3bsqA Introduction

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Sulfatases are enzymes that hydrolyze sulfate ester bonds. Seventeen unique genes encoding sulfatases have been identified in humans. These are categorized as EC 3.1.6. in enzyme classifications. They all participate in metabolic processes [1]. Most of the family members contain a highly conserved cystine (C) residue and a bivalent metal binding site [4]. The majority of sulfatases are located in lysosymes with acidic pH optima (typically between 5 and 5.5). Most of the sulfatases, including Arylsulfatase A (ASA), Arylsulfatase B (ASB) and N-acetylgalactosamine-6-sulfatase (G6S), are water soluble [1].

An examination of sulfatases with defined functions is helpful in appreciation of the diversity of this enzyme family. ASA is a lysosomal enzyme which hydrolyzes cerebroside sulphate. ASB is also a lysosomal enzyme which hydrolyzes the sulphate ester group from N-acetylgalactosamine 4-sulphate group of dermatine sulphate. Arylsulfatase C (ASC) is a microsomal membrane-bound enzyme that hydrolyses 3β-hydroxysteroid sulfates and is hence also known as steroid sulfatase (STS) [ProFinc]. Substrates hydrolysed by sulfatases include cerebroside sulfate, dermatan sulfate, heparin and keratan sulfate, and steroid sulfates [3]. Previous investigations have revealed that arylsulfatases D, E, F, G, H, J and K are localized in ER and golgi compartments of the cell [2,3].

The sulfatase studied in this experiment is arylsulfatase K (ASK) from Bacteroides thetaiotaomicron. A crystal structure has been obtained for this enzyme, but the function and substrates are unknown. Sequence conservation, structural similarity, other proteins that ASK is known to interact with, and the level of conservation of some key residues that may be involved in its catalytic activity, were all examined in this experiment to determine the possible function of ASK.