Arch Virol (1997) 142: 2249±2256
Identi®cation of amino acids involved in a serotype
and neutralization speci®c epitope within the s1 subunit
of avian infectious bronchitis virus
K. M. Moore, M. W. Jackwood, and D. A. Hilt
Department of Avian Medicine, University of Georgia, Athens, Georgia, U.S.A.
Accepted June 15, 1997
Summary. Localization of neutralizing, serotype speci®c epitopes of infectious
bronchitis virus has been dif®cult because these epitopes are conformationally
dependent. We identi®ed amino acids involved in a serotype speci®c,
conformationally dependent epitope by analysis of the S1 gene of 13 mono-
clonal antibody-neutralization-resistant mutants. Substitutions in the predicted
amino acid sequence of these mutants were located at residues 304 and/or 386.
Most of the substitutions at residue 304 were from threonine to isoleucine,
whereas the substitutions at residue 386 were from arginine to proline,
histidine, cysteine, or tryptophan. Based on this data, it appears that AA
residues at 304 and 386 on the S1 glycoprotein are involved in a virus neutral-
izing serotype speci®c epitope.
Avian infectious bronchitis virus (IBV), the etiologic agent of infectious
bronchitis (IB), causes an upper respiratory tract disease in chickens. In
addition to respiratory disease, IBV may cause damage to the reproductive
tract, and some strains cause nephritis and urolithiasis. Economic losses are due
to poor weight gains in broilers, egg production losses, and decreased egg
quality in layers and breeders . Multiple IBV serotypes complicate vaccina-
tion programs due to a lack of cross protection between serotypes [6, 10, 21].
Infectious bronchitis virus, a member of the Coronaviridae family, contains
the following structural proteins ± a phosphorylated nucleocapsid protein, a
membrane glycoprotein, a small membrane protein, and a spike glycoprotein.
The spike glycoprotein is post-translationally cleaved into S1 and S2 subunits
. The S1 subunit forms a globular structure anchored to the viral membrane
by the S2 subunit . The S1 subunit is associated with virus neutralization,
hemagglutination (HA), membrane fusion, and attachment [3, 4, 15, 18, 19].