Interaction of heat stress glycoprotein GP50 with classical heat-shock proteins

Cellular stress conditions are known to elevate heat-shock protein (HSP) synthesis and protein glycosylation, leading to the development of cellular thermotolerance. In the present study, we investigated the interaction of a major stress glycoprotein, GP50, with other cellular proteins during recovery from heat stress, using' mostly immunoprecipitation techniques. Parallel studies of heat-stressed CHO and M21 cells showed that both glycosylated and unglycosylated forms of GP50 interact with several members of the classical HSP families (e.g., HSP70 and HSP90) in an ATP-dependent manner. The specificity of HSP-stress glycoprotein interactions was confirmed by chemical crosslinking with a homobifunctional agent, 3,3'-dithiobis (succinimidyl propionate). Interaction of GP50 with denatured proteins was also demonstrated through binding to gelatin. Protein complexes formed between stress glycoproteins and HSPs were further characterized by gel filtration and showed an average molecular mass between 400 and 600 kDa. Overall, the consistent association of stress glycoproteins with nonglycosylated HSPs suggests a structural/functional role for protein chaperone complexes that consist of denatured proteins and the glycone/aglycone elements of cellular stress response.