Heparan sulfate lysosomal degradation (the mucopolysaccharidoses); IDS/IDUA/SGSH/HGSNAT/NAGLU/GNS/GUSB

Heparan sulfate is degraded in the lysosome by an ordered, strictly sequential exolytic cascade that removes one monosaccharide or sulfate group at a time from the non-reducing end of the chain; each enzyme can act only after the preceding one has exposed its substrate, so a deficiency of any single step blocks the whole pathway and causes a mucopolysaccharidosis (MPS) with lysosomal heparan-sulfate storage. Iduronate-2-sulfatase (IDS) first removes the 2-O-sulfate from a terminal iduronate-2-sulfate; alpha-L-iduronidase (IDUA) then hydrolyses the exposed iduronate; sulfamidase (SGSH) removes the N-sulfate from the terminal N-sulfoglucosamine; the lysosomal-membrane transacetylase HGSNAT then N-acetylates the freed glucosamine (using cytosolic acetyl-CoA) so that alpha-N-acetylglucosaminidase (NAGLU) can hydrolyse it; N-acetylglucosamine-6-sulfatase (GNS) removes a 6-O-sulfate; and beta-glucuronidase (GUSB) hydrolyses the terminal glucuronate — regenerating a substrate for IDS/IDUA as the cycle repeats. The three sulfatases (IDS, SGSH, GNS) additionally require the formylglycine catalytic residue generated by SUMF1. Each enzyme defines a distinct disease: MPS II (IDS, Hunter), MPS I (IDUA, Hurler-Scheie), MPS IIIA (SGSH, Sanfilippo A), MPS IIIC (HGSNAT, Sanfilippo C), MPS IIIB (NAGLU, Sanfilippo B), MPS IIID (GNS, Sanfilippo D) and MPS VII (GUSB, Sly).

MODULE:heparan_sulfate_lysosomal_degradationDRAFTMetabolic Pathwaymodules/heparan_sulfate_lysosomal_degradation.yaml
heparan sulfate proteoglycan catabolic processGO:0030200 glycosaminoglycan catabolic processGO:0006027
GO:0030200
heparan sulfate proteoglycan catabolic process
The module is grounded in heparan sulfate proteoglycan catabolic process (GO:0030200); it covers the ordered lysosomal exolytic degradation of heparan sulfate.
GO:0006027
glycosaminoglycan catabolic process
The pathway is part of lysosomal glycosaminoglycan catabolism (GO:0006027); several enzymes also act on dermatan/chondroitin/keratan sulfate.
Reactome:R-HSA-2024096
HS-GAG degradation
Step order and intermediates follow the human Reactome "HS-GAG degradation" pathway (reactions R-HSA-1678650/1678716/1678708/1678660/1678742/1638032/1678854).
file:human/IDS/IDS-ai-review.yaml
IDS gene review (human)
The iduronate-2-sulfatase step (UniProtKB:P22304, GO:0004423) matches the completed human IDS review.
file:human/IDUA/IDUA-ai-review.yaml
IDUA gene review (human)
The alpha-L-iduronidase step (UniProtKB:P35475, GO:0003940) matches the completed human IDUA review.
file:human/SGSH/SGSH-ai-review.yaml
SGSH gene review (human)
The sulfamidase (N-sulfoglucosamine sulfohydrolase) step (UniProtKB:P51688, GO:0016250) matches the completed human SGSH review.
file:human/HGSNAT/HGSNAT-ai-review.yaml
HGSNAT gene review (human)
The heparan-alpha-glucosaminide N-acetyltransferase step (UniProtKB:Q68CP4, GO:0015019) matches the completed human HGSNAT review.
file:human/NAGLU/NAGLU-ai-review.yaml
NAGLU gene review (human)
The alpha-N-acetylglucosaminidase step (UniProtKB:P54802, GO:0004561) matches the completed human NAGLU review.
file:human/GNS/GNS-ai-review.yaml
GNS gene review (human)
The N-acetylglucosamine-6-sulfatase step (UniProtKB:P15586, GO:0008449) matches the completed human GNS review.
file:human/GUSB/GUSB-ai-review.yaml
GUSB gene review (human)
The beta-glucuronidase step (UniProtKB:P08236, GO:0004566) matches the completed human GUSB review.
8Nodes
7Parts
0Variant Sets
0Variants
7Annotons
6Connections

Derived QC

Recommended-field compliance

100.0% recommended fields populated

All recommended fields populated.

