Document 0201
 DOCN  M9550201
 TI    Human immunodeficiency virus-1 reverse transcriptase heterodimer
       stability.
 DT    9505
 AU    Lebowitz J; Kar S; Braswell E; McPherson S; Richard DL; Department of
       Microbiology, University of Alabama at Birmingham; 35294.
 SO    Protein Sci. 1994 Sep;3(9):1374-82. Unique Identifier : AIDSLINE
       MED/95135290
 AB    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.
 DE    Cold  Enzyme Stability  Heat  HIV-1/*ENZYMOLOGY  Molecular Weight
       Osmolar Concentration  Protein Conformation  Reverse
       Transcriptase/*CHEMISTRY/DRUG EFFECTS  Sodium Chloride/PHARMACOLOGY
       Support, Non-U.S. Gov't  Support, U.S. Gov't, Non-P.H.S.  Support, U.S.
       Gov't, P.H.S.  Ultracentrifugation  JOURNAL ARTICLE

       SOURCE: National Library of Medicine.  NOTICE: This material may be
       protected by Copyright Law (Title 17, U.S.Code).