improve both precision and biological
interpretability while maintaining computational utility.'
suggested_modifications:
- Remove condition sets 1 and 3 from this rule and create separate rules for ganglioside-degrading
enzymes with dual substrate specificity
- Alternatively, add hierarchical GO annotations where GLB1 receives both "GM1 ganglioside
catabolic process" (primary) and "proteoglycan catabolic process" (secondary)
- Add hierarchical GO annotations where beta-hexosaminidase receives both "GM2 ganglioside
catabolic process" or "ganglioside catabolic process" (primary) and "proteoglycan
catabolic process" (secondary)
- Expand condition set 3 taxonomic scope from Mus (862507) to at minimum Mammalia
(40674) or preferably Vertebrata (7742)
- Consider adding other core proteoglycan-degrading enzymes to strengthen the rule
(iduronate-2-sulfatase/IDS for MPS II, N-acetylgalactosamine-6-sulfatase/GALNS for
MPS IVA, and other MPS-associated enzymes)
- Add more specific child term annotations where appropriate (heparan sulfate catabolic
process for GNS, dermatan sulfate catabolic process for IDUA)
- Document the distinction between primary proteoglycan-degrading enzymes and dual-function
enzymes in rule metadata
parsimony:
assessment: REDUNDANT
notes: 'The rule uses four condition sets but lacks parsimony in two respects. First,
it conflates enzymes with distinct primary biological functions—dedicated GAG-degrading
enzymes (IDUA, GNS) versus dual-function enzymes with primary ganglioside-degrading
roles (GLB1, Hex A/B). This creates a heterogeneous rule that obscures important
functional distinctions. Second, condition set 3 combines two beta-hexosaminidase
FunFams with an arbitrary Mus-only restriction, while condition set 1 uses broad
Eukaryota scope for structurally similar beta-galactosidase—this inconsistency
suggests the taxonomic constraints were not systematically designed. A more parsimonious
approach would split the rule into: (a) a focused rule for enzymes primarily involved
in proteoglycan catabolism (IDUA, GNS, potentially expanded to other MPS enzymes),
and (b) a separate rule or hierarchical annotation strategy for dual-function
enzymes. Within each condition set, the use of multiple FunFam signatures for
the same enzyme is appropriate for capturing sequence diversity, but the overall
rule structure lacks biological parsimony.'
supported_by:
- reference_id: web:https://www.ncbi.nlm.nih.gov/books/NBK164500/
supporting_text: 'GLB1-related disorders comprise two phenotypically distinct
lysosomal storage disorders: GM1 gangliosidosis and mucopolysaccharidosis type
IVB. This dual disease phenotype reflects the enzyme''s dual substrate specificity.'
- reference_id: web:https://www.ncbi.nlm.nih.gov/books/NBK564432/
supporting_text: Beta-hexosaminidase A forms part of a complex that breaks down
GM2 ganglioside. HEXA variants that cause Tay-Sachs disease eliminate beta-hexosaminidase
A activity, preventing GM2 ganglioside breakdown.
literature_support:
assessment: STRONG
notes: 'All four condition sets have extensive experimental support. Alpha-L-iduronidase
(condition set 2): Over 201 IDUA mutations documented, enzyme replacement therapy
(Aldurazyme) approved, crystal structures solved, dermatan sulfate and heparan
sulfate accumulation demonstrated in MPS I patients. N-acetylglucosamine-6-sulfatase
(condition set 4): GNS mutations cause Sanfilippo D with specific heparan sulfate
accumulation, enzyme assays demonstrate substrate specificity, recombinant enzyme
therapy under development. Beta-galactosidase (condition set 1): GLB1 mutations
cause distinct phenotypes (GM1 gangliosidosis versus MPS IVB) depending on residual
activity toward different substrates, crystal structures explain substrate binding,
enzyme assays confirm dual specificity for GM1 ganglioside and keratan sulfate.
