Mechanism of HIV reverse transcriptase: enzyme-primer interaction as revealed through studies of a dNTP analog, 3'-azido-dTTP

• Published in: Biochemistry (Easton) 1990-04, Vol.29 (15), p.3603-3611
• Main Authors: Kedar, Padmini S, Abbotts, John, Kovacs, Terez, Lesiak, Krystyna, Torrence, Paul, Wilson, Samuel H
• Format: Article
• Language: English
• Subjects: AIDS/HIV; Analytical, structural and metabolic biochemistry; Antiviral Agents; Bacteriophages - genetics; Biological and medical sciences; Chemical Phenomena; Chemistry; Dideoxynucleotides; DNA - biosynthesis; DNA-Directed DNA Polymerase - genetics; DNA-Directed DNA Polymerase - metabolism; Enzymes and enzyme inhibitors; Fundamental and applied biological sciences. Psychology; HIV - enzymology; Kinetics; Models, Molecular; RNA-Directed DNA Polymerase - genetics; RNA-Directed DNA Polymerase - metabolism; Templates, Genetic; Thymine Nucleotides - metabolism; Transferases; Zidovudine - analogs & derivatives; Zidovudine - metabolism
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi00467a003

Primer and dNTP recognition by purified HIV reverse transcriptase have been investigated. Earlier kinetic studies suggested that the reaction pathway for DNA synthesis is ordered, with template-primer and free enzyme combining to form the first complex in the reaction sequence [Majumdar et al. (1988) J. Biol. Chem. 263, 15657-15665], and through use of a particularly high affinity template-primer analogue [r(I)n.Sd(C)28], rate values for formation of the first complex were calculated [Majumdar et al. (1989) Biochemistry 28, 1340-1346]. We now report rate values for first complex formation in the usual model replication system with poly[r(A)].oligo [d(T)] as template-primer. We find that 3'-azido-dTTP (AZTTP) is a linear competitive inhibitor of DNA synthesis against the substrate dNTP (dTTP) in the poly[r(A)].oligo[d(T)] replication system. This suggests that 3'-azido-dTTP and dTTP combine with the same form of the enzyme in the reaction scheme, i.e., the enzyme-primer complex. This is not trivial, since a second analogue, 3'-amino-dTTP, also is an inhibitor against dTTP, but the mechanism in this case is linear noncompetitive. Because the inhibition by 3'-azido-dTTP is linear competitive, the KD for physical binding to the enzyme is assumed to be the same as the Ki for inhibition (20 nM). Substrate kinetic studies of DNA synthesis using 3'-azido-dTTP as substrate revealed that the Michaelis constant is 3 microM. Therefore, the Km for this substrate analogue is 100-fold higher than the KD for binding of the analogue to the enzyme-primer complex.