A novel plant protein-disulfide isomerase involved in the oxidative folding of cystine knot defense proteins.
We have isolated a protein-disulfide isomerase (PDI) from Oldenlandia affinis (OaPDI), a coffee family (Rubiaceae) plant that accumulates knotted circular proteins called cyclotides. The novel plant PDI appears to be involved in the biosynthesis of cyclotides, since it co-expresses and interacts with the cyclotide precursor protein Oak1. OaPDI exhibits similar isomerase activity but greater chaperone activity than human PDI. Since domain c of OaPDI is predicted to have a neutral pI, we conclude that this domain does not have to be acidic in nature for PDI to be a functional chaperone. Its redox potential of -157 +/- 4 mV supports a role as a functional oxidoreductase in the plant. The mechanism of enzyme-assisted folding of plant cyclotides was investigated by comparing the folding of kalata B1 derivatives in the presence and absence of OaPDI. OaPDI dramatically enhanced the correct oxidative folding of kalata B1 at physiological pH. A detailed investigation of folding intermediates suggested that disulfide isomerization is an important role of the new plant PDI and is an essential step in the production of insecticidal cyclotides. The nucleotide sequence(s) reported in this paper have been submitted to the GenBank/EBI Data Bank with accession number(s) 911777.
Gruber
Christian W
CW
Institute for Molecular Bioscience, University of Queensland, Brisbane, Queensland 4072, Australia.
Cemazar
Masa
M
Clark
Richard J
RJ
Horibe
Tomohisa
T
Renda
Rosemary F
RF
Anderson
Marilyn A
MA
Craik
David J
DJ
D019943:Amino Acid Substitution; D047169:Cyclotides / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics; D047168:Cystine Knot Motifs / Q000502:physiology; D004220:Disulfides / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007306:Insecticides / Q000737:chemistry / Q000378:metabolism; D018832:Molecular Chaperones / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D032067:Oldenlandia / Q000201:enzymology* / Q000235:genetics; D010084:Oxidation-Reduction; D010456:Peptides, Cyclic / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics; D010940:Plant Proteins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics; D019704:Protein Disulfide-Isomerases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017510:Protein Folding
D047169:Cyclotides; D004220:Disulfides; D007306:Insecticides; D018832:Molecular Chaperones; C437886:OAK1 protein, Oldenlandia affinis; D010456:Peptides, Cyclic; D010940:Plant Proteins; C091930:kalata B1; D019704:Protein Disulfide-Isomerases