Hsp70s and Protein Translocation

Likewise for the ER, it was observed that mutants of BiP that led to cells being temperature-sensitive for growth or the direct depletion of BiP from cells blocked the translocation of a number of ER-destined preproteins and resulted in their accumulation in the cytosol (Vogel etal., 1990). Although the preprotein of invertase was found on the cytosolic face of the ER, its signal sequence was proteolytically removed, indicating that it had most likely engaged with the translocation machinery but could 

While mtHsp70 and BiP are intimately involved in protein translocation, they also act as typical molecular chaperones where they are involved in the folding of newly imported proteins and in stabilizing proteins under conditions of cell or organellar stress (Kang et al., 1990 Gethingand Sambrook, 1992 Voisine etal., 1999 Molinari and Helenius, 2000). 

mtHsp70 and BiP are Concentrated at the Preprotein Exit Sites of Translocation Channels 

Mitochondrial Tim44 is a major binding site for mtHsp70, and a stable complex can be found in the absence of ATP (Kronidou et al., 1994 Rassow et al., 1994 Schneider et al., 1994 Voos et al., 1996). About 2% of total mtHsp70 can be in contact with Tim44, while the remainder is in the soluble portion of the matrix. Tim44 is a peripheral 

It is generally accepted that lumenal Hsp70 proteins bind to preproteins and assist in their translocation across membranes in a process requiring ATP hydrolysis. The mechanism of how Hsp70 exerts its action has been the subject of intense interest (Jensen andjohnson, 1999 Pilon and Schekman, 1999 Herrmann and Neupert, 2000 Matouschek et al., 

---