Interaction of HSPA5 (Grp78, BIP) with negatively charged phospholipid membranes via oligomerization involving the N-terminal end domain

Abstract

Heat shock proteins (HSPs) are ubiquitous polypeptides expressed in all living organisms that participate in several basic cellular processes, including protein folding, from which their denomination as molecular chaperones originated. There are several HSPs, including HSPA5, also known as 78-kDa glucose-regulated protein (GRP78) or binding immunoglobulin protein (BIP) that is an ER resident involved in the folding of polypeptides during their translocation into this compartment prior to the transition to the Golgi network. HSPA5 is detected on the surface of cells or secreted into the extracellular environment. Surface HSPA5 has been proposed to have various roles, such as receptor-mediated signal transduction, a co-receptor for soluble ligands, as well as a participant in tumor survival, proliferation, and resistance. Recently, surface HSPA5 has been reported to be a potential receptor of some viruses, including the novel SARS-CoV-2. In spite of these observations, the association of HSPA5 within the plasma membrane is still unclear. To gain information about this process, we studied the interaction of HSPA5 with liposomes made of different phospholipids. We found that HSPA5 has a high affinity for negatively charged phospholipids, such as palmitoyl-oleoyl phosphoserine (POPS) and cardiolipin (CL). The N-terminal and C-terminal domains of HSPA5 were independently capable of interacting with negatively charged phospholipids, but to a lesser extent than the full-length protein, suggesting that both domains are required for the maximum insertion into membranes. Interestingly, we found that the interaction of HSPA5 with negatively charged liposomes promotes an oligomerization process via intermolecular disulfide bonds in which the N-terminus end of the protein plays a critical role.

The interaction of heat shock proteins with cellular membranes: a historical perspective

“…The interaction of HSPA5 with artificial lipid bilayers (liposomes) has confirmed membrane insertion, displaying a high affinity for negatively charged phospholipids (Dores-Silva et al 2020b). Both HSPA5 N-terminal and C-terminal domains could independently interact with phospholipid membranes, but not at the same levels as the full-length protein, suggesting that the two regions may be involved in membrane insertion (Dores-Silva et al 2020b).…”

“…However, HSPA5 needs to overcome the ER retention signal (KDEL) to reach the cell surface/extracellular environment, which could be a consequence of ER stress (Zhang et al 2013) or any additional factors. HSPA5 is unlikely to interact with the internal ER membrane because the phospholipid composition of this region does not support membrane insertion (Dores-Silva et al, 2020b). Several domains of HSPA5 have been proposed to be inserted into the plasma membrane, particularly the C-terminus end (Tsai et al 2015;Tseng et al 2019).…”

Review: Vaspin (SERPINA12) Expression and Function in Endocrine Cells

“…Interestingly, Nakatsuka et al showed that vaspin binds GRP78 via the helical domains in the N-terminus and not by the RCL region [ 38 ]; the binding site in GRP78 remains unknown. Nevertheless, the mechanism of signal transduction into the cell is also unknown and probably depends on high GRP78 affinity for negatively charged cell membrane phospholipids [ 53 ]. Vaspin also binds to phospholipids, which play a major role in membrane trafficking [ 54 ].…”

Targeting GRP78 enhances the sensitivity of HOS osteosarcoma cells to pyropheophorbide-α methyl ester-mediated photodynamic therapy via the Wnt/β-catenin signaling pathway

“…In addition to its strong antiapoptotic properties, GRP78 is also closely related to tumor proliferation and survival. Studies have shown that GRP78 is one of the key regulators of tumor resistance and is closely related to tumor recurrence and metastasis [ 13 , 14 ]. The Wnt signaling pathway is a group of signal transduction pathways that includes multiple downstream channels that are stimulated by the binding of ligand proteins to membrane protein receptors.…”