Isolation and characterisation of cDNAs encoding protein disulphide isomerases and cyclophilins in wheat

The enzyme families of protein disulphide isomerases (PDI) and cyclophilins catalyse the isomerisation of disulphide bonds and the rotation of Xaa-Pro peptide bonds in nascent proteins, respectively, making them excellent candidates for regulating the deposition of storage proteins in wheat. This study aimed to isolate and characterise clones encoding cyclophilins and PDIs from a wheat endosperm cDNA library. A number of cDNA clones were isolated, of which three different cDNAs each of PDI and cyclophilin were selected for complete sequencing. The three PDI cDNAs encoded putative protein products of 513 or 516 amino acids, all exhibiting conserved sequences for the N-terminal signal peptide, the two thioredoxin-like domains at the catalytic sites and the C-terminal ER retention signal. The three cyclophilin cDNAs exhibited 68-87% identity to other reported cyclophilins and encoded putative protein products of 171 amino acids containing the conserved tryptophan residue and a 7 amino acid sequence unique to certain plant cyclophilins. The sequence variations within and outside the coding regions of all the cDNAs suggest that both enzymes are encoded by multiple genes. This information will allow further investigations into the roles of these enzymes in storage protein deposition in the developing endosperm and thus in wheat quality