Module deep research

✗ none found

No MODULE:heparan_sulfate_lysosomal_degradation deep-research report alongside the module YAML.

Leaf nodes lacking representative members

✓ every leaf node grounds to a representative protein.

Template conformance

✓ every declared conforms_to bundle matches its template motif.

Function consistency and core coverage

7 gene-function check(s) reflected in core functions · 0 conflict(s) · 7 evidence or coverage gap(s) (14 comparison(s))

Retained noncore functions are reported separately; they do not require promotion to core functions. Support from representative genes does not establish conservation across the whole family. Missing reviews or identifiers leave a claim unverified.

AnnotonParticipantFunctionAssessment
ids_activity IDS (human)
UniProtKB:P22304
Family Representative 		iduronate-2-sulfatase activity
GO:0004423 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
idua_activity IDUA (human)
UniProtKB:P35475
Family Representative 		L-iduronidase activity
GO:0003940 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
sgsh_activity SGSH (human)
UniProtKB:P51688
Family Representative 		N-sulfoglucosamine sulfohydrolase activity
GO:0016250 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
hgsnat_activity HGSNAT (human)
UniProtKB:Q68CP4
Family Representative 		heparan-alpha-glucosaminide N-acetyltransferase activity
GO:0015019 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
naglu_activity NAGLU (human)
UniProtKB:P54802
Family Representative 		alpha-N-acetylglucosaminidase activity
GO:0004561 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
gns_activity GNS (human)
UniProtKB:P15586
Family Representative 		N-acetylglucosamine-6-sulfatase activity
GO:0008449 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
gusb_activity GUSB (human)
UniProtKB:P08236
Family Representative 		beta-glucuronidase activity
GO:0004566 		Core Supported
The GO molecular function is reflected in core_functions (exact term or a reviewed subclass).
ids_activity Sulfatase family (IDS)
PANTHER:PTHR45953
Family 		iduronate-2-sulfatase activity
GO:0004423 		Family Function Unreviewed
The family review has no applicable adjudication supporting or excluding GO:0004423.
idua_activity Glycosyl hydrolase 39 family (IDUA)
PANTHER:PTHR12631
Family 		L-iduronidase activity
GO:0003940 		Family Review Missing
No supported structured family review is available for PANTHER:PTHR12631.
sgsh_activity Sulfatase family (SGSH)
PANTHER:PTHR43108
Family 		N-sulfoglucosamine sulfohydrolase activity
GO:0016250 		Family Review Missing
No supported structured family review is available for PANTHER:PTHR43108.
hgsnat_activity HGSNAT transmembrane acetyltransferase family
PANTHER:PTHR31061
Family 		heparan-alpha-glucosaminide N-acetyltransferase activity
GO:0015019 		Family Review Missing
No supported structured family review is available for PANTHER:PTHR31061.
naglu_activity Glycosyl hydrolase 89 family (NAGLU)
PANTHER:PTHR12872
Family 		alpha-N-acetylglucosaminidase activity
GO:0004561 		Family Review Missing
No supported structured family review is available for PANTHER:PTHR12872.
gns_activity Sulfatase family (GNS)
PANTHER:PTHR43108
Family 		N-acetylglucosamine-6-sulfatase activity
GO:0008449 		Family Review Missing
No supported structured family review is available for PANTHER:PTHR43108.
gusb_activity Glycosyl hydrolase 2 family (GUSB)
PANTHER:PTHR10066
Family 		beta-glucuronidase activity
GO:0004566 		Family Review Missing
No supported structured family review is available for PANTHER:PTHR10066.

