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Papers In Press, published online ahead of print September 10, 2003
Department of Molecular Biology, IBR CONICET UNR, Rosario, Santa Fe S2002LRK
Corresponding Author: cecca{at}arnet.com.ar
Protein import into chloroplasts is postulated to occur with the involvement of molecular chaperones. We have determined that the transit peptide of ferredoxin-NADP(H) reductase precursor binds preferentially to an Hsp70 from chloroplast stroma. To investigate the role of Hsp70 molecular chaperones in chloroplast protein import, we analyzed the import into pea chloroplasts of preproteins with decreased Hsp70 binding affinity in their transit peptides. Our results indicate that the precursor with the lowest affinity for Hsp70 molecular chaperones in its transit peptide was imported to chloroplasts with similar apparent Km as the wild type precursor and a two-fold increase in Vmax. Thus, a strong interaction between chloroplast stromal Hsp70 and the transit peptide seems not to be essential for protein import. These results indicate that in chloroplasts the main unfolding force during protein import may be applied by molecular chaperones other than Hsp70s. Although stromal Hsp70s undoubtedly participate in chloroplast biogenesis, the role of these molecular chaperones in chloroplast protein translocation differs from the one proposed in the mechanisms postulated up to date.
J. Biol. Chem, 10.1074/jbc.M306684200
Submitted on June 24, 2003
Revised on September 9, 2003
Accepted on September 9, 2003
Precursors with altered affinity for Hsp70 in their transit peptides are efficiently imported into chloroplasts
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