PMID:10715140
| Citation |
Bjornson, KP, Allen, DJ and Modrich, P (2000) Modulation of MutS ATP hydrolysis by DNA cofactors. Biochemistry 39:3176-83 |
|---|---|
| Abstract |
Escherichia coli MutS protein, which is required for mismatch repair, has a slow ATPase activity that obeys Michalelis-Menten kinetics. At 37 degrees C, the steady-state turnover rate for ATP hydrolysis is 1.0 +/- 0.3 min(-1) per monomer equivalent with a K(m) of 33 +/- 6 microM. Hydrolysis is competitively inhibited by the ATP analogues AMPPNP and ATPgammaS, with K(i) values of 4 microM in both cases, and by ADP with a K(i) of 40 microM. The rate of ATP hydrolysis is stimulated 2-5-fold by short hetero- and homoduplex DNAs. The concentration of DNA cofactor that yields half-maximal stimulation is lowest for oligodeoxynucleotide duplexes that contain a mismatched base pair. Pre-steady-state chemical quench analysis has demonstrated a substoichiometric initial burst of ADP formation by free MutS that is governed by a rate constant of 78 min(-1), indicating that the rate-limiting step for the steady-state reaction occurs after hydrolysis. Prebinding of MutS to homoduplex DNA does not alter the burst kinetics or amplitude but only increases the steady-state rate. In contrast, binding of the protein to heteroduplex DNA abolishes the burst of ADP formation, indicating that the rate-limiting step now occurs before hydrolysis. Gel filtration analysis indicates that the MutS dimer assembles into higher order oligomers in a concentration-dependent manner, and that ATP binding shifts this equilibrium to favor assembly. These results, together with kinetic findings, indicate nonequivalence of subunits within a MutS oligomer with respect to ATP hydrolysis and DNA binding. |
| Links | |
| Keywords |
Adenosine Triphosphatases/chemistry; Adenosine Triphosphatases/metabolism; Adenosine Triphosphate/chemistry; Adenosine Triphosphate/metabolism; Bacterial Proteins/chemistry; Bacterial Proteins/genetics; Bacterial Proteins/metabolism; Base Pair Mismatch; DNA Repair; DNA, Bacterial/chemistry; DNA, Bacterial/metabolism; DNA-Binding Proteins; Dimerization; Escherichia coli/enzymology; Escherichia coli/genetics; Escherichia coli Proteins; Hydrolysis; Kinetics; MutS DNA Mismatch-Binding Protein; Nucleic Acid Heteroduplexes/chemistry |
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