title: Human immunodeficiency virus-1 reverse transcriptase heterodimer stability.
abstract: Structural and biochemical evidence strongly supports a heterodimeric (p66p51) active form for human immunodeficiency virus-1 reverse transcriptase (RT). Heterodimer stability was examined by sedimentation analysis as a function of temperature and ionic strength. Using NONLIN regression software, monomer-dimer-trimer and monomer-dimer-tetramer association models gave the best fit to the analytical ultracentrifuge sedimentation equilibrium data. The heterodimer is the predominant form of RT at 5 degrees C, with a dimerization Ka value of 5.2 x 10(5) M-1 for both models. Ka values of 2.1 x 10(5) and 3.8 x 10(5) M-1 were obtained for the respective association models at 20 degrees C. RT in 50 and 100 mM Tris, pH 7.0, completely dissociates at 37 degrees C and behaves as an ideal monomeric species. The dissociation of RT as a function of increasing temperature was also observed by measuring the decrease in sedimentation velocity (sw,20). If the stabilization of the heterodimer was due primarily to hydrophobic interactions we would anticipate an increase in the association from 21 degrees C to 37 degrees C. The opposite temperature dependence for the association of RT suggests that electrostatic and hydrogen bond interactions play an important role in stabilizing heterodimers. To examine the effect of ionic strength on p66p51 association we determined the changes in sw,20 as a function of NaCl concentration. There is a sharp decrease in sw,20 between 0.10 and 0.5 M NaCl, leading to apparent complete dissociation. The above results support a major role for electrostatic interactions in the stabilization of the RT heterodimer.
authors.affiliation: Department of Microbiology, University of Alabama at Birmingham 35294.
authors.forename: J
authors.initials: J
authors.lastname: Lebowitz
authors.forename: S
authors.initials: S
authors.lastname: Kar
authors.forename: E
authors.initials: E
authors.lastname: Braswell
authors.forename: S
authors.initials: S
authors.lastname: McPherson
authors.forename: D L
authors.initials: DL
authors.lastname: Richard
mesh_terms: D003080:Cold Temperature; D004795:Enzyme Stability; D054303:HIV Reverse Transcriptase; D015497:HIV-1 / Q000201:enzymology*; D006358:Hot Temperature; D008970:Molecular Weight; D009994:Osmolar Concentration; D011487:Protein Conformation; D012194:RNA-Directed DNA Polymerase / Q000737:chemistry* / Q000187:drug effects; D012965:Sodium Chloride / Q000494:pharmacology; D014461:Ultracentrifugation
chemical_list: D012965:Sodium Chloride; D054303:HIV Reverse Transcriptase; D012194:RNA-Directed DNA Polymerase