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J. Virol., Jun 1996, 3876-3886, Vol 70, No. 6
FJ van Kuppeveld, JM Galama, J Zoll, PJ van den Hurk and WJ Melchers
Enterovirus protein 2B has been shown to increase plasma membrane
permeability. We have identified a conserved putative amphipathic alpha-
helix with a narrow hydrophilic face and an arrangement of cationic
residues that is typical for the so-called lytic polypeptides. To examine
the functional and structural roles of this putative amphipathic
alpha-helix, we have constructed nine coxsackie B3 virus mutants by
site-directed mutagenesis of an infectious cDNA clone. Six mutants
contained substitutions of the charged residues in the hydrophilic face of
the alpha-helix. Three mutants contained insertions of leucine residues
between the charged residues, causing a disturbance of the amphipathic
character of the alpha-helix. The effect of the mutations on virus
viability was assayed by transfection of cells with copy RNA transcripts.
The effect on positive-strand RNA replication was examined by introduction
of the mutations in a subgenomic luciferase replicon and analysis of
luciferase accumulation following the transfection of BGM cells with RNA
transcripts. It is shown that both the amphipathy of the domain and the
presence of cationic residues in the hydrophilic face of the alpha-helix
are required for virus growth. Mutations that disturbed either one of these
features caused defects in viral RNA synthesis. In vitro translation
reactions and the analysis of viral protein synthesis in vivo demonstrated
that the mutations did not affect synthesis and processing of the viral
polyprotein. These results suggest that a cationic amphipathic alpha-helix
is a major determinant for a function of protein 2B, and possibly its
precursor 2BC, in viral RNA synthesis. The potential role of the
amphipathic alpha-helix in the permeabilization of cellular membranes is
discussed.
Copyright © 1996, American Society for Microbiology
Coxsackie B3 virus protein 2B contains cationic amphipathic helix that is required for viral RNA replication
Department of Medical Microbiology, University of Nijmegen, The Netherlands. KUNAZAG3@CAOS.KUN.NL
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