Structure and Mechanism
Sulf1 and Sulf2 are new members of a superfamily of arylsulfatases, being closely related to arylsulfatase A, B (ARSA; ARSB) and glucosamine 6-sulfatase (G6S). The x-ray crystal structure of neither Sulf1 or Sulf2 has been attempted, but ARSA active site crystal structure was deciphered. In ARSA, the conserved cysteine, which is posttranslationally modified to a C alpha formylglycine (FG) is critical for catalytic activity. In the first step, one of the two oxygens of the aldehyde hydrate attacks the sulfur of the sulfate ester. This leads to a transesterification of the sulfate group onto the aldehyde hydrate. Simultaneously the substrate alcohol is released. In the second step, sulfate is eliminated from the enzyme-sulfate intermediate by an intramolecular rearrangement. The “intramolecular hydrolysis” allows the aldehyde group to be regenerated. The active site of ARSA contains nine conserved residues that were found to be critical for catalytic activity. Some residues, such as Lys123 and Lys302, bind the substrate while others either participate in catalysis directly, such as His125 and Asp281, or indirectly. In addition a magnesium ion is needed to coordinate the oxygen that attacks the sulfur in the first step of sulfate cleavage. The crystal structure and residue mutations need to be performed in Sulf1 and Sulf2 to determine if any differences exist from lysosomal sulfatases.
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