Biochemical and biophysical characterization of a novel plant protein disulfide isomerase

We recently isolated a protein disulfide isomerase PDI from the Rubiaceae coffee family plant Oldenlandia affinis OaPDI and demonstrated that it facilitates the production of disulfideknotted defense proteins called cyclotides. PDIs are major folding catalysts in the eukaryotic ER where they are responsible for formation, breakage, or shuffling of disulfide bonds in substrate polypeptides and are important chaperones in the secretory pathway. Here, we report the first detailed analysis of the oligomerization behavior of a plant PDI, based on characterization of OaPDI using various biochemical and biophysical techniques, including sizeexclusion chromatography, NMR spectroscopy, surface plasmon resonance and atomic force microscopy. In solution at low concentration OaPDI comprises mainly monomers, but fractions of dimers andor higherorder oligomers were observed at increased conditions, raising the possibility that dimerization andor oligomerization could be a mechanism to adapt to the varioussized polypeptide substrates of PDI. Unlike mammalian PDIs, oligomerization of the plant PDI is not driven by the formation of intermolecular disulfide bonds, but by noncovalent interactions. The information derived in this study advances our understanding of the oligomerization behavior of OaPDI in particular but is potentially of broader interest for understanding the mechanism and role of oligomerization, and hence the catalytic and physiological mechanism, of the ubiquitous folding catalyst PDI. © 2008 Wiley Periodicals, Inc. Biopolymers Pept Sci 92: 35–43, 2009.This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymerswiley.com