Exploring of the immune-related functions of Glucose regulated protein 94 (GRP94) in Mytilus coruscus

Glucose regulated protein 94 (GRP94) is an endoplasmic reticulum (ER)-resident member of the heat shock protein 90 (HSP90) family that functions as a molecular chaperone. GRP94 had been identified as an immune-related molecule in bivalves. Nevertheless, the functional role of GRP94 in bivalve immunity remains poorly understood. Here, we identified a novel GRP94 from the mussel Mytilus coruscus, designated McGRP94, which contains a signal peptide and a HSP90 domain. We characterized its sequence features and expression patterns, produced recombinant McGRP94 (rMcGRP94) and a corresponding polyclonal antibody, and investigated the in vitro functions of rMcGRP94 along with its transcriptomic effects on hemocytes and mantle tissue. Our results indicate that McGRP94 is highly expressed in hemocytes, gill, and mantle, and responds significantly to microbial challenge. In vitro, rMcGRP94 exhibits weak antimicrobial activity, as well as bacterial binding and agglutination capabilities. Transcriptomic profiling revealed that rMcGRP94 modulates protein homeostasis, ER quality control, and immune regulation, providing mechanistic insights into its role in M. coruscus. Moreover, we identified 45 putative McGRP94-interacting proteins in the mantle tissue, including potential co-chaperones and client proteins, thereby outlining a GRP94-centered protein interaction network, and thus providing new insight into GRP94-mediated immune modulation in M. coruscus. Our findings suggest future research avenues regarding the role of GRP94 in mussel innate immunity.