Heat shock protein 90 mediates protein-protein interactions between human aminoacyl-tRNA synthetases

Heat shock protein 90 (hsp90) is a molecular chaperone responsible for prot ein folding and maturation in vivo. Interaction of hsp90 with human glutamy l-prolyl-tRNA synthetase (EPRS) was found by genetic screening, co-immunopr ecipitation, and in vitro binding experiments. This interaction was sensiti ve to the hsp90 inhibitor, geldanamycin, and also ATP, suggesting that the chaperone activity of hsp90 is required for interaction with EPRS. Interact ion of EPRS with hsp90 was targeted to the region of three tandem repeats l inking the two catalytic domains of EPRS that is also responsible for the i nteraction with isoleucyl-tRNA synthetase (IRS), Interaction of EPRS and IR S also depended on the activity of hsp90, implying that their association w as mediated by hsp90. EPRS and IRS form a macromolecular protein complex wi th at least six other tRNA synthetases and three cofactors, hsp90 preferent ially binds to most of the complex-forming enzymes rather than those that a re not found in the complex. In addition, inactivation of hsp90 interfered with the in vivo incorporation of the nascent aminoacyl-tRNA synthetases in to the multi-ARS complex. Thus, hsp90 appears to mediate protein-protein in teractions of mammalian tRNA synthetases.