Abstract
Coronaviruses (CoVs) are enveloped, positive sense, single strand RNA viruses that cause respiratory, intestinal and neurological diseases in mammals and birds. Following replication, CoVs assemble on intracellular membranes including the endoplasmic reticulum Golgi intermediate compartment (ERGIC) where the envelope protein (E) functions in virus assembly and release. In consequence, E potentially contains membrane-modifying peptides. To search for such peptides, the E coding sequence of Mouse Hepatitis Virus (MHV) was inspected for its amino acid conservation, proximity to the membrane and/or predicted amphipathic helices. Peptides identified in silico were synthesized and tested for membrane-modifying activity in the presence of giant unilamellar vesicles (GUVs) consisting of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), sphingomyelin and cholesterol. To confirm the presence of membrane binding peptides identified in the context of a full-length E protein, the wild type and a number of mutants in the putative membrane binding peptide were expressed in Lenti-X-293T mammalian and insect cells, and the distribution of E antigen within the expressing cell was assessed. Our data identify a role for the post-transmembrane region of MHV E in membrane binding.
Highlights
The coronavirus envelope protein (E) is a small hydrophobic protein ranging from 74–109 amino acids [1,2]
Amphipathicity occurred in a region immediately downstream of the TM domain, a region which contains the previously mapped cysteine region [30] at the end of the predicted transmembrane domain (Figure 1) and which is palmitoylated intracellularly [8,31] to facilitate contact with the lipid bilayer [32]
The CoV E proteins consist from a short hydrophilic amino terminal region, a hydrophobic transmembrane region and a carboxy-terminal region that encompasses the majority of the protein [30]
Summary
The coronavirus envelope protein (E) is a small hydrophobic protein ranging from 74–109 amino acids [1,2]. It has an N-terminal domain, a long alpha helical transmembrane domain and a C-terminal hydrophilic domain, and is found incorporated into the virus particles of all coronavirus groups at low levels [3,4,5,6,7]. The membrane curving properties of E are such that the coexpression of M and E is adequate for the efficient formation of virus-like particles (VLP) [11,12], and these can incorporate the S protein if it is coexpressed [13].
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