Agnoprotein of mammalian polyomaviruses

Abstract

Polyomaviruses are naked viruses with an icosahedral capsid that surrounds a circular double-stranded DNA molecule of about 5000 base-pairs. Their genome encodes at least five proteins: large and small tumor antigens and the capsid proteins VP1, VP2 and VP3. The tumor antigens are expressed during early stages of the viral life cycle and are implicated in the regulation of viral transcription and DNA replication, while the capsid proteins are produced later during infection. Members of the Polyomaviridae family have been isolated in birds (Avipolyomavirus) and mammals (Orthopolyomavirus and Wukipolyomavirus). Some mammalian polyomaviruses encode an additional protein, referred to as agnoprotein, which is a relatively small polypeptide that exerts multiple functions. This review discusses the structure, post-translational modifications, and functions of agnoprotein, and speculates why not all polyomaviruses express this protein.

Fig. 1

Alignment of the amino acid sequences of the agnoprotein from different polyomaviruses. The single letter amino acid code is used. Red represents small and hydrophobic amino acids (A, F, I, L, M, P, V, W), blue symbolizes acidic amino acids (D, E), magenta corresponds to basic amino acids (K, R), and green stands for hydroxyl, amine and basic amino acids (C, G, H, N, Q, S, T, Y). An asterisk indicates an identical amino acid. The domain required for oligomerization is shaded in yellow. Putative ubiquitination sites are underlined (Tung and Ho, 2008; Lee et al., 2011). The Clustal series of programs were used for multiple alignments (Chenna et al., 2003).