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Front Mol Biosci. 2018 Feb 28;5:18. doi: 10.3389/fmolb.2018.00018. eCollection 2018.

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

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1
Department of Chemistry and Biochemistry, University of Windsor, Windsor, ON, Canada.
2
Laboratory of Molecular and Cellular Biochemistry, Faculty of Life Sciences, Kyoto Sangyo University, Kyoto, Japan.
3
Molecular Profiling Research Center for Drug Discovery, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan.

Abstract

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 reduction of the rate of electron shuttling between PDI and the intraluminal endoplasmic reticulum oxidase, ERO1α, suggesting a functional significance to oxidative protein folding. In light of this, the possibility of lysine acetylation at residues Lys57 and Lys401 was 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 the acetylated protein form nearly mimicked that obtained with a K57/401Q double substitution variant providing an indication that acetylation of the active site-flanking lysine residues can act to reversibly modulate PDI activity.

KEYWORDS:

enzyme kinetics; lysine acetylation; oxidative protein folding; protein disulfide isomerase; redox; thiol-disulfide exchange

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