ARSA (Arylsulfatase A / Cerebroside-sulfatase) — review notes

UniProtKB:P15289, human, HGNC:ARSA. EC 3.1.6.8.

Core biology (grounded in UniProt + cached literature)

ARSA is a lysosomal sulfatase of the glycosphingolipid degradation pathway. It
hydrolytically removes the 3-O-sulfate from sulfatide (3-O-sulfogalactosylceramide,
cerebroside-3-sulfate) to yield galactosylceramide (cerebroside) + sulfate.

• UniProt FUNCTION: "Lysosomal enzyme that catalyzes the hydrolysis of cerebroside-3-sulfate
  (sulfatide) into cerebroside and sulfate, a reaction that requires the activator protein
  saposin B." [file:human/ARSA/ARSA-uniprot.txt]
• Catalytic activity (Rhea:RHEA:21300): an N-acyl-1-beta-D-(3-O-sulfo)-galactosyl-sphing-4-enine
• H2O = a beta-D-galactosyl-(1<->1')-N-acylsphing-4-enine + sulfate + H(+); EC=3.1.6.8.
• Requires saposin B (from PSAP) as a lipid-presenting activator, and the catalytic
  Cα-formylglycine (FGly) at Cys69, generated by SUMF1 in the ER [PMID:9342345, PMID:15962010].
• Cofactor: 1 Ca(2+) per subunit (crystallography) PMID:12888274.
• Localises to lysosome / lysosomal lumen; matures through ER (formylglycine generation) and is
  delivered to lysosomes via the mannose-6-phosphate receptor [PMID:2562955, PMID:9342345].
• Also desulfates other sulfated glycolipids (SM3, seminolipid, SB1a ganglio-series sulfatides);
  "It is probably the sole sphingolipid-sulfatase cleaving the galactosyl-3-sulfate bond"
  PMID:11919180.
• Deficiency causes metachromatic leukodystrophy (MLD) — intralysosomal accumulation of
  cerebroside-3-sulfate, demyelination [UniProt DISEASE].

Curation decisions summary

Molecular function

• GO:0004098 cerebroside-sulfatase activity — the precise MF; supported by IDA (PMID:24294900,
  natural sulfatide substrate), EXP (PMID:10751093), IEA(RHEA/EC). ACCEPT (core MF).
• GO:0004065 arylsulfatase activity — broader parent MF (aryl sulfate ester surrogate substrate
  assay). IBA is well-reviewed phylogenetically; IDA (PMID:25553303) and TAS (PMID:2562955) also
  present. ACCEPT (retain broader family MF; core is the more specific cerebroside-sulfatase term).
• GO:0008484 sulfuric ester hydrolase activity — grandparent MF, IDA from SUMF1/SUMF2 modification
  paper. Correct but general; MARK_AS_OVER_ANNOTATED (subsumed by the two specific sulfatase MFs).
• GO:0005509 calcium ion binding — IDA from crystal structure (1 Ca2+/subunit in active site).
  ACCEPT (real, non-core structural cofactor binding).
• GO:0005515 protein binding — all IPI from HT interactome screens (Stitch-seq, HuRI, splice-iso
  interactome). Uninformative bare protein binding. MARK_AS_OVER_ANNOTATED (policy: not REMOVE).

Biological process

• GO:0030149 sphingolipid catabolic process — IDA. Correct parent BP for sulfatide degradation.
  ACCEPT (core BP).
• GO:0006689 ganglioside catabolic process — IDA (PMID:11919180). ARSA degrades ganglio-series
  sulfatides (SB1a) but true gangliosides carry sialic not sulfate; ARSA's role is on the
  sulfated members. KEEP_AS_NON_CORE (peripheral / adjacent pathway).

Cellular component

• GO:0005764 lysosome (IEA + TAS PMID:2562955), GO:0043202 lysosomal lumen (TAS Reactome),
  GO:0036021 endolysosome lumen (IC PMID:27498570) — all correct site of action. ACCEPT lysosome/
  lumen; endolysosome lumen ACCEPT (site where acid hydrolases are active).
• GO:0005783 endoplasmic reticulum / GO:0005788 ER lumen — transit/maturation compartment
  (formylglycine generation, PMID:9342345). KEEP_AS_NON_CORE.
• GO:0005576 extracellular region, GO:0035578 azurophil granule lumen (Reactome neutrophil
  degranulation), GO:0070062 extracellular exosome (HDA proteomics) — bystander/secretory-proteomics
  locations, not the functional site. MARK_AS_OVER_ANNOTATED.

Core functions chosen

• MF: GO:0004098 cerebroside-sulfatase activity (exact GOA sulfatase MF, most specific)
• BP: GO:0030149 sphingolipid catabolic process (directly_involved_in)
• CC: GO:0043202 lysosomal lumen (located_in)