Biochemistry of Theiler's murine encephalomyelitis virus isolated from acutely infected mouse brain: identification of a previously unreported polypeptide

Abstract

The WW strain of Theiler's murine encephalomyelitis virus (WW-TMEV) was purified from homogenates of acutely infected mouse brain. Infectious WW-TMEV was found to have an estimated sedimentation coefficient of 156 (s20,w) and a density of 1.35 g/cm3 in CsCl. Electron microscopy revealed a homogeneous population of 26-nm nonenveloped particles. Iodination of sodium dodecyl sulfate (SDS)-disrupted virions revealed four major capsid proteins with molecular weights of 58,000, 37,000, 34,000, and 27,000. A 6,000-dalton polypeptide was observed after long exposures of autoradiograms. The 37,000-, 24,000-, 27,000-, and 6,000-dalton polypeptides corresponded to picornaviral VP1, VP2, VP3, and VP4 capsid polypeptides, respectively. Comparison of autoradiograms of virions radiolabeled before and after SDS disruption indicated that the 58,000-dalton protein, VP2, and VP3 preferentially bound 125I under the labeling conditions used. Direct evidence was obtained that VP2 and VP3 were derived from the 58,000-dalton polypeptide by isolation of the 58,000-dalton polypeptide from polyacrylamide gels run under nonreducing conditions and subjecting it to reelectrophoresis under reducing conditions. The effect of trypsin on purified virions and their polypeptides was also investigated. Trypsin-sensitive sites were found in the 58,000-dalton protein, VP1, and VP2. Our results indicate that, in addition to the four typical picornaviral capsid polypeptides, there is a 58,000-dalton polypeptide present in WW-TMEV, which is sensitive to trypsin and can be reduced into two of the capsid proteins, VP2 and VP3.