The Biochemical journal 2017 08 15() pii 10.1042/BCJ20170480
Recent structural characterizations of the p51 and p66 monomers has established an important starting point for understanding the maturation pathway of the HIV-1 reverse transcriptase p66/p51 heterodimer. This process requires a metamorphic transition of the polymerase domain leading to formation of a p66/p66′ homodimer that exists as a structural heterodimer. In order to better understand the drivers for this metamorphic transition, we have performed NMR studies of (15)N-labeled RT216 – a construct that includes the fingers and most of the palm domains. These studies are consistent with the conclusion that the p66 monomer exists as a spring-loaded complex. Initial dissociation of the fingers/palm:connection complex allows the fingers/palm to adopt an alternate, more stable structure, reducing the rate of re-association and facilitating subsequent maturation steps. One of the drivers for an initial extension of the fingers/palm domains is identified as a straightening of helix E relative to its conformation in the monomer by eliminating a bend of ~ 50° near residue Phe160. NMR and CD data also are consistent with the conclusion that a hydrophobic surface of palm domain that becomes exposed after the initial dissociation, as well as the intrinsic conformational preferences of the palm domain C-terminal segment, facilitate formation of the b-sheet structure that is unique to the active polymerase subunit. Spectral comparisons based on (15)N-labeled constructs are all consistent with previous structural conclusions based on studies of (13)C-methyl-labeled constructs.