Article

Altered Dynamics of DNA Bases Adjacent to a Mismatch: A Cue for Mismatch Recognition by MutS

Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India.
Journal of Molecular Biology (Impact Factor: 4.33). 12/2007; 374(1):39-53. DOI: 10.1016/j.jmb.2007.08.065
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ABSTRACT The structural deviations as well as the alteration in the dynamics of DNA at mismatch sites are considered to have a crucial role in mismatch recognition followed by its repair utilizing mismatch repair family proteins. To compare the dynamics at a mismatch and a non-mismatch site, we incorporated 2-aminopurine, a fluorescent analogue of adenine next to a G.T mismatch, a C.C mismatch, or an unpaired T, and at several other non-mismatch positions. Rotational diffusion of 2-aminopurine at these locations, monitored by time-resolved fluorescence anisotropy, showed distinct differences in the dynamics. This alteration in the motional dynamics is largely confined to the normally matched base-pairs that are immediately adjacent to a mismatch/ unpaired base and could be used by MutS as a cue for mismatch-specific recognition. Interestingly, the enhanced dynamics associated with base-pairs adjacent to a mismatch are significantly restricted upon MutS binding, perhaps "resetting" the cues for downstream events that follow MutS binding. Recognition of such details of motional dynamics of DNA for the first time in the current study enabled us to propose a model that integrates the details of mismatch recognition by MutS as revealed by the high-resolution crystal structure with that of observed base dynamics, and unveils a minimal composite read-out involving the base mismatch and its adjacent normal base-pairs.

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    • "In this model organism, the MMR pathway involves a large set of proteins and is initiated by the ternary MutS/MutL/MutH complex (Hsieh, 2001; Yang, 2000). The central part of the complex is the protein MutS, which recognizes and binds to mismatched DNA base pairs (Nag et al., 2007; Obmolova et al., 2000). MutS2, a procaryotic homolog of the widely-conserved MutS proteins, is proposed to interfere with homologous/homeologous recombination (Pinto et al., 2005). "
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    • "In this model organism, the MMR pathway involves a large set of proteins and is initiated by the ternary MutS/MutL/MutH complex (Hsieh, 2001; Yang, 2000). The central part of the complex is the protein MutS, which recognizes and binds to mismatched DNA base pairs (Nag et al., 2007; Obmolova et al., 2000). MutS2, a procaryotic homolog of the widely-conserved MutS proteins, is proposed to interfere with homologous/homeologous recombination (Pinto et al., 2005). "
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