Formation of transient dimers by a retroviral protease

Overview & Synopsis

Retroviral proteases have been shown previously to be only active as homodimers. They are essential to form the separate and active proteins from the viral precursors. Spumaretroviruses produce separate precursors for Gag and Pol, rather than a Gag and a Gag-Pol precursor. Nevertheless, processing of Pol into a protease-reverse transcriptase (PR-RT) and integrase is essential in order to obtain infectious viral particles. We showed recently that the PR-RT from a simian foamy virus as well as the separate protease domain (PRshort) exhibit proteolytic activities, although only monomeric forms could be detected. Here, we demonstrate that PRshort and PR-RT can be inhibited by the putative dimerization inhibitor cholic acid. Various other inhibitors, including darunavir and tipranavir, known to prevent HIV-1 PR dimerization in cells, had no effect on foamy virus protease in vitro. 1H-15N HSQC NMR analysis of PRshort indicates that cholic acid binds in the proposed dimerization interface of PRshort and appears to impair formation of the correct dimer. NMR analysis by paramagnetic relaxation enhancement resulted in elevated transverse relaxation rates of those amino acids predicted to participate in dimer formation. Our data suggest the formation of transient PRshort homodimers under native conditions that are only present as a minor transient species not detectable by traditional methods.