2.2-ANGSTROM RESOLUTION STRUCTURE OF THE AMINO-TERMINAL HALF OF HIV-1REVERSE-TRANSCRIPTASE (FINGERS AND PALM SUBDOMAINS)

Background: HIV-1 reverse transcriptase (RT) catalyzes the transformat ion of single-stranded viral RNA into double-stranded DNA, which is in tegrated into host cell chromosomes. The molecule is a heterodimer of two subunits, p51 and p66. The amino acid sequence of p51 is identical to the sequence of the amino-terminal subdomains of p66. Earlier crys tallogaphic studies indicate that the RT molecule is flexible, which m ay explain the difficulty in obtaining high-resolution data for the in tact protein. We have therefore determined the structure of a fragment of RT (RT216), which contains only the amino-terminal half of the RT molecule ('finger' and 'palm' subdomains). Results: The crystal struct ure of RT216 has been refined at 2.2 Angstrom resolution to a crystall ographic R-value of 20.8%. The structure is very similar to that of th e corresponding part of the p66 subunit in the p66/p51 heterodimer, al though there is a small difference in the relative orientation of the two subdomains compared with the structure of an RT-DNA-antibody fragm ent complex. There are a large number of stabilizing contacts (mainly hydrogen bonds and hydrophobic interactions) between the subdomains. T he locations of conserved amino acids and the position of some importa nt drug-resistant mutations are described. Conclusions: The RT216 stru cture provides detailed three-dimensional information of one important part of HIV-1 RT (including the critical active site residues). We pr opose a model to explain the inhibitory effect of non-nucleoside inhib itors, which partially accounts for their effect in terms of conformat ional changes of active site residues.