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The dTTPase Mechanism of T7 DNA Helicase Resembles the Binding Change Mechanism of the F1-ATPase
Manju M. Hingorani, M. Todd Washington, Kristen C. Moore and Smita S. Patel
Proceedings of the National Academy of Sciences of the United States of America
Vol. 94, No. 10 (May 13, 1997), pp. 5012-5017
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/42440
Page Count: 6
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Bacteriophage T7 DNA helicase is a ring-shaped hexamer that catalyzes duplex DNA unwinding using dTTP hydrolysis as an energy source. Of the six potential nucleotide binding sites on the hexamer, we have found that three are noncatalytic sites and three are catalytic sites. The noncatalytic sites bind nucleotides with a high affinity, but dTTPs bound to these sites do not dissociate or hydrolyze through many dTTPase turnovers at the catalytic sites. The catalytic sites show strong cooperativity which leads to sequential binding and hydrolysis of dTTP. The elucidated dTTPase mechanism of the catalytic sites of T7 helicase is remarkably similar to the binding change mechanism of the ATP synthase. Based on the similarity, a general mechanism for hexameric helicases is proposed. In this mechanism, an F1-ATPase-like rotational movement around the single-stranded DNA, which is bound through the central hole of the hexamer, is proposed to lead to unidirectional translocation along single-stranded DNA and duplex DNA unwinding.
Proceedings of the National Academy of Sciences of the United States of America © 1997 National Academy of Sciences