Structural investigation on the requirement of CCHH zinc finger type in nucleocapsid protein of human immunodeficiency virus 1

The nucleocapsid proteins (NCps) of lentiviruses play a key role during the retroviral replication cycle. NCps contain one or two highly conserved dom ains characterized by a CX2CX4HX4C sequence which binds zinc with a high af finity. The reasons of the high conservation of zinc fingers of CCHC type i n lentiviruses were investigated by a structural study of mutants in which the zinc-coordinated ligands were exchanged. The HCHC form was unable to bi nd zinc tetrahedrally, whereas in His(28)(13-30)NCp7 corresponding to the C CHH motif, the zinc was tightly complexed. The mutant peptide exists in two interconverting conformations E and D [Delta G(DE) (293K) = 0.1 kcal/mol] arising from the zinc coordination of His(28), by either its N epsilon 2 or its N delta 1, respectively. As compared to the native CCHC zinc finger, t he Cys(28) --> His mutation induces structural changes in the finger due to a modification in the coordination state of His(23) bound to zinc by N eps ilon 2 in the wild-type finger by N delta 1 in both conformers of the mutan t, Introduction of these single mutations within the NCp7 proximal zinc fin ger in the HIV-I genome was very recently shown to result in a loss of vira l infection. This supports the hypothesis that structural changes of the zi nc finger domain of NCp7 inhibit the recognition of one or several targets critically involved in the virus life cycle.