Disruption of the helix-u-turn-helix motif of MutS protein: loss of subunit dimerization, mismatch binding and ATP hydrolysis.
The DNA mismatch repair protein, MutS, is a dimeric protein that recognizes mismatched bases and has an intrinsic ATPase activity. Here, a series of Taq MutS proteins having C-terminal truncations in the vicinity of a highly conserved helix-u-turn-helix (HuH) motif are assessed for subunit oligomerization, ATPase activity and DNA mismatch binding. Those proteins containing an intact HuH region are dimers; those without the HuH region are predominantly monomers in solution. Steady-state kinetics of truncated but dimeric MutS proteins reveals only modest decreases in their ATPase activity compared to full-length protein. In contrast, disruption of the HuH region results in a greatly attenuated ATPase activity. In addition, only dimeric MutS proteins are proficient for mismatch binding. Finally, an analysis of the mismatch repair competency of truncated Escherichia coli MutS proteins in a rifampicin mutator assay confirms that the HuH region is critical for in vivo function. These findings indicate that dimerization is critical for both the ATPase and DNA mismatch binding activities of MutS, and corroborate several key features of the MutS structure recently deduced from X-ray crystallographic studies.
Biswas
I
I
Genetics and Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
Obmolova
G
G
Takahashi
M
M
Herr
A
A
Newman
M A
MA
Yang
W
W
Hsieh
P
P
D000251:Adenosine Triphosphatases; D000255:Adenosine Triphosphate / Q000378:metabolism*; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D020137:Base Pair Mismatch / Q000235:genetics*; D002850:Chromatography, Gel; D002942:Circular Dichroism; D004247:DNA / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019281:Dimerization; D004352:Drug Resistance, Microbial; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics; D029968:Escherichia coli Proteins; D005816:Genetic Complementation Test; D006868:Hydrolysis; D008958:Models, Molecular; D008969:Molecular Sequence Data; D051719:MutS DNA Mismatch-Binding Protein; D009692:Nucleic Acid Heteroduplexes / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D021122:Protein Subunits; D012293:Rifampin / Q000494:pharmacology; D017384:Sequence Deletion / Q000235:genetics*; D013696:Temperature
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D009692:Nucleic Acid Heteroduplexes; D021122:Protein Subunits; D000255:Adenosine Triphosphate; D004247:DNA; D000251:Adenosine Triphosphatases; D051719:MutS DNA Mismatch-Binding Protein; C497175:MutS protein, E coli; D012293:Rifampin