Human T-lymphotrophic virus type I nucleocapsid protein NCp15: structural study and stability of the N-terminal zinc-finger

An 18-residue peptide, corresponding to the minimum sequence of the N-termi nal zinc-finger domain in the nucleocapsid of human T-lymphotrophic virus t ype I, was synthesized by a solid-phase method and fully characterized. Its ability to complex metal ions (Co2+ and Zn2+) was clearly established by U V-visible spectroscopy and MS. The stability of these complexes was investi gated by an original method with HPLC chromatography. Our results show that , even in the presence of air, the Zn2+ complex is highly stable. In contra st, the Co2+ complex undergoes a relatively fast degradation due to an intr amolecular oxidation leading to the formation of a disulphide bridge betwee n two cysteine residues. The H-1-NMR analysis indicates that Zn2+ binds to the N delta atom of the histidine residue rather than to the NE atom. Two-d imensional NMR techniques were used to determine the solution structure of the zinc-finger, illustrated by the existence of turns in the overall confo rmation.