Computational Evidence for the Catalytic Mechanism of Tyrosylprotein Sulfotransferases: A Density Functional Theory Investigation

Abstract

In this paper we have examined the mechanism of tyrosine <i>O</i>-sulfonation catalyzed by human TPST-2. Our computations, in agreement with Teramoto’s hypothesis, indicate a concerted S_N2-like reaction (with an activation barrier of 18.2 kcal mol^–1) where the tyrosine oxygen is deprotonated by Glu⁹⁹ (base catalyst) and simultaneously attacks as a nucleophile the sulfuryl group. For the first time, using a quantum mechanics protocol of alanine scanning, we identified unequivocally the role of the amino acids involved in the catalysis. Arg⁷⁸ acts as a shuttle that “assists” the sulfuryl group moving from the 3′-phosphoadenosine-5′-phosphosulfate molecule to threonine and stabilizes the transition state (TS) by electrostatic interactions. The residue Lys¹⁵⁸ keeps close the residues participating in the overall H-bond network, while Ser²⁸⁵, Thr⁸¹, and Thr⁸² stabilize the TS via strong hydrogen interactions and contribute to lower the activation barrier