SARS-CoV-2 membrane protein conformations induce distinct membrane curvatures

The assembly and budding of enveloped viruses requires thousands of membrane proteins to collectively remodel host-cell membranes into highly curved virions. In SARS-CoV-2, this process is driven by interactions between viral structural proteins and the endoplasmic reticulum-Golgi intermediate compartment (ERGIC) membrane. The membrane (M) protein, an embedded homodimer and the most abundant viral component, exists in two conformations: a compact ''short'' form and an elongated ''long'' form. Although M is essential for virion assembly, how its conformations contribute to the generation and organization of the membrane curvature required for budding has remained unknown. Here, we used all-atom and Martini coarse-grained molecular dynamics simulations to show that individual M proteins can induce distinct membrane curvatures, depending on their conformation. The long form bends the membrane around its C-terminal, forming a valley-like depression, while the short form predominantly bends the membrane away from the C-terminal producing an anisotropic ridge. The induced curvatures correspond to the bulb and neck regions of a budding virion, respectively. Coarse-grained simulations of M protein pairs further reveal that curvature modulates long-range, membrane-mediated M-M interactions, leading to repulsion between dissimilar conformations. Together, these results suggest that the long and short forms of M naturally segregate to shape the virion's bulb and neck, potentially facilitating genome encapsulation and membrane scission. This mechanism provides a physical basis for coronavirus budding and suggests that conformationally encoded curvature fields may represent a general principle underlying the formation of enveloped viruses.