Exploring the Functional Complementation between Grp94 and Hsp90

Abstract

Grp94 and Hsp90 are the ER and cytoplasmic paralog members, respectively, of the hsp90 family of molecular chaperones. The structural and biochemical differences between Hsp90 and Grp94 that allow each paralog to efficiently chaperone its particular set of clients are poorly understood. The two paralogs exhibit a high degree of sequence similarity, yet also display significant differences in their quaternary conformations and ATPase activity. In order to identify the structural elements that distinguish Grp94 from Hsp90, we characterized the similarities and differences between the two proteins by testing the ability of Hsp90/Grp94 chimeras to functionally substitute for the wild-type chaperones in vivo. We show that the N-terminal domain or the combination of the second lobe of the Middle domain plus the C-terminal domain of Grp94 can functionally substitute for their yeast Hsp90 counterparts but that the equivalent Hsp90 domains cannot functionally replace their counterparts in Grp94. These results also identify the interface between the Middle and C-terminal domains as an important structural unit within the Hsp90 family.

Different Grp94 components interact transiently with the myocilin olfactomedin domain in vitro to enhance or retard its amyloid aggregation

“…Hsp90 paralogs, which are expressed in different compartments of the cell 3 , have a client base involved in signaling pathways that control cell homeostasis, growth, proliferation, differentiation, and cell death. For well-studied cytosolic Hsp90 family members, which have >500 known clients 4 , co-chaperone and client binding studies have revealed a case-specific, yet broad interaction surface that recognizes remaining exposed hydrophobic patches of largely-folded or intrinsically disordered clients 3 . By contrast, details of chaperone biology and mechanism of the endoplasmic reticulum (ER)-resident paralog glucose regulated protein 94 (Grp94, Fig.…”

Structural and Functional Analysis of GRP94 in the Closed State Reveals an Essential Role for the Pre-N Domain and a Potential Client-Binding Site

“…In addition to differences in structure and ATP hydrolysis rates, GRP94 lacks the retinue of cochaperones characteristic of cytoplasmic Hsp90. In addition, while some GRP94 domains are able to functionally substitute for their yeast Hsp90 counterparts, the equivalent yeast Hsp90 domains fail to replace their GRP94 counterparts in client maturation assays (Maharaj et al, 2016). These observations suggest that regions of divergence between the chaperones may lead to functional differences that are key to GRP94’s adaptation to the ER.…”

GRP94 Is Involved in the Lipid Phenotype of Brain Metastatic Cells

“…Glycoprotein 96 (gp96, GRP94, Erp99, endoplasmin) is an endoplasmic reticulum (ER) lumen resident protein from the HSP90 family [1,2] that belongs to a set of ER chaperones originally discovered as proteins induced by glucose deprivation [3]. GRP94 often functions as a dimer providing a platform for the assembly, folding or oligomerization of loaded protein cargo [4], and its function is ATP-dependent [5].…”