DNA-dependent activation of the hMutSalpha ATPase.
ATP hydrolysis by MutS homologs is required for function of these proteins in mismatch repair. However, the function of ATP hydrolysis in the repair reaction is controversial. In this paper we describe a steady-state kinetic analysis of the DNA-activated ATPase of human MutSalpha. Comparison of salt concentration effects on mismatch repair and mismatch-provoked excision in HeLa nuclear extracts with salt effects on the DNA-activated ATPase suggests that ATP hydrolysis by MutSalpha is involved in the rate determining step in the repair pathway. While the ATPase is activated by homoduplex and heteroduplex DNA, the half-maximal concentration for activation by heteroduplex DNA is significantly lower under physiological salt concentrations. Furthermore, at optimal salt concentration, heteroduplex DNA increases the kcat for ATP hydrolysis to a greater extent than does homoduplex DNA. We also demonstrate that the degree of ATPase activation is dependent on DNA chain length, with the kcat for hydrolysis increasing significantly with chain length of the DNA cofactor. These results are discussed in terms of the translocation (Allen, D. J., Makhov, A., Grilley, M., Taylor, J., Thresher, R., Modrich, P., and Griffith, J. D. (1997) EMBO J. 16, 4467-4476) and the molecular switch (Gradia, S., Acharya, S., and Fishel, R. (1997) Cell 91, 995-1005) models that invoke distinct roles for ATP hydrolysis in MutS homolog function.
Blackwell
L J
LJ
Howard Hughes Medical Institute, Duke University Medical Center, Durham, North Carolina 27710, USA.
Bjornson
K P
KP
Modrich
P
P
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D020137:Base Pair Mismatch; D001483:Base Sequence; D002467:Cell Nucleus / Q000378:metabolism; D004247:DNA / Q000378:metabolism*; D004260:DNA Repair / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004706:Endodeoxyribonucleases / Q000378:metabolism*; D004789:Enzyme Activation; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D009097:Multienzyme Complexes / Q000378:metabolism*; D000074081:MutS Homolog 3 Protein; D009692:Nucleic Acid Heteroduplexes / Q000378:metabolism; D009838:Oligodeoxyribonucleotides / Q000737:chemistry / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology; D013379:Substrate Specificity
D000251:Adenosine Triphosphatases; D004247:DNA; D004268:DNA-Binding Proteins; D004706:Endodeoxyribonucleases; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D009097:Multienzyme Complexes; D000074081:MutS Homolog 3 Protein; D009692:Nucleic Acid Heteroduplexes; D009838:Oligodeoxyribonucleotides; D011189:Potassium Chloride; C078444:MSH3 protein, human; C036400:DNA-dependent ATPase-endonuclease; C421109:multidrug resistance-associated protein 1