Deduced structural model for animal rhabdovirus glycoproteins

The G protein sequences of fourteen animal rhabdoviruses, representing all four recognized genera (Vesiculovirus, Lyssavirus, Ephemerovirus and Novirh abdovirus) and the ungrouped sigma virus, were aligned using CLUSTAL W and adjusted to account for obvious sequence similarities not detected by the a lgorithm. Analysis of the alignment indicated remarkable preservation of G protein structural features including cysteine residues, antigenic sites an d significant elements of secondary structure (alpha-helices, beta-strands and loops). Twelve highly conserved cysteine residues were assigned numbers (C-I to C-XII) according to their location in the alignment. Other cystein e residues were assigned numbers (C-O to C-XIIe) according to their positio n relative to the conserved cysteines, The pattern of conservation of cyste ine residues and the structural characteristics of identified discontinuous antigenic sites were used to deduce a model for G protein structure. Six a bsolutely conserved cysteines are predicted to associate in three disulphid e bridges (C-I-C-XII; C-VIII-C-XI; C-IX-C-X) that form the core of the G pr otein structure and define the common discontinuous antigenic site. The ass ociations of six other highly conserved cysteines (C-II-C-IV; C-III-C-V; C- VI-C-VII) are predicted by the absence of a specific pair in all viruses wi thin a genus. Of the other cysteines, one pair occurs only in ephemerovirus es and novirhabdoviruses (C-O-C-XIIa); two pairs occur only in ephemeroviru ses (C-Ib-C-VIIIa; C-XIIb-C-XIIe); and two pairs occur only in lyssaviruses (C-Ia-C-VIIIb; C-XIIc-C-XIId). The structures predicted by the model accou nt for the preservation of conformational antigenic sites, accommodate genu s-specific variations, and are generally consistent with previous observati ons of G protein structure.