An analysis of mitochondrial transport mechanisms and physiological functions of mammalian molecular chaperone HSP60

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Prokaryotic chaperonin has been well characterized, and the crystal structure of the asymmetric GroEL-GroES-(ADP)_7 chaperonin complex has been shown by Xu et al. On the contrary, biochemical properties of mammalian chaperonin homolog (HSP60/10) have not yet fully understood.We have analyzed binding protein to the signal sequence of HSP60 using signal sequence affinity column chromatography and identified only one protein with molecular mass of 70kDa. The protein was identified as HSP70 on immunoblotting using an antibody against HSP70.We have also investigated import of HSP60 into mitochondria in vivo. The mRNA of HSP60 was.increased in the papilla of water- restricted rat kidneys for 3 or 5 days. On immunoblotting analysis, HSP60 was detected both in cytoplasm and mitochondria of normal rat kidney papilla. Although the quantity of the protein was decreased in the cytoplasm of water-restricted rat kidney papilla, the protein was increased in the mitochondria of the papilla.These results suggested that mammalian molecular chaperon HSP60 is located both in the cytoplasm and mitochondria under normal conditions, and that cytoplasmic HSP60 is imported into mitochondria under severe conditions through cytoplasmic HSP70.