Coronavirus envelope protein: a small membrane protein with multiple functions

Coronavirus envelope protein is a small membrane protein and minor component of the virus particles. It plays important roles in virion assembly and morphogenesis, alteration of the membrane permeability of host cells and virus-host cell interaction. Here we review recent progress in characterization of the biochemical properties, membrane topology and functions of the protein.

Biochemical evidence for the presence of mixed membrane topologies of the severe acute respiratory syndrome coronavirus envelope protein expressed in mammalian cells

Coronavirus envelope (E) protein is a small integral membrane protein with multi‐functions in virion assembly, morphogenesis and virus–host interaction. Different coronavirus E proteins share striking similarities in biochemical properties and biological functions, but seem to adopt distinct membrane topology. In this report, we study the membrane topology of the SARS‐CoV E protein by immunofluorescent staining of cells differentially permeabilized with detergents and proteinase K protection assay. It was revealed that both the N‐ and C‐termini of the SARS‐CoV E protein are exposed to the cytoplasmic side of the membranes (N_cytoC_cyto). In contrast, parallel experiments showed that the E protein from infectious bronchitis virus (IBV) spanned the membranes once, with the N‐terminus exposed luminally and the C‐terminus exposed cytoplasmically (N_exo(lum)C_cyto). Intriguingly, a minor proportion of the SARS‐CoV E protein was found to be modified by N‐linked glycosylation on Asn 66 and inserted into the membranes once with the C‐terminus exposed to the luminal side. The presence of two distinct membrane topologies of the SARS‐CoV E protein may provide a useful clue to the pathogenesis of SARS‐CoV.

Biochemical and functional characterization of the membrane association and membrane permeabilizing activity of the severe acute respiratory syndrome coronavirus envelope protein

A diverse group of cytolytic animal viruses encodes small, hydrophobic proteins to modify host cell membrane permeability to ions and small molecules during their infection cycles. In this study, we show that expression of the SARS-CoV E protein in mammalian cells alters the membrane permeability of these cells. Immunofluorescent staining and cell fractionation studies demonstrate that this protein is an integral membrane protein. It is mainly localized to the ER and the Golgi apparatus. The protein can be translocated to the cell surface and is partially associated with lipid rafts. Further biochemical characterization of the protein reveals that it is posttranslationally modified by palmitoylation on all three cysteine residues. Systematic mutagenesis studies confirm that the membrane permeabilizing activity of the SARS-CoV E protein is associated with its transmembrane domain.

Optical modulation and detection in slotted Silicon waveguides

We demonstrate a novel mechanism for low power optical detection and modulation in a slotted waveguide geometry filled with nonlinear electro-optic polymers. The nanoscale confinement of the optical mode, combined with its close proximity to electrical contacts, enables the direct conversion of optical energy to electrical energy, without external bias, via optical rectification, and also enhances electro-optic modulation. We demonstrate this process for power levels in the sub-milliwatt regime, as compared to the kilowatt regime in which optical nonlinear effects are typically observed at short length scales. Our results suggest that a new class of detectors based on nonlinear optics may be practical.

Expression of SARS-coronavirus envelope protein in Escherichia coli cells alters membrane permeability

To promote viral entry, replication, release, and spread to neighboring cells, many cytolytic animal viruses encode proteins responsible for modification of host cell membrane permeability and for formation of ion channels in host cell membranes during their life cycles. In this study, we show that the envelope (E) protein of severe acute respiratory syndrome-associated coronavirus can induce membrane permeability changes when expressed in Escherichia coli. E protein expressed in bacterial and mammalian cells under reducing conditions existed as monomers, but formed homodimer and homotrimer under non-reducing conditions. Site-directed mutagenesis studies revealed that two cysteine residues of the E protein were essential for oligomerization, leading to induction of membrane permeability. This is the first report demonstrating that a coronavirus-encoded protein could modify membrane permeability in E. coli cells.

Comments on “Bubble motion in aqueous surfactant solutions”

The numerical simulations of bubble motion in dilute surfactant solutions reported previously by two of the authors contained a serious numerical inaccuracy. In agreement with experiments, single bubbles released from rest were predicted to reach a maximum speed before slowing to a terminal speed. However, subsequent experiments demonstrated that, in the simulations, the bubbles reached their terminal speed too quickly. The source of the discrepancy is an inaccuracy associated with the numerical algorithm used to solve the surfactant transport equation on the bubble surface. After correcting the problem, the simulations agree much better with the experiments.

Myosin-induced autoimmune myocarditis in BALB/C mice

Experimental mice were immunized with cardiac myosin and complete Freund's adjuvant (CFA) on days 0, 7 and 30 and control mice were immunized with CFA. Sera and myocardium samples were harvested on days 15, 21 and 120 after the first immunization. Pathological findings demonstrated that there were necrosis and inflammatory infiltration in acute stage and fibrosis mainly in chronic stage of experimental group. Anti-myosin antibodies were also found in sera of experimental mice, but not in control group. Our study showed that cardiac myosin served as an autoantigen to provoke autoimmunity and lead to the transformation of VMC into DCM.