Glycoproteins of Venezuelan Equine Encephalitis (VEE) Virus: Molecular Structure and Function in Virus Pathogenicity and Host Immunity
The VEE virus particle contains a ssRNA genome enclosed in an icosahedral capsid and an envelope containing two glycoproteins, E2 (56k daltons, gpF6) and El (50k daltons, gp50). The amino terminal sequences of the envelope proteins have been determined and compared with data for other alphaviruses. The alphavirus glycoproteins share regions of homology, particularly in the conservation of proline and cysteine residues, implying that the three dimensional conformation is conserved. Deletions and amino acid replacements can occur at most locations with the alphavirus glycoproteins indicating that variation within the proteins can be accommodated without destroying biological function. Tryptic map analysis of the two virus glycoproteins shows differing degrees of diversity within the VEE complex, the larger protein being the more variable. Viral neutralization (N) and hemagglutination inhibition (HAI) determinants have been placed on the gp56 VEE/TC-83 protein using monoclonal antibody to purified proteins. Antigenic analysis indicates the presence of at least three antigenic epitopes on gp56 and four on gp50. Biological functions of N and HAI are primarily associated with gp56°, the critical N site. In vivo protection from virus infection is provided by passive immunization with antisera to gp56 and gp50 as well as highly avid monoclonal antibodies to gp56c, gp50b, gp50c, and gp50d. Small amounts c of gp56c antibodies were needed to provide protection, whereas less avid antibodies to other determinants on gp56 and gp50 were less protective. Protection from VEE virus infection appears to be determined by the specificity of antibody to the virion glycoprotein epitope, avidity of the antibody and the ability of the antibody to react with antigenic epitopes proximal to the critical N site.
KeywordsEnvelope Glycoprotein Antigenic Epitope Venezuelan Equine Encephalitis Virus Venezuelan Equine Encephalitis Eastern Equine Encephalitis
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