Mutations in the glycoprotein of viral haemorrhagic septicaemia virus that affect virulence for fish and the pH threshold for membrane fusion

• Published in: Journal of general virology Vol. 80; no. 5; pp. 1221 - 1229
• Main Authors: Gaudin, Y, de Kinkelin, P, Benmansour, A
• Format: Journal Article
• Language: English
• Published: England Soc General Microbiol 01-05-1999; Microbiology Society
• Subjects: Amino Acid Sequence; Animals; Antibodies, Monoclonal - immunology; Brackish; DNA, Viral - analysis; Fish Diseases - virology; Freshwater; Hydrogen-Ion Concentration; Life Sciences; Marine; Membrane Fusion; Microbiology and Parasitology; Molecular Sequence Data; Mutation; Oncorhynchus mykiss - virology; Pisces; Reverse Transcriptase Polymerase Chain Reaction; Rhabdoviridae - genetics; Rhabdoviridae - pathogenicity; Rhabdoviridae Infections - veterinary; Rhabdoviridae Infections - virology; Viral Envelope Proteins - chemistry; Viral Envelope Proteins - genetics; Viral hemorrhagic septicemia virus; Virology; Virulence - genetics; PATHOGENICITE
• ISSN: 0022-1317; 1465-2099
• DOI: 10.1099/0022-1317-80-5-1221

Y Gaudin, P de Kinkelin and A Benmansour
INRA, Unite de Virologie et Immunologie Moleculaires, 78352 Jouy-en-Josas cedex, France
To study the molecular basis of virulence of viral haemorrhagic septicaemia
virus (VHSV), we used a cross-reactive neutralizing MAb to select
MAb-resistant (MAR) mutants with reduced pathogenicity for fish. From
sequence determination of the G gene of MAR mutants, attenuated laboratory
variant and avirulent field strains, we identified two distant regions of
the glycoprotein associated with virulence: region I (aa 135--161),
homologous to the putative fusion peptide of both rabies virus (RV) and
vesicular stomatitis virus (VSV), and region II (surrounding aa 431--433),
homologous to RV and VSV domains controlling the conformational changes
necessary for the fusion process to take place. Simultaneous mutations in
both regions resulted in the most attenuated phenotype and we obtained
genetic evidence that regions I and II may be structurally linked. As the
MAR mutants had mutations in or near domains involved in fusion, the fusion
properties of VHSV and its variants were analysed. This work allowed us to
postulate that the fusion domain of VHSV is probably constituted of two
distinct regions of the protein connected through a disulfide bridge
between cysteines 110 and 152. Finally, we obtained evidence suggesting
that the pH threshold for fusion is a determinant for virulence:
restriction of fusion to a more acidic pH was associated with attenuation
for the variant tr25 which had a shift of the threshold for maximal fusion
from pH 6.30 (for the parental strain) to pH 6.00; conversely, two field
strains which had maximal fusion at pH 6.60 were the most virulent.