The role of mismatched nucleotides in activating the hMSH2-hMSH6 MolecularSwitch

Citation
S. Gradia et al., The role of mismatched nucleotides in activating the hMSH2-hMSH6 MolecularSwitch, J BIOL CHEM, 275(6), 2000, pp. 3922-3930
Citations number
40
Categorie Soggetti
Biochemistry & Biophysics
Journal title
JOURNAL OF BIOLOGICAL CHEMISTRY
ISSN journal
00219258 → ACNP
Volume
275
Issue
6
Year of publication
2000
Pages
3922 - 3930
Database
ISI
SICI code
0021-9258(20000211)275:6<3922:TROMNI>2.0.ZU;2-D
Abstract
We have previously shown that hMSH2-hMSH6 contains an intrinsic ATPase whic h is activated by mismatch-provoked ADP-->ATP exchange that coordinately in duces the formation of a sliding clamp capable of hydrolysis-independent di ffusion along the DNA backbone (1, 2), These studies suggested that mismatc h repair could be propagated by a signaling event transduced via diffusion of ATP-bound hMSH2-hMSH6 molecular switches to the DNA repair machinery. Th e Molecular Switch model (Fishel, R, (1998) Genes Dev, 12, 2096-2101) is co nsiderably different than the Hydrolysis-Driven Translocation model (Blackw ell, L. J., Martik, D., Bjornson, K. P., Bjornson, E. S., and Modrich, P. ( 1998) J. Biol, Chem. 273, 32055-32062) and makes additional testable predic tions beyond the demonstration of hydrolysis-independent diffusion (Gradia, S., Subramanian, D., Wilson, T., Acharya, S., Makhov, A., Griffith, J., an d Fishel, R, (1999) Mel. Cell 3, 255-261): (i) individual mismatch-provoked ADP-->ATP exchange should be unique and rate-limiting, and (ii) the k(cat. DNA) for the DNA-stimulated ATPase activity should decrease with increasing chain length. Here we have examined hMSH2-hMSH6 affinity and ATPase stimul atory activity for several DNA substrates containing mispaired nucleotides as well as the chain length dependence of a defined mismatch under physiolo gical conditions. We find that the results are most consistent with the pre dictions of the Molecular Switch model.