Beta-hexosaminidase (condition set 3): HEXA and HEXB mutations cause Tay-Sachs
and Sandhoff diseases respectively, crystal structures of Hex A and Hex B solved,
substrate specificity for GM2 ganglioside and keratan sulfate experimentally validated.
The literature strongly supports that all four enzymes can hydrolyze bonds in
GAG chains, but also clearly demonstrates that beta-galactosidase and beta-hexosaminidase
have primary roles in ganglioside rather than proteoglycan metabolism.'
supported_by:
- reference_id: web:https://www.ncbi.nlm.nih.gov/books/NBK532261/
supporting_text: Hurler syndrome is caused by deficiency of alpha-L-iduronidase,
resulting in accumulation of dermatan sulfate and heparan sulfate in multiple
tissues with progressive deterioration.
- reference_id: web:https://pubmed.ncbi.nlm.nih.gov/6450420/
supporting_text: Sanfilippo disease type D is caused by deficiency of N-acetylglucosamine-6-sulfate
sulfatase required for heparan sulfate degradation, with accumulation of excessive
heparan sulfate.
- reference_id: web:https://medlineplus.gov/genetics/gene/glb1/
supporting_text: Beta-galactosidase is involved in metabolism of GM1 ganglioside
and keratan sulfate. GLB1-related disorders include GM1 gangliosidosis and mucopolysaccharidosis
type IVB with distinct phenotypes.
- reference_id: web:https://pmc.ncbi.nlm.nih.gov/articles/PMC2910754/
supporting_text: Crystal structure of human beta-hexosaminidase B explains substrate
specificity. HEXB mutations cause Sandhoff disease characterized by GM2 ganglioside
accumulation.
- reference_id: web:https://www.ncbi.nlm.nih.gov/books/NBK579925/
supporting_text: Degradation of GAG chains occurs via sulfatase-catalyzed removal
of terminal sulfate groups and sequential action of exoglycosidases. At least
14 lysosomal storage diseases affect GAG catabolism.
condition_overlap:
assessment: NONE
notes: 'The four condition sets target distinct enzyme families with no sequence
or structural overlap. Condition set 1 targets beta-galactosidase (GLB1, GH35
family), condition set 2 targets alpha-L-iduronidase (IDUA, GH39 family), condition
set 3 targets beta-hexosaminidase (HEXA/HEXB, GH20 family), and condition set
4 targets N-acetylglucosamine-6-sulfatase (GNS, sulfatase family). These represent
independent evolutionary solutions to specific bond cleavage reactions in GAG
degradation. Mechanistically, they cleave different bonds: beta-galactosidase
removes terminal beta-galactose, alpha-L-iduronidase removes alpha-L-iduronate,
beta-hexosaminidase removes N-acetylhexosamine, and GNS removes 6-sulfate from
N-acetylglucosamine. The enzymes act sequentially in lysosomal GAG catabolism
pathways but do not overlap in substrate specificity. However, there is functional
overlap in the sense that beta-galactosidase and beta-hexosaminidase both have
primary roles in ganglioside catabolism, creating a different kind of "overlap"
issue—overlap in biological context rather than molecular specificity.'
go_specificity:
assessment: TOO_BROAD
notes: GO:0030167 (proteoglycan catabolic process) shows variable appropriateness
across the four condition sets. For condition set 2 (alpha-L-iduronidase) and
condition set 4 (N-acetylglucosamine-6-sulfatase), GO:0030167 is highly appropriate
and could potentially be made more specific with child terms like "dermatan sulfate
catabolic process" (GO:1902556) or "heparan sulfate proteoglycan catabolic process"
(GO:0030200). For condition sets 1 (beta-galactosidase) and 3 (beta-hexosaminidase),
GO:0030167 is technically accurate but too broad and potentially misleading—it
fails to capture the primary biological roles of these enzymes in ganglioside
metabolism. More appropriate primary annotations would be "GM1 ganglioside catabolic
process" (GO:0006689) for GLB1 and "ganglioside catabolic process" (GO:0006687)
or "GM2 ganglioside catabolic process" for hexosaminidase. The current annotation
strategy creates a situation where users searching for proteoglycan-degrading
enzymes will retrieve GLB1 and hexosaminidase, potentially not understanding that
these enzymes' primary functions lie elsewhere. A hierarchical annotation approach
with both primary and secondary GO terms would better reflect the biological reality.
