Abstract
The heat shock protein 70 (Hsp70) molecular chaperone is known to be involved in protein folding and protein translocation across membranes in an ATP-dependent fashion. GrpE, an essential co-chaperone which stimulates ADP/ATP exchange on Hsp70, has been conserved in various bacteria and in mitochondria of eukaryotes. Although higher plant chloroplasts also have been known to possess Hsp70 molecular chaperone system, detailed characterization of co-chaperone proteins acting with chloroplast Hsp70 has not yet been achieved. By analyzing genomic and EST databases of Arabidopsis thaliana, we found two candidate genes potentially encoding chloroplast homologs of GrpE which contained an amino-terminal transit peptide-like domain for chloroplast localization and a mature domain which closely resembled to the cyanobacterial GrpE. Both GrpE homologs are actually localized in the chloroplast stroma evenly and form a protein complex with chloroplast Hsp70. Analysis of knockout mutant and functional cooperation of two chloroplast GrpE are under investigation.
