Hideaki Itoh

Graduate School and Faculty of Engineering and Resource Science, Akita University, 1-1 Tegata Gakuen Town, Akita City 010-8502, Japan

Abstract:

Although gentamicin (GM) has been used widely as an antibiotic, the specific binding protein of the drug has not yet been understood sufficiently. Here we show that GM specifically associates with the 70-kDa molecular chaperone HSP70 and reduces its chaperone activity in vitro. In the present study, we investigated GM-specific binding proteins using a GM-affinity column and porcine kidney cytosol. After washing the column, only the 70-kDa protein was eluted from the column by the addition of 10 mM GM. None of the other proteins were found in the eluant. Upon immunoblotting, the protein was identical to HSP70. Upon CD spectrum analysis, the binding of GM to HSP70 resulted in a conformational change in the protein. Although HSP70 prevents aggregation of unfolded rhodanese in vitro, the chaperone activity of HSP70 was suppressed in the presence of GM. Using limited proteolysis of HSP70 by TPCK-trypsin, the GM binding site is a COOH-terminal for one third of the protein known to be a peptide-binding domain. During immunohistochemistry, HSP70 and GM were co-localized in enlarged lysosomes of rat kidneys with GM-induced acute tubular injury in vivo. Our results suggest that the specific association between HSP70 and GM may reduce the chaperone activity of HSP70 in vitro and/or in vivo, and this may have an interaction with GM toxicity in kidneys with GM-induced acute tubular injury.

Keywords: 70-kDa molecular chaperone HSP70 and antibiotic gentamicin.