The C-terminal region of Escherichia coli MutