Rotavirus YM gene 4: analysis of its deduced amino acid sequence and prediction of the secondary structure of the VP4 protein

We have determined the complete nucleotide sequence of the VP4 gene of porcine rotavirus YM. It is 2,362 nucleotides long, with a single open reading frame coding for a protein of 776 amino acids. A phylogenetic tree was derived from the deduced YM VP4 amino acid sequence and 18 other available VP4 sequences of rotavirus strains belonging to different serotypes and isolated from different animal species. In this tree, VP4 proteins were grouped by the hosts that the corresponding viruses infect rather than by the serotypes they belong to, suggesting that this protein is involved in the host specificity of the viruses. In an attempt to predict the secondary structure of the VP4 protein, we selected the more divergent VP4 sequences and made a secondary structure analysis of each protein. In spite of variations within the individual structures predicted, there was a general structural pattern which suggested the existence of at least two different domains. One, comprising the amino-terminal 63% of the protein, is predicted to be a possible globular domain rich in beta-strands alternated with turns and coils. The second domain, represented by the remaining, carboxy-terminal part of VP4, is rich in long stretches of alpha-helix, one of which, 63 amino acids long, has heptad repeats resembling those found in proteins known to form alpha-helical coiled-coils. The predicted secondary structure correlates well with the available data on the protein accessibility delineated by immunological and biochemical findings and with the spike structure of the protein, which has been determined by cryoelectron microscopy