Type I sulfatases catalyze the hydrolysis of sulfate esters through S-O bond cleavage and possess a catalytically essential formylglycine (FGly) active-site residue that is post-translationally derived from either cysteine or serine. Type I sulfatases are inactivated by aryl sulfamates in a time-dependent, irreversible, and active-site directed manner consistent with covalent modification of the active site. We report a theoretical (SCS-MP2//B3LYP) and experimental study of the uncatalyzed and enzyme-catalyzed hydrolysis of aryl sulfates and sulfamates. In solution, aryl sulfate monoanions undergo hydrolysis by an S(N)2 mechanism whereas aryl sulfamate monoanions follow an S(N)1 pathway with SO2NH as an intermediate; theory traces this difference to the markedly greater stability of SO2NH versus SO3. For Pseudomonas aeruginosa arylsulfatase-catalyzed aryl sulfate hydrolysis, Brønsted analysis (log(V(max)/K(M)) versus leaving group pK(a) value) reveals β(LG) = -0.86 ± 0.23, consistent with an S(N)2 at sulfur reaction but substantially smaller than that reported for uncatalyzed hydrolysis (β(LG) = -1.81). Common to all proposed mechanisms of sulfatase catalysis is a sulfated FGly intermediate. Theory indicates a ≥26 kcal/mol preference for the intermediate to release HSO4(-) by an E2 mechanism, rather than alkaline phosphatase-like S(N)2 substitution by water. An evaluation of the stabilities of various proposed end-products of sulfamate-induced sulfatase inactivation highlights that an imine N-sulfate derived from FGly is the most likely irreversible adduct.

Pseudomonas aeruginosa arylsulfatase catalyses the cleavage of aryl sulfates and is an excellent model for human estrone sulfatase, which is implicated in hormone-dependent breast cancer. Aryl sulfamates are inactivators of sulfatases; however, little is known about their mechanism. We studied the inactivation of Pseudomonas aeruginosa arylsulfatase A by a range of aryl sulfamates, including the clinical agent 667COUMATE (STX64) used to inactivate estrone sulfatase. Inactivation was time dependent, irreversible, and active-site directed, consistent with a covalent modification at the active site. In terms of the kinetic parameters of inactivation k(inact) and K(i), K(i) values are in the micromolar to nanomolar range, and the inactivation half-life is less than 30 s. A Brønsted plot of k(inact)/K(i) has a steep slope (beta(lg) = -1.1), which implies that the transition state for the first irreversible chemical step of inactivation involves a high degree of charge transfer and cleavage of the ArO-S bond. Detection of the released phenol and titration of the residual activity showed the stoichiometry of inactivation to be in the range 3-6, with the greatest values found for the most effective inactivators. Thus, multiple sulfamoylation events appear to occur during the inactivation process. These data provide valuable insight into the mechanism of sulfatase inactivation by sulfamates.

Structure/reactivity and structure/structure correlations of 5 sulfate monoesters and 11 sulfamate esters determined by low temperature X-ray crystallography reveal similar ground state deformations that suggest similar reaction coordinates for sulfuryl and sulfamyl group transfer.