The role of protein disulfide isomerase for sorting glutelin and prolamin polypeptides in rice.

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Analysis of the full length of cDNA clone encoding 60kDa protein disulfide isomerase (PDI) was done. The 60kDa PDI consists of 511 amino acid residues and it has KDEL sequence as a luminal resitent signal. The genomic analysis of 60 kDa PDI shows that it comprises 10 exons with 9 introns intervals. The novel PDI with 40kDa was also cloned and it consists of 441 amino acid residues and has NDEL sequence as a luminal resident signal. The homology between the two PDIs shows about 40%, but both of them have two thioredoxin binding sites which are present in PDI enzyme. The rice mutant esp2 has no 60kDa PDI and the genetical analysis of Esp genes from allelic lines demonstrates that the Esp gene encodes 60kDa PDI. The enzymatic activities of 60kDa and 40kDa PDIs in a wild and esp2 mutant rices weredetermined ans showed that 60% and 40% of total PDI activities in wild rice comes from 60kDa and 40kD PDIs, respectively, while the 60kDa PDI activity is not seen in the esp2 mutant, meaning that 100% of PDI activity derive from 40kDa PDI alone. The immunolocalization of both PDIs shows that the 60kDa PDI is mainly present in the endpsperm, while the 40kDa PDI both in endosperm and aleurone layer.