Enzyme Mechanism and Function of a Novel Plant PDI Involved in the Oxidative Folding of Cystine Knot Defense Peptides
Cyclotides are disulfide-rich plant peptides containing a head-to-tail cyclized backbone and a cystine knot formed by three conserved disulfide bonds, which makes them extremely stable molecules. Their native function is believed to be plant defense molecules against insect pests. Besides being explored for their various bioactivities, their use as agrochemicals and as a pharmaceutical drug-scaffold is currently under investigation. Cyclotides are synthesized in plants as larger precursor proteins and although their biosynthesis is so far unknown, they are believed to mature by a combination of oxidative folding of the three disulfide bonds, excision from the precursor and cyclisation .
Auxiliary proteins, such as protein disulfide isomerase (PDI), could be involved in their oxidative folding in vivo. PDI is an oxido-reductase enzyme whose major function is the oxidative folding of polypeptides in the endoplasmic reticulum of eukaryotic cells. The exact mechanism of...
KeywordsDisulfide Bond Protein Disulfide Isomerase Defense Peptide CXXC Motif Redox Potential Measurement
The authors thank all members of our laboratories who have contributed by providing materials or help with experiments or discussions. This work was funded by the Australian Research Council and the University of Queensland.