NMR structure of the complex between the zinc finger protein NCp10 of Moloney murine leukemia virus and the single-stranded pentanucleotide d(ACGCC):Comparison with HIV-NCp7 complexes

The structure of the 56 amino acid nucleocapsid protein NCp10 of retrovirus MoMuLV, which contains a single CX2CX4HX4C-type zinc finger, has been dete rmined previously by NMR. The important role of NCp10 (or NCp7 for HIV-1) i n the retroviral life cycle seems mainly related to their preferential bind ing to single-stranded nucleic acids. We report here the structure of the c omplex formed between the biologically active (14-53)NCp10 and the oligonuc leotide d(ACGCC) in aqueous solution determined by 2D H-1 NMR based methods . The aromatic residue Trp(35) of NCp10 directs nucleic acid complexation a s shown by its complete fluorescence quenching upon addition of d(ACGCC). H -1 and P-31 NMR studies support the insertion of Trp35 between The G(3) and C-4 bases. A total of 577 NOE distance restraints, of which 40 were interm olecular, were used for the structure determination. The zinc finger provid es a well-defined surface for the binding of d(ACGCC) through hydrophobic i nteractions and tryptophan stacking on the guanine. This latter interaction was also observed in the NMR-derived structures of the complexes between N Cp7, which contains two successive zinc fingers, and single-stranded DNA an d RNA, supporting the proposal for a major role played by aromatic residues of NCp proteins in nucleic acid recognition. Upon binding to the nucleotid e a new loop in NCp10 that participates in the intermolecular interaction i s formed. Additional interactions provided by positively charged residues s urrounding the zinc finger appear necessary for tight binding. The structur e of the complex NCp10-d(ACGCC) gives a structural explanation for the loss of virus infectivity following point mutations in the finger domain.