supported_by:
- reference_id: web:https://www.ncbi.nlm.nih.gov/books/NBK164500/
supporting_text: MPS IVB is associated with GLB1 variants that impair catalytic
degradation of keratan sulfate while GM1 gangliosidosis is associated with variants
impairing ganglioside degradation, indicating the enzyme's dual substrate specificity.
- reference_id: web:https://pmc.ncbi.nlm.nih.gov/articles/PMC2910754/
supporting_text: Beta-hexosaminidase processes multiple substrate types including
sphingolipids, oligosaccharides, and keratan sulfate, but primary clinical significance
relates to GM2 ganglioside degradation defects causing Tay-Sachs and Sandhoff
diseases.
taxonomic_scope:
assessment: TOO_NARROW
notes: The taxonomic scopes across condition sets are inconsistent and in one case
appear arbitrary. Condition set 1 uses Eukaryota (NCBITaxon:2759), an extremely
broad scope appropriate for the widespread distribution of beta-galactosidase
across eukaryotes. Condition set 2 has no taxonomic restriction, which is appropriate
given IDUA's conservation across animals and potentially other eukaryotes. Condition
set 3 uses Mus (NCBITaxon:862507), restricting to mouse and rat genera—this is
unjustifiably narrow and creates false negatives for the same enzyme function
in other mammals, vertebrates, and potentially all animals. Beta-hexosaminidase
function in keratan sulfate degradation is conserved across mammals at minimum,
and the Mus restriction appears arbitrary or erroneous. Condition set 4 uses Metazoa
(NCBITaxon:33208), which is appropriate for N-acetylglucosamine-6-sulfatase function
in animals. The inconsistency suggests the rule was not designed with systematic
consideration of taxonomic distribution. Condition set 3 should be expanded to
at least Mammalia (40674) or Vertebrata (7742), and ideally the entire rule should
use consistent taxonomic scope logic.
supported_by:
- reference_id: web:https://medlineplus.gov/genetics/gene/glb1/
supporting_text: Beta-galactosidase is a conserved lysosomal enzyme found across
eukaryotes, supporting the Eukaryota scope in condition set 1.
- reference_id: web:https://pmc.ncbi.nlm.nih.gov/articles/PMC2910754/
supporting_text: Beta-hexosaminidase A and B are conserved across mammals with
similar substrate specificity, contradicting the narrow Mus restriction in condition
set 3.
- reference_id: web:https://www.ncbi.nlm.nih.gov/books/NBK579925/
supporting_text: At least 14 lysosomal storage diseases affect GAG catabolism
across animals, supporting broad Metazoa scope for enzymes like GNS in condition
set 4.
confidence: 0.6
references:
- id: file:rules/arba/ARBA00085883/ARBA00085883-deep-research-falcon.md
title: Deep research analysis via Falcon (30 citations)
findings:
- statement: Beta-galactosidase (GLB1) removes terminal β-galactose from keratan
sulfate and oligosaccharides in lysosome, contributing to proteoglycan fragment
trimming, but is multifunctional and primarily associated with GM1 gangliosidosis.
- statement: Alpha-L-iduronidase (IDUA) is strongly diagnostic for HS/DS catabolism,
hydrolyzes terminal α-L-iduronic acid, with no prominent alternative functions.
Deficiency causes MPS I.
- statement: Beta-hexosaminidase A/B (HEXA/HEXB) primarily involved in ganglioside
catabolism; has broad specificity for terminal HexNAc but direct role in proteoglycan
degradation is indirect. Annotation risks overannotation without additional
constraints.
