The SARS-CoV-2 membrane protein (M-protein) is the most abundant structural protein. The M-protein 1) helps compose the shell (or capsid) encasing the viral nucleic acid, 2) stabilizes other structural proteins by binding to them, 3) assists in viral budding, and 4) may help in viral entry. Other functions of the M-protein are still being elucidated.

Neuropilin-1 (NRP1) is a transmembrane receptor that is involved in numerous biological processes, including angiogenesis, vascular permeability, axon guidance, and mitochondrial iron transport. In October 2020, NRP1 was first demonstrated to facilitate SARS-CoV-2 entry (J. L. Daly et al., Science 10.1126/science.abd3072 (2020)). After the SARS-CoV-2 Spike protein binds to the endogenous ACE2 receptor, the Spike protein is cleaved into two polypeptides: S1 and S2. The C-end rule motif on the S1 polypeptide binds to NRP1. Inhibition of this interaction reduces viral entry.