Highly versatile small virus-encoded proteins in cellular membranes: A structural perspective on how proteins' inherent conformational plasticity couples with host membranes' properties to control cellular processes.

We investigated several small viral proteins that reside and function in cellular membranes. These proteins belong to the viroporin family because they assemble into ion-conducting oligomers. However, despite forming similar oligomeric structures with analogous functions, these proteins have diverse amino acid sequences. In particular, the amino acid compositions of the proposed channel-forming transmembrane (TM) helices are vastly different-some contain residues (e.g., His, Trp, Asp, Ser) that could facilitate cation transport. Still, other viroporins' TM helices encompass exclusively hydrophobic residues; therefore, it is difficult to explain their channels' activity, unless other mechanisms (e.g., involving a negative lipid headgroups and/or membrane destabilization) take place. For this study, we selected the M2, Vpu, E, p13II, p7, and 2B proteins from the influenza A, HIV-1, human T-cell leukemia, hepatitis C, and picorna viruses, respectively. We provide a brief overview of the current knowledge about these proteins' structures as well as remaining questions about more comprehensive understanding of their structures, conformational dynamics, and function. Finally, we outline strategies to utilize a multi-prong structural and computational approach to overcome current deficiencies in the knowledge about these proteins.