Table 2. Structurally equivalent active-site residues classified by (putative) function in SGSH and closely homologous sulfatases with known atomic structures.

ASA, arylsulfatase A (also known as human lysosomal cerebroside-3-sulfate 3-sulfohydrolase; Lukatela et al., 1998 ▶); ASB, arylsulfatase B (human lysosomal N-acetylgalactosamine-4-sulfate 4-sulfohydrolase (Bond et al., 1997 ▶); PAS, arylsulfatase from P. aeruginosa (Boltes et al., 2001 ▶); ES, human oestrone/dehydroepiandrosterone sulfatase (Hernandez-Guzman et al., 2003 ▶); GALNS, human lysosomal (N-acetyl)galactosamine-6-sulfatase (Rivera-Coln et al., 2012 ▶); BcPMH, sulfatase/hydrolase from B. caryophylli PG2952 (van Loo et al., 2010 ▶). Sequence identities were calculated for protein sequences using the PROMALS3D server (Pei et al., 2008 ▶) and ClustalW2 (BcPMH; Goujon et al., 2010 ▶). R.m.s.d.s were calculated using Coot. Lys123 (SGSH numbering) and its equivalent residues in homologues also participate in sulfate binding.

Enzyme	SGSH	PAS	ASA	ASB	GALNS	ES	BcPMH
PDB code	4mhx	1hdh	1auk	1fsu	4fdi	1p49	2w8s
Sequence identity (%)	100	22.4	22.2	19.7	22.8	19.1	24.6
R.m.s.d. () (No. of residues)	0.00 (482)	2.17 (341)	2.21 (331)	2.18 (312)	1.97 (336)	1.95 (303)	1.98 (345)
Desulfation	FGly70	FGly51	FGly69	FGly91	FGly79	FGly75	FGly57
Metal	Ca2+	Ca2+	Mg2+ (Ca2+)†	Ca2+	Ca2+	Ca2+	Fe
Metal binding	Asp31	Asp13	Asp29	Asp53	Asp39	Asp35	Asp12
	Asp32	Asp14	Asp30	Asp54	Asp40	Asp36
	Asp273	Asp317	Asp281	Asp300	Asp288	Asp342	Asp324
	Asn274	Asn318	Asn282	Asn301	Asn289	Gln343	His325
FGly binding	Arg74	Arg55	Arg73	Arg95	Arg83	Arg79	Arg61
	Lys123	Lys113	Lys123	Lys145	Lys140	Lys134	Tyr105
	His125	His115	His125	His147	His142	His136	Thr107
Sulfate binding	His181	His211	His229	His242	His236	His290	His218
	Arg282	Lys375	Lys302	Lys318	Lys310	Lys368	Lys337

^†The identity of the divalent cation was later demonstrated to be Ca²⁺ in ASA structures with PDB codes 1n2k and 1n2l (Chruszcz et al., 2003 ▶).