Although the Hsp90 chaperone family, comprised in humans of four paralogs, Hsp90α, Hsp90β, Grp94 and Trap-1, has important roles in malignancy, the contribution of each paralog to the cancer phenotype is poorly understood. This is in large part because reagents to study paralog-specific functions in cancer cells have been unavailable. Here we combine compound library screening with structural and computational analyses to identify purine-based chemical tools that are specific for Hsp90 paralogs. We show that Grp94 selectivity is due to the insertion of these compounds into a new allosteric pocket. We use these tools to demonstrate that cancer cells use individual Hsp90 paralogs to regulate a client protein in a tumor-specific manner and in response to proteome alterations. Finally, we provide new mechanistic evidence explaining why selective Grp94 inhibition is particularly efficacious in certain breast cancers.

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Highlights d N-glycosylation transforms a chaperone, GRP94, from a folder into a scaffolding protein d These changes are pathologic in nature as they remodel proteome-wide connectivity d The N-glycosylated GRP94 variant is a small and distinct fraction of the GRP94 pool d Proteome dysfunctions mediated by the N-glycosylated GRP94 variant are actionable