Coronaviruses, especially severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), present an ongoing threat to human wellbeing. Consequently, elucidation of molecular determinants of their function and interaction with the host is an important task. Whereas some of the coronaviral proteins are extensively characterized, others remain understudied. Here, we use molecular dynamics simulations to analyze the structure and dynamics of the SARS‐CoV‐2 envelope (E) protein (a viroporin) in the monomeric form. The protein consists of the hydrophobic α‐helical transmembrane domain (TMD) and amphiphilic α‐helices H2 and H3, connected by flexible linkers. We show that TMD has a preferable orientation in the membrane, while H2 and H3 reside at the membrane surface. Orientation of H2 is strongly influenced by palmitoylation of cysteines Cys40, Cys43, and Cys44. Glycosylation of Asn66 affects the orientation of H3. We also observe that the monomeric E protein both generates and senses the membrane curvature, preferably localizing with the C‐terminus at the convex regions of the membrane; the protein in the pentameric form displays these properties as well. Localization to curved regions may be favorable for assembly of the E protein oligomers, whereas induction of curvature may facilitate the budding of the viral particles. The presented results may be helpful for a better understanding of the function of the coronaviral E protein and viroporins in general, and for overcoming the ongoing SARS‐CoV‐2 pandemic.

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Coronaviruses, especially SARS-CoV-2, present an ongoing threat for human wellbeing. Consequently, elucidation of molecular determinants of their function and interaction with host is an important task. Whereas some of the coronaviral proteins are extensively characterized, others remain understudied. Here, we use molecular dynamics simulations to analyze the structure and dynamics of the SARS-CoV-2 envelope protein (E protein, a viroporin) in the monomeric form. The protein consists of three parts: hydrophobic α-helical transmembrane domain (TMD) and amphiphilic α-helices H2 and H3, which are connected by flexible linkers. We show that TMD is tilted in the membrane, with phenylalanines Phe20, Phe23 and Phe26 facing the lumen. H2 and H3 reside at the membrane surface. Orientation of H2 is not affected by glycosylation, but strongly influenced by palmitoylation pattern of cysteines Cys40, Cys43 and Cys44. On the other hand, glycosylation affects the orientation of H3 and prevents its stacking with H2. We also find that the E protein both generates and senses the membrane curvature, preferably localizing with the cytoplasmic part at the convex regions of the membrane. Curvature sensing may be favorable for assembly of the E protein oligomers, whereas induction of curvature may facilitate budding of the viral particles. The presented results may be helpful for better understanding of the function of coronaviral E protein and viroporins in general, and for overcoming the ongoing SARS-CoV-2 pandemic.

Transmembrane ion transport is a key process in living cells. Active transport of ions is carried out by various ion transporters including microbial rhodopsins (MRs). MRs perform diverse functions such as active and passive ion transport, photo-sensing, and others. In particular, MRs can pump various monovalent ions like Na+, K+, Cl−, I−, NO3−. The only characterized MR proposed to pump sulfate in addition to halides belongs to the cyanobacterium Synechocystis sp. PCC 7509 and is named Synechocystis halorhodopsin (SyHR). The structural study of SyHR may help to understand what makes an MR pump divalent ions. Here we present the crystal structure of SyHR in the ground state, the structure of its sulfate-bound form as well as two photoreaction intermediates, the K and O states. These data reveal the molecular origin of the unique properties of the protein (exceptionally strong chloride binding and proposed pumping of divalent anions) and sheds light on the mechanism of anion release and uptake in cyanobacterial halorhodopsins. The unique properties of SyHR highlight its potential as an optogenetics tool and may help engineer different types of anion pumps with applications in optogenetics.

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