title: Location and role of free cysteinyl residues in the Sindbis virus E1 and E2 glycoproteins.
abstract: Sindbis virus is a single-stranded positive-sense RNA virus. It is composed of 240 copies of three structural proteins: E1, E2, and capsid. These proteins form a mature virus particle composed of two nested T=4 icosahedral shells. A complex network of disulfide bonds in the E1 and E2 glycoproteins is developed through a series of structural intermediates as virus maturation occurs (M. Mulvey and D. T. Brown, J. Virol. 68:805-812, 1994; M. Carleton et al., J. Virol. 71:1558-1566, 1997). To better understand the nature of this disulfide network, E1 and E2 cysteinyl residues were labeled with iodoacetamide in the native virus particle and analyzed by liquid chromatography-tandem mass spectrometry. This analysis identified cysteinyl residues of E1 and E2, which were found to be label accessible in the native virus particle, as well as those that were either label inaccessible or blocked by their involvement in disulfide bonds. Native virus particles alkylated with iodoacetamide demonstrated a 4-log decrease in viral infectivity. This suggests that the modification of free cysteinyl residues results in the loss of infectivity by destabilizing the virus particle or that a rearrangement of disulfide bonds, which is required for infectivity, is blocked by the modification. Although modification of these residues prevented infectivity, it did not alter the ability of virus to fuse cells after exposure to acidic pH; thus, modification of free cysteinyl residues biochemically separated the process of infection from the process of membrane fusion.
authors.affiliation: North Carolina State University, Department of Molecular and Structural Biochemistry, 128 Polk Hall, Raleigh, NC 27695, USA.
authors.forename: Christopher B
authors.initials: CB
authors.lastname: Whitehurst
authors.forename: Erik J
authors.initials: EJ
authors.lastname: Soderblom
authors.forename: Michelle L
authors.initials: ML
authors.lastname: West
authors.forename: Raquel
authors.initials: R
authors.lastname: Hernandez
authors.forename: Michael B
authors.initials: MB
authors.lastname: Goshe
authors.forename: Dennis T
authors.initials: DT
authors.lastname: Brown
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002213:Capsid / Q000737:chemistry; D002460:Cell Line; D002853:Chromatography, Liquid; D006224:Cricetinae; D003545:Cysteine / Q000737:chemistry*; D004220:Disulfides / Q000737:chemistry; D007460:Iodoacetamide / Q000494:pharmacology; D013058:Mass Spectrometry; D008562:Membrane Glycoproteins / Q000737:chemistry*; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D014759:Viral Envelope Proteins / Q000737:chemistry*
chemical_list: D004220:Disulfides; D008562:Membrane Glycoproteins; D014759:Viral Envelope Proteins; C022012:glycoprotein E1, Sindbis virus; C064950:glycoprotein E2, Sindbis virus; D003545:Cysteine; D007460:Iodoacetamide