Structural and Mechanistic Analysis of the Choline Sulfatase from Sinorhizobium melliloti: A Class I Sulfatase Specific for an Alkyl Sulfate Ester.

摘要: Abstract Hydrolysis of organic sulfate esters proceeds by two distinct mechanisms, water attacking at either sulfur (S–O bond cleavage) or carbon (C–O cleavage). In primary and secondary alkyl sulfates, attack is favored, whereas in aromatic sulfates sulfated sugars, preferred. This mechanistic distinction mirrored the classification enzymes that catalyze ester hydrolysis: arylsulfatases (ASs) S–O cleavage sugars arylsulfates, sulfatases break C–O sulfates. Sinorhizobium meliloti choline sulfatase (SmCS) efficiently catalyzes hydrolysis choline-O-sulfate (kcat/KM = 4.8 × 103 s− 1 M− 1) as well arylsulfate 4-nitrophenyl (kcat/KM = 12 s− 1 M− 1). Its 2.8-A resolution X-ray structure shows a buried, largely hydrophobic active site which conserved glutamate (Glu386) plays role recognition quaternary ammonium group substrate. SmCS structurally resembles members alkaline phosphatase superfamily, being most closely related to dimeric ASs tetrameric phosphonate monoester hydrolases. Although > 70% amino acids between protomers align (RMSDs 1.79–1.99 A), oligomeric structures show distinctly different packing protomer–protomer interfaces. The latter also play an important formation. Mutagenesis residues typical for ASs, H218O-labeling studies observation catalytically promiscuous behavior toward phosphoesters confirm close relation superfamily suggest AS with extreme catalytic proficiency.