SHARED MOTIFS OF THE CAPSID PROTEINS OF HEPADNAVIRUSES AND RETROVIRUSES SUGGEST A COMMON EVOLUTIONARY ORIGIN

The structure of the dimeric C-terminal domain of the HIV-1 capsid pro tein (CA), recently determined by X-ray crystallography (Gamble et al, (1997)), has a notable resemblance to the structure of the hepatitis B virus (HBV) capsid protein (Cp) dimer, previously determined by cryo -electron microscopy (Conway et al, (1997), Bottcher et al, (1997)). I n both proteins, dimerization is effected by formation of a four-helix bundle, whereby each subunit contributes a helix-loop-helix and most of the interaction between subunits is mediated by one pair of helices . These are the first two observations of a motif that is common to th e capsid proteins of two enveloped viruses and quite distinct from the eight-stranded anti-parallel beta-barrel found in most other virus ca psid proteins solved to date (Harrison et al, (1996)). Motivated by th e structural resemblance, we have examined retroviral and HBV capsid p rotein sequences and found weak but significant similarities between t hem. These similarities further support an evolutionary relationship b etween these two virus families of great medical importance - the hepa dnaviruses (e,g, HBV) and retroviruses (e.g. HIV). (C) 1998 Federation of European Biochemical Societies.