Mechanistic insights on the reduction of glutathione disulfide by protein disulfide isomerase

• Type: Article in International Scientific Journal
• Date: 2017

Authors

Neves, RPP (Author) FCUP; Pedro A Fernandes (Author) FCUP; Ramos, MJ (Author) FCUP

Journal

Title: Proceedings of the National Academy of Sciences of the United States of America

Vol. 114

ISSN: 0027-8424

Publisher: National Academy of Sciences

Indexing

ISI Web of Knowledge - 40 Citations

Scopus - 44 Citations

Other information

Authenticus ID: P-00N-G9H

DOI: 10.1073/pnas.1618985114

Abstract (EN): We explore the enzymatic mechanism of the reduction of glutathione disulfide (GSSG) by the reduced a domain of human protein disulfide isomerase (hPDI) with atomistic resolution. We use classical molecular dynamics and hybrid quantum mechanics/molecular mechanics calculations at the mPW1N/6-311+G(2d,2p):FF99SB//mPW1N/6-31G(d):FF99SB level. The reaction proceeds in two stages: (i) a thiol-disulfide exchange through nucleophilic attack of the Cys53-thiolate to the GSSG-disulfide followed by the deprotonation of Cys56-thiol by Glu47-carboxylate and (ii) a second thiol-disulfide exchange between the Cys56-thiolate and the mixed disulfide intermediate formed in the first step. The Gibbs activation energy for the first stage was 18.7 kcal.mol(-1), and for the second stage, it was 7.2 kcal.mol(-1), in excellent agreement with the experimental barrier (17.6 kcal.mol(-1)). Our results also suggest that the catalysis by protein disulfide isomerase (PDI) and thiol-disulfide exchange is mostly enthalpy-driven (entropy changes below 2 kcal.mol(-1) at all stages of the reaction). Hydrogen bonds formed between the backbone of His55 and Cys56 and the Cys56-thiol result in an increase in the Gibbs energy barrier of the first thiol-disulfide exchange. The solvent plays a key role in stabilizing the leaving glutathione thiolate formed. This role is not exclusively electrostatic, because an explicit inclusion of several water molecules at the density-functional theory level is a requisite to form the mixed disulfide intermediate. In the intramolecular oxidation of PDI, a transition state is only observed if hydrogen bond donors are nearby the mixed disulfide intermediate, which emphasizes that the thermochemistry of thiol-disulfide exchange in PDI is influenced by the presence of hydrogen bond donors.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 10