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M9550201.TXT
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1995-03-04
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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).