Strains of IBV can also be classified based on genetic characteristics of the spike glycoprotein gene, which for the most part correlates with serotype.
Four structural viral proteins designated S, M, E and N have been recognized.
Diagrammatic representation of proteins in the Infectious Bronchitis virus particle.
Model for the membrane associated peplomer or spike protein of IBV. The spike glycoprotein is made up of S1 and S2 subunits. (D. Cavanagh, 1983).