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The nucleocapsid protein of Moloney murine leukemia virus (NCp10) is a 56-amino
acid protein which contains one zinc finger of the CysX2CysX4HisX4Cys form, a
highly conserved motif present in most retroviruses and retroelements. At pH
> or = 5, NCp10 binds one zinc atom and the complexation induces a folding of
the CysX2CysX4HEsX4Cys box, similar to that observed for the zinc-binding
domains of HIV-1 NC protein. The three-dimensional structure of NCp10 has been
determined in aqueous solution by 600 MHz 1H NMR spectroscopy. The proton
resonances could be almost completely assigned by means of phase-sensitive
double-quantum-filtered COSY, TOCSY and NOESY techniques. NOESY spectra yielded
597 relevant structural constraints, which were used as input for distance
geometry calculations with DIANA. Further refinement was performed by
minimization with the program AMBER, which was modified by introducing a zinc
force field. The solution structure is characterized by a well-defined central
zinc finger (rmsd of 0.747 +/- 0.209 A for backbone atoms and 1.709 +/- 0.187 A
when all atoms are considered), surrounded by flexible N- and C-terminal
domains. The Tyr28, Trp35, Lys37, Lys41 and Lys42 residues, which are essential
for activity, lie on the same face of the zinc finger, forming a bulge structure
probably involved in viral RNA binding. The significance of these structural
characteristics for the various biological functions of the protein is
discussed, taking into account the results obtained with various mutants.
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