Role of Heat Shock Proteins in Mitochondrial Protein Import
Most proteins destined for cell organelles are synthesized on cytosolic polysomes and must cross one or more organelle membranes to reach their functional destination (Wickner and Lodish, 1985). With mitochondria, over 95% of the proteins are made as precursor proteins in the cytosol and are mainly post-translationally imported into the four mitochondrial subcompartments (outer membrane, intermembrane space, inner membrane, and matrix) (Attardi and Schatz, 1988; Hartl and Neupert, 1990; Pfanner and Neupert, 1990). Heat shock proteins (hsps) were found to play an important role at various stages of mitochondrial protein import. This includes the maintenance of a transport-competent conformation of precursor proteins by cytosolic hsp70s (Deshaies etal., 1988; Murakami etal., 1988; Pfanner etal., 1990), the involvement of mitochondrial HSP70 in translocation of precursor proteins through contact sites between mitochondrial outer and inner membranes (Kang etal., 1990), and the refolding of imported proteins at HSP60 in the mitochondrial matrix (Ostermann etal., 1989).
KeywordsHydrolysis Polypeptide Cytosol Sorting Nucleoside
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