Mismatch repair (MMR) in E. coli is initiated by three proteins, MutS, MutL and MutH to specifically target newly synthesized daughter strand. MutS is an ATPase and recognizes a mismatched base-pair as well as an insertion or deletion of 1-4 nucleotides in one strand. MutH is a latent endonuclease that is both sequence- and methylation-specific; when activated by MutS upon detection of a mismatch, it cleaves 5 to the unmethylated d(GATC) sequence in a hemimethylated duplex. MutL is also an ATPase and mediates the communication between MutS and MutH, which do not directly interact. Once a nick is introduced to the daughter strand by MutH, UvrD helicase, single-strand binding protein and DNA exonuclease are recruited by MutS and MutL to remove nucleotides from the nick to beyond the mismatch. Homologues of MutS and MutL are found in all eukaryotes, and malfunction of either human MutS or MutL homolog is directly implicated in the susceptibility to hereditary non-polyposis colorectal cancer (HNPCC) and other sporadic cancers. Our previous studies led to the determination of crystal structures of MutS, MutS-mismatch DNA and MutS-mismatch-ADP complexes, the N- and C-terminal domain of MutL, and finally MutH and MutH-DNA complexes. We also characterized the role of the MutS and MutL ATPases and the cleavage specificity of MutH. In this fiscal year, we have succeeded in determining a series of crystal structures of UvrD helicase-DNA complexes, which represent consecutive physical steps of UvrD unwinding a duplex DNA in an ATP hydrolysis cycle. In addition, we have carried out mutagenesis studies to dissect two alternative mechanisms of DNA unwinding by UvrD. Our manuscript UvrD helicase unwinds DNA one base pair at a time by a two-part power stroke was published in Cell in December 2006. Currently we are engaging in (1) obtaining large protein-DNA assemblies, e.g. MutL-DNA, MutL-UvrD-DNA, MutS-MutL-DNA complexes, for structural characterization, (2) pre-steady state kinetic studies of the ATPases involved in mismatch repair, and (3) expanding structural and mechanistic studies to eukaryotic mismatch repair systems. In the previous year (2010-2011), we published our structural analysis of human MutSbeta-DNA complex in NSMB. Dr. Ning Li has spent last three years probing the human and bacterial mismatch repair using protein-DNA crosslinking technique and made macromolecular complexes for structural analysis. References Gu, H. Z., Yang, W. & Seeman, N. C. (2010). DNA scissors device used to measure MutS binding to DNA mis-pairs, JACS, 132, p4252-4357. Yang, W. (2010) Lessons learnt from UvrD helicase: mechanism for directional movement. Ann. Rev. Biophys., 39, 367-385.

Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Zip Code
Cheng, Xiaoming; Xia, Yuchen; Serti, Elisavet et al. (2017) Hepatitis B virus evades innate immunity of hepatocytes but activates cytokine production by macrophages. Hepatology 66:1779-1793
Zhao, Xiao-Nan; Kumari, Daman; Gupta, Shikha et al. (2015) Muts? generates both expansions and contractions in a mouse model of the Fragile X-associated disorders. Hum Mol Genet 24:7087-96
Li, Feng; Mao, Guogen; Tong, Dan et al. (2013) The histone mark H3K36me3 regulates human DNA mismatch repair through its interaction with MutS?. Cell 153:590-600
Gupta, Shikha; Gellert, Martin; Yang, Wei (2011) Mechanism of mismatch recognition revealed by human MutS? bound to unpaired DNA loops. Nat Struct Mol Biol 19:72-8
Yang, Wei (2011) Nucleases: diversity of structure, function and mechanism. Q Rev Biophys 44:1-93
Gu, Hongzhou; Yang, Wei; Seeman, Nadrian C (2010) DNA scissors device used to measure MutS binding to DNA mis-pairs. J Am Chem Soc 132:4352-7
Yang, Wei (2010) Lessons learned from UvrD helicase: mechanism for directional movement. Annu Rev Biophys 39:367-85
Biertümpfel, Christian; Zhao, Ye; Kondo, Yuji et al. (2010) Structure and mechanism of human DNA polymerase eta. Nature 465:1044-8