Experimental and Theoretical Insights into the Mechanisms of Sulfate and Sulfamate Ester Hydrolysis and the End Products of Type I Sulfatase Inactivation by Aryl Sulfamates

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• 作者：Spencer J. Williams ; Emma Denehy ; Elizabeth H. Krenske
• 刊名：Journal of Organic Chemistry
• 出版年：2014
• 出版时间：March 7, 2014
• 年：2014
• 卷：79
• 期：5
• 页码：1995-2005
• 全文大小：538K
• 年卷期：v.79,no.5(March 7, 2014)
• ISSN：1520-6904

文摘

Type I sulfatases catalyze the hydrolysis of sulfate esters through S鈥揙 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_N2 mechanism whereas aryl sulfamate monoanions follow an S_N1 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, Br酶nsted analysis (log(V_max/K_M) versus leaving group pK_a value) reveals 尾_LG = 鈭?.86 卤 0.23, consistent with an S_N2 at sulfur reaction but substantially smaller than that reported for uncatalyzed hydrolysis (尾_LG = 鈭?.81). Common to all proposed mechanisms of sulfatase catalysis is a sulfated FGly intermediate. Theory indicates a 鈮?6 kcal/mol preference for the intermediate to release HSO₄^{鈥?/sup> by an E2 mechanism, rather than alkaline phosphatase-like S_N2 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.}