Nucleotide sequence of a wheat cDNA encoding protein disulfide isomerase.

Abstract

PDI (EC 5.3.4.1) is an ER-resident protein involved in the rearrangement of disulfide bonds of secretory proteins. This protein also appears as one of the two subunits of another ER resident protein, prolyl 4-hydroxylase (EC 1.14.11.2), and may be involved in various cellular processes (Noiva and Lennarz, 1992). PDI appears to be very abundant in developing wheat grains (Roden et al., 1982) and was also demonstrated to catalyze intrachain disulfide bond formation in a wheat y-gliadin storage protein (Bulleid and Freedman, 1988). To analyze the expression of PDI in developing grains and to study further its role in the folding and assembly of wheat storage proteins, we have cloned a full-length wheat PDI cDNA by screening a root-tip cDNA library using maize PDI as a DNA probe (Table I). Sequence analysis of the wheat cDNA revealed an open reading frame encoding a protein of 515 amino acids, which also exhibited 96 and 63% amino acid sequence identity with full-length PDI cDNAs from barley (accession No. L33250) and alfalfa (Shorrosh and Dixon, 1991), respectively. The deduced amino acid sequence of the wheat PDI also contained an N-terminal signal peptide of 25 amino acids, two conserved thioredoxin-like active sites, a potential N-linked glycosylation site, as well as a C-terminal KDEL sequence generally present in ER-resident proteins.