COXSACKIEVIRUS PROTEIN 2B MODIFIES ENDOPLASMIC-RETICULUM MEMBRANE ANDPLASMA-MEMBRANE PERMEABILITY AND FACILITATES VIRUS RELEASE

Digital-imaging microscopy was performed to study the effect of Coxsac kie B3 virus infection on the cytosolic free Ca2+ concentration and th e Ca2+ content of the endoplasmic reticulum (ER). During the course of infection a gradual increase in the cytosolic free Ca2+ concentration was observed, due to the influx of extracellular Ca2+. The Ca2+ conte nt of the ER decreased in time with kinetics inversely proportional to those of viral protein synthesis. Individual expression of protein 2B was sufficient to induce the influx of extracellular Ca2+ and to rele ase Ca2+ from ER stores. Analysis of mutant 2B proteins showed that bo th a cationic amphipathic alpha-helix and a second hydrophobic domain in 2B were required for these activities. Consistent with a presumed a bility of protein 2B to increase membrane permeability, viruses carryi ng a mutant 2B protein exhibited a defect in virus release. We propose that 2B gradually enhances membrane permeability, thereby disrupting the intracellular Ca2+ homeostasis and ultimately causing the membrane lesions that allow release of virus progeny.