- statement: N-acetylglucosamine-6-sulfatase (GNS) is obligatory for HS proteoglycan
catabolism, removes 6-O-sulfate from terminal GlcNAc. Strongly tied to HS degradation
with no alternative functions. Deficiency causes MPS IIID.
- statement: GO:0030167 appropriate for IDUA and GNS but may be too broad for HEXA/HEXB
without additional evidence. More specific terms recommended when possible (heparan
sulfate catabolic process, dermatan sulfate catabolic process, keratan sulfate
catabolic process).
- id: web:https://www.ncbi.nlm.nih.gov/books/NBK532261/
title: Hurler Syndrome - StatPearls - NCBI Bookshelf
findings:
- statement: Hurler syndrome is an autosomal recessive disorder caused by defective
IDUA gene encoding alpha-L-iduronidase on chromosome 4, resulting in accumulation
of dermatan sulfate and heparan sulfate in multiple tissues.
- id: web:https://pubmed.ncbi.nlm.nih.gov/6450420/
title: 'Sanfilippo disease type D: deficiency of N-acetylglucosamine-6-sulfate sulfatase'
findings:
- statement: Sanfilippo syndrome type D is caused by N-acetylglucosamine-6-sulfate
sulfatase deficiency required for heparan sulfate degradation, with excessive
heparan sulfate accumulation in patient fibroblasts.
- id: web:https://medlineplus.gov/genetics/gene/glb1/
title: 'GLB1 gene: MedlinePlus Genetics'
findings:
- statement: Beta-galactosidase encoded by GLB1 is involved in metabolism of GM1
ganglioside and keratan sulfate. Deficiency causes GM1 gangliosidosis or mucopolysaccharidosis
type IVB depending on substrate specificity of variants.
- id: web:https://www.ncbi.nlm.nih.gov/books/NBK164500/
title: GLB1-Related Disorders - GeneReviews
findings:
- statement: 'GLB1-related disorders comprise two phenotypically distinct diseases:
GM1 gangliosidosis (impaired ganglioside degradation) and MPS IVB (impaired
keratan sulfate degradation), reflecting dual substrate specificity.'
- id: web:https://www.ncbi.nlm.nih.gov/books/NBK564432/
title: Tay-Sachs Disease - StatPearls
findings:
- statement: Beta-hexosaminidase A breaks down GM2 ganglioside in lysosomes. HEXA
variants causing Tay-Sachs disease eliminate enzyme activity, causing GM2 accumulation
and progressive neuronal damage.
- id: web:https://pmc.ncbi.nlm.nih.gov/articles/PMC2910754/
title: Crystal Structure of Human β-Hexosaminidase B
findings:
- statement: Crystal structure explains substrate specificity of beta-hexosaminidase
B (HEXB homodimer) for GM2 ganglioside, oligosaccharides, and keratan sulfate.
Mutations cause Sandhoff disease.
- id: web:https://www.ncbi.nlm.nih.gov/books/NBK579925/
title: Proteoglycans and Sulfated Glycosaminoglycans - Essentials of Glycobiology
findings:
- statement: GAG degradation occurs via sulfatase-catalyzed sulfate removal and
sequential exoglycosidase action. At least 14 lysosomal storage diseases affect
GAG catabolism, including mucopolysaccharidoses.
- id: web:https://www.ncbi.nlm.nih.gov/books/NBK544295/
title: Biochemistry, Glycosaminoglycans - StatPearls
findings:
- statement: Glycosaminoglycans include heparan sulfate, dermatan sulfate, chondroitin
sulfate, and keratan sulfate. Sequential degradation requires specific lysosomal
enzymes; deficiencies cause mucopolysaccharidoses.
supported_by:
- reference_id: web:https://www.ncbi.nlm.nih.gov/books/NBK579925/
supporting_text: All four enzyme families targeted by this rule participate in the
sequential degradation of glycosaminoglycan chains that constitute proteoglycans,
validating the biochemical accuracy of the GO:0030167 annotation.