GNS (N-acetylglucosamine-6-sulfatase) — review notes

UniProtKB: P15586 (GNS_HUMAN). HGNC:4422. Gene on chromosome 12. EC=3.1.6.14.
552 aa precursor; signal peptide 1-36; mature chain 37-552.

Core biology (verified)

Molecular function. Lysosomal exo-sulfatase that hydrolytically removes the
6-O-sulfate group from terminal N-acetyl-D-glucosamine-6-sulfate (GlcNAc-6-S) residues
of heparan sulfate and keratan sulfate. UniProt FUNCTION: "Hydrolyzes 6-sulfate groups
in N-acetyl-d-glucosaminide units of heparin sulfate and keratan sulfate"
[file:human/GNS/GNS-uniprot.txt]. EC 3.1.6.14, catalytic activity established
PMID:1463457. GO:0008449 N-acetylglucosamine-6-sulfatase activity is the exact,
current MF term carried by GOA (EXP/IDA/IBA/IEA/TAS) and its GO definition matches this
reaction verbatim.
Catalytic mechanism / PTM. Sulfatase-family member; requires the C-alpha-formylglycine
(3-oxoalanine, "FGly") residue generated from the active-site cysteine (Cys91 in the
precursor numbering) by SUMF1 (formylglycine-generating enzyme). UniProt: "The conversion
to 3-oxoalanine ... is critical for catalytic activity" [file:human/GNS/GNS-uniprot.txt].
Binds 1 Ca2+ per subunit. SUMF1/SUMF2 regulate GNS activity PMID:15962010.
Catalytic properties. Human liver enzyme is a highly specific exo-enzyme for
glucosamine-6-sulfate / glucose-6-sulfate residues; forms A and B desulfate keratan-
sulfate- and heparin-derived substrates; no activity toward internal sulfate ester bonds
[PMID:3689315, "Both forms A and B are exo-enzymes, since activity towards internal
sulphate ester bonds was not observed."].
Biological process. Acts in the stepwise exolytic lysosomal catabolism of heparan
sulfate and keratan sulfate (glycosaminoglycan catabolism). PMID:1463457:
"Glucosamine-6-sulphatase is an exo-hydrolase required for the lysosomal degradation of
heparan sulphate and keratan sulphate."
Localization. Lysosome / lysosomal lumen (UniProt SUBCELLULAR LOCATION: Lysosome).
Also detected biochemically in neutrophil primary (azurophil) granules PMID:15595925
and in secreted/exosome fractions (large-scale proteomics) PMID:23533145 — these are
secondary/context locations, not the core catabolic compartment.

Disease

Deficiency causes mucopolysaccharidosis type IIID (MPS IIID; Sanfilippo syndrome D;
MIM 252940), an autosomal-recessive lysosomal storage disorder with heparan-sulfate
accumulation and progressive CNS degeneration [PMID:12573255; PMID:20232353;
file:human/GNS/GNS-uniprot.txt DISEASE].

Annotation review decisions

GO:0008449 (MF, N-acetylglucosamine-6-sulfatase activity) — CORE. All 5 lines (EXP
PMID:1463457; IDA PMID:15595925; IBA; IEA GO_REF:0000120; TAS Reactome + PMID:3689315)
ACCEPT.
GO:0008484 (MF, sulfuric ester hydrolase activity, IDA PMID:15962010) — parent of the
specific sulfatase activity; MODIFY -> GO:0008449 (paper tested GNS among sulphatases
whose activity is FGly/SUMF1-dependent).
GO:0005515 (MF, protein binding, IPI PMID:17474147, NCK1/SH3 peptide array) — bare
"protein binding", high-throughput; MARK_AS_OVER_ANNOTATED.
GO:0005539 glycosaminoglycan binding, GO:0043199 sulfate binding (IEA ortholog) —
substrate-related binding inherent to catalysis; KEEP_AS_NON_CORE (not separately
informative beyond the enzyme activity).
GO:0030200 heparan sulfate proteoglycan catabolic process (IBA + IDA + IEA) — CORE BP,
ACCEPT. GO:0006027 glycosaminoglycan catabolic process (TAS) ACCEPT (parent-level, valid).
GO:0042340 keratan sulfate proteoglycan catabolic process (IEA) ACCEPT (UniProt/EC name
both substrates). GO:0030203 glycosaminoglycan metabolic process (IEA InterPro) — broad
metabolic parent; KEEP_AS_NON_CORE.
CC lysosome (IBA is_active_in, IEA) + lysosomal lumen (TAS) — CORE, ACCEPT.
CC azurophil granule / azurophil granule lumen / ficolin-1-rich granule lumen /
extracellular region / extracellular exosome — secondary neutrophil-granule/secreted
locations; KEEP_AS_NON_CORE.

Core MF term used in core_functions

GO:0008449 "N-acetylglucosamine-6-sulfatase activity" (exact current GOA term).