Poster: Organelle Biogenesis

Abs # 1168: A chloroplast-localized protein disulfide isomerase preferentially associates with thylakoids in Arabidopsis

Presenter:	Christopher, David A, dchr@hawaii.edu
Authors	Christopher, David A (A)   Danon, Avihai  (B)   Lu, Dongping  (A)
Affiliations:	(A): University of Hawaii (B): Weizmann Institute of Science

The protein disulfide isomerase (PDI) gene family in Arabidopsis consists of 11 members that differ in polypeptide length from 361 to 566 amino acids, presence of signal peptides, KDEL motifs, and the number and positions of thioredoxin domains. The thioredoxin domains are subdivided into three groups containing either monothiol (PWCARS) or dithiol (PWCghC) motifs or lacking these motifs. PDI's catalyze the reversible formation and isomerization of disulfide bonds necessary for the proper folding, assembly, activity, and secretion of numerous enzymes and structural proteins. PDI's have also evolved novel cellular redox functions, as single enzymes and as subunits of protein complexes in organelles. We have previously shown that a dithiol redox mechanism regulates the interaction of proteins with the 5' untranslated leader of the psbA mRNA in Arabidopsis. Using biochemical, molecular and cellular approaches, we have characterized a chloroplast-localized PDI (55 kDa) that is unevenly distributed between the stroma and thylakoids, being three-fold more abundant in thylakoids. PDI-55 levels increase with light intensity and it assembles into a high molecular weight complex. In vitro translation followed by microsomal membrane processing reactions were further used to distinguish ER-from chloroplast-localized PDIs. These results will provide insights into redox regulatory mechanisms in chloroplasts.