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Front. Mol. Biosci. | doi: 10.3389/fmolb.2018.00018

Conserved Residues Lys57 and Lys401 of Protein Disulfide Isomerase Maintain an Active Site Conformation for Optimal Activity: Implications for Post-translational Regulation

  • 1Chemistry and Biochemistry, University of Windsor, Canada
  • 2Life Sciences, Kyoto Sangyo University, Japan
  • 3Molecular Profiling Research Center for Drug Discovery, National Institute of Advanced Industrial Science and Technology (AIST), Japan

Despite its study since the 1960's, very little is known about the post-translational regulation of the multiple catalytic activities performed by protein disulfide isomerase (PDI), the primary protein folding catalyst of the cell. This work identifies a functional role for the highly conserved CxxC-flanking residues Lys57 and Lys401 of human PDI in vitro. Mutagenesis studies have revealed these residues as modulating the oxidoreductase activity of PDI in a pH-dependent manner. Non-conservative amino acid substitutions resulted in enzyme variants upwards of 7-fold less efficient. This attenuated activity was found to translate into a 2-fold decrease of the rate of electron shuttling between PDI and ERO1α suggesting a functional significance to oxidative protein folding. The possibility of lysine acetylation at residues Lys57 and Lys401 was then assessed by in vitro treatment using acetylsalicylic acid (aspirin). A total of 28 acetyllysine residues were identified, including acLys57 and acLys401. The kinetic behavior of acetylated PDI was nearly identical to that obtained with a K57/401Q double substitution providing a strong indication that acetylation of the active site-flanking lysine residues can act to reversibly modulate PDI activity.

Keywords: lysine acetylation, enzyme kientics, protein disulfide isomerase, Thiol-disulfide exchange, redox, Oxidative protein folding

Received: 17 Nov 2017; Accepted: 09 Feb 2018.

Edited by:

Cesare Indiveri, University of Calabria, Italy

Reviewed by:

Iris Finkemeier, Universität Münster, Germany
Maria A. Vanoni, Università degli Studi di Milano, Italy  

Copyright: © 2018 Caba, Ali Khan, Auld, Ushioda, Araki, Nagata and Mutus. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Bulent Mutus, University of Windsor, Chemistry and Biochemistry, 401 Sunset Ave, Windsor, N9B 3P4, ON, Canada, mutusb@uwindsor.ca