Gene-review completeness (7/7 grounded genes reviewed)

7 complete review(s) · 0 with deep research · 0 missing review · 7 reviewed but lacking deep research

Gene Review Complete Deep research
GNS P15586 ✓ ✓ ✗
GUSB P08236 ✓ ✓ ✗
HGSNAT Q68CP4 ✓ ✓ ✗
IDS P22304 ✓ ✓ ✗
IDUA P35475 ✓ ✓ ✗
NAGLU P54802 ✓ ✓ ✗
SGSH P51688 ✓ ✓ ✗

Details

Context
lysosomal lumenGO:0043202 lysosomal membraneGO:0005765
Heparan sulfate lysosomal degradationMetabolic Pathwayheparan_sulfate_lysosomal_degradation
heparan sulfate proteoglycan catabolic processGO:0030200 glycosaminoglycan catabolic processGO:0006027
Context
lysosomal lumenGO:0043202 lysosomal membraneGO:0005765

Heparan sulfate lysosomal degradation, grounded to the human enzymes IDS (UniProtKB:P22304, GO:0004423, EC 3.1.6.13), IDUA (P35475, GO:0003940, EC 3.2.1.76), SGSH (P51688, GO:0016250, EC 3.10.1.1), HGSNAT (Q68CP4, GO:0015019, EC 2.3.1.78), NAGLU (P54802, GO:0004561, EC 3.2.1.50), GNS (P15586, GO:0008449, EC 3.1.6.14) and GUSB (P08236, GO:0004566, EC 3.2.1.31). GO molecular-function/BP/location terms were taken from the completed human gene reviews and verified against the local go.db; Reactome reaction ids/titles were verified against the local reactome cache. Each step uses a PANTHER family selector with the human enzyme as representative. The pathway is a strictly ordered exolytic cascade acting from the non-reducing end: every step depends on the product of the previous one, which is why a single enzyme deficiency blocks the whole pathway (the biochemical basis of the mucopolysaccharidoses). Six enzymes are soluble lysosomal-lumen hydrolases/sulfatases; HGSNAT is uniquely a polytopic lysosomal-membrane transacetylase that uses cytosolic acetyl-CoA. The three sulfatases (IDS, SGSH, GNS) require the formylglycine catalytic residue generated by the activating enzyme SUMF1 (a separate gene). Upstream, heparan sulfate proteoglycans are delivered to the lysosome; several of these enzymes also degrade dermatan, chondroitin or keratan sulfate (GALNS, ARSB, GLB1 act in those parallel GAG pathways — separate/overlapping modules; ARSB already reviewed). Disorders: MPS II (IDS), MPS I (IDUA), MPS IIIA (SGSH), MPS IIIC (HGSNAT), MPS IIIB (NAGLU), MPS IIID (GNS) and MPS VII (GUSB).

Connections

ids_step -> idua_step Provides Input For
IDS desulfation of terminal iduronate-2-sulfate exposes iduronate for IDUA.
idua_step -> sgsh_step Provides Input For
IDUA removal of iduronate exposes the N-sulfoglucosamine for SGSH.
sgsh_step -> hgsnat_step Provides Input For
SGSH N-desulfation gives a free-amino glucosamine that HGSNAT N-acetylates.
hgsnat_step -> naglu_step Provides Input For
HGSNAT N-acetylation gives the alpha-N-acetylglucosamine that NAGLU hydrolyses.
naglu_step -> gns_step Provides Input For
NAGLU removal of N-acetylglucosamine exposes the GlcNAc-6-sulfate for GNS.
gns_step -> gusb_step Provides Input For
GNS 6-desulfation exposes the terminal glucuronate for GUSB.
Part 1: iduronate 2-desulfation
removal of 2-O-sulfate from terminal iduronate-2-sulfateReactionids_step

Annotons

IDS: iduronate-2-sulfatase
ids_activity
Participant: Family: Sulfatase family (IDS)
Family:
Sulfatase family (IDS)PANTHER:PTHR45953
Representative Members: IDS (human)UniProtKB:P22304

Function

iduronate-2-sulfatase activityGO:0004423
Substrates: heparan sulfate (terminal iduronate-2-sulfate)
Products: heparan sulfate (terminal iduronate) sulfate

Locations

lysosomal lumenGO:0043202

Deficiency = MPS II (Hunter syndrome), X-linked.

Part 2: iduronate hydrolysis
hydrolysis of terminal alpha-L-iduronateReactionidua_step

Annotons

IDUA: alpha-L-iduronidase
idua_activity
Participant: Family: Glycosyl hydrolase 39 family (IDUA)
Family:
Glycosyl hydrolase 39 family (IDUA)PANTHER:PTHR12631
Representative Members: IDUA (human)UniProtKB:P35475

Function

L-iduronidase activityGO:0003940
Substrates: heparan sulfate (terminal alpha-L-iduronate)
Products: L-iduronate shortened heparan sulfate chain

Locations

lysosomal lumenGO:0043202

Deficiency = MPS I (Hurler, Hurler-Scheie, Scheie).

Part 3: glucosamine N-desulfation
removal of N-sulfate from terminal N-sulfoglucosamineReactionsgsh_step

Annotons

SGSH: sulfamidase (heparan-N-sulfatase)
sgsh_activity
Participant: Family: Sulfatase family (SGSH)
Family:
Sulfatase family (SGSH)PANTHER:PTHR43108
Representative Members: SGSH (human)UniProtKB:P51688

Function

N-sulfoglucosamine sulfohydrolase activityGO:0016250
Substrates: heparan sulfate (terminal N-sulfoglucosamine)
Products: heparan sulfate (terminal glucosamine, free amino group) sulfate

Locations

lysosomal lumenGO:0043202

Deficiency = MPS IIIA (Sanfilippo A).

Part 4: glucosamine N-acetylation (membrane transacetylase)
N-acetylation of terminal alpha-glucosamine (from acetyl-CoA)Reactionhgsnat_step

Annotons

HGSNAT: heparan-alpha-glucosaminide N-acetyltransferase
hgsnat_activity
Participant: Family: HGSNAT transmembrane acetyltransferase family
Family:
HGSNAT transmembrane acetyltransferase familyPANTHER:PTHR31061
Representative Members: HGSNAT (human)UniProtKB:Q68CP4

Function

heparan-alpha-glucosaminide N-acetyltransferase activityGO:0015019
Substrates: heparan sulfate (terminal alpha-glucosamine) acetyl-CoA (cytosolic)
Products: heparan sulfate (terminal alpha-N-acetylglucosamine) CoA

Locations

lysosomal membraneGO:0005765

Deficiency = MPS IIIC (Sanfilippo C).

Part 5: N-acetylglucosamine hydrolysis
hydrolysis of terminal alpha-N-acetylglucosamineReactionnaglu_step

Annotons

NAGLU: alpha-N-acetylglucosaminidase
naglu_activity
Participant: Family: Glycosyl hydrolase 89 family (NAGLU)
Family:
Glycosyl hydrolase 89 family (NAGLU)PANTHER:PTHR12872
Representative Members: NAGLU (human)UniProtKB:P54802

Function

alpha-N-acetylglucosaminidase activityGO:0004561
Substrates: heparan sulfate (terminal alpha-N-acetylglucosamine)
Products: N-acetylglucosamine shortened heparan sulfate chain

Locations

lysosomal lumenGO:0043202

Deficiency = MPS IIIB (Sanfilippo B).

Part 6: N-acetylglucosamine 6-desulfation
removal of 6-O-sulfate from terminal GlcNAc-6-sulfateReactiongns_step

Annotons

GNS: N-acetylglucosamine-6-sulfatase
gns_activity
Participant: Family: Sulfatase family (GNS)
Family:
Sulfatase family (GNS)PANTHER:PTHR43108
Representative Members: GNS (human)UniProtKB:P15586

Function

N-acetylglucosamine-6-sulfatase activityGO:0008449
Substrates: heparan sulfate (terminal GlcNAc-6-sulfate)
Products: heparan sulfate (terminal N-acetylglucosamine) sulfate

Locations

lysosomal lumenGO:0043202

Deficiency = MPS IIID (Sanfilippo D).

Part 7: glucuronate hydrolysis
hydrolysis of terminal beta-D-glucuronateReactiongusb_step

Annotons

GUSB: beta-glucuronidase
gusb_activity
Participant: Family: Glycosyl hydrolase 2 family (GUSB)
Family:
Glycosyl hydrolase 2 family (GUSB)PANTHER:PTHR10066
Representative Members: GUSB (human)UniProtKB:P08236

Function

beta-glucuronidase activityGO:0004566
Substrates: heparan sulfate (terminal beta-D-glucuronate)
Products: D-glucuronate shortened heparan sulfate chain

Locations

lysosomal lumenGO:0043202

Deficiency = MPS VII (Sly syndrome).