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Journal of Virology, June 2000, p. 5667-5678, Vol. 74, No. 12
Department of Biochemistry, North Carolina
State University, Raleigh, North Carolina
27695,1 and Department of Structural
Chemistry, Glaxo Wellcome, Inc., Research Triangle Park, North Carolina
27709-33982
Received 23 December 1999/Accepted 18 March 2000
Sindbis virus contains two membrane glycoproteins, E1 and E2, which
are organized into 80 trimers of heterodimers (spikes). These trimers
form a precise T=4 icosahedral protein lattice on the surface of the
virus. Very little is known about the organization of the E1 and E2
glycoproteins within the spike trimer. To gain a better understanding
of how the proteins E1 and E2 are arranged in the virus membrane, we
have used the techniques of limited proteolysis and amino acid chemical
modification in combination with mass spectrometry. We have determined
that at neutral pH the E1 protein regions that are accessible to
proteases include domains 1-21 (region encompassing amino acids 1 to
21), 161-176, and 212-220, while the E2 regions that are accessible
include domains 31-84, 134-148, 158-186, 231-260, 299-314, and
324-337. When Sindbis virus is exposed to low pH, E2 amino acid
domains 99-102 and 262-309 became exposed while other domains became
inaccessible. Many new E1 regions became accessible after exposure to
low pH, including region 86-91, which is in the putative fusion domain of E1 of Semliki Forest virus (SFV) (M. C. Kielian et al., J. Cell
Biol. 134:863-872, 1996). E1 273-287 and region 145-158 were also
exposed at low pH. These data support a model for the structure of the
alphavirus spike in which the E1 glycoproteins are centrally located as
trimers which are surrounded and protected by the E2 glycoprotein.
These data improve our understanding of the structure of the virus
membrane and have implications for understanding the protein
conformational changes which accompany the process of virus-cell
membrane fusion.
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
The Surface Conformation of Sindbis Virus
Glycoproteins E1 and E2 at Neutral and Low pH, as Determined by Mass
Spectrometry-Based Mapping
*
Corresponding author. Mailing address: Campus Box 7622, North Carolina State University, Raleigh, NC 27695-7622. Phone: (919) 515-5802. Fax: (919) 515-2047. E-mail:
Dennis_Brown{at}ncsu.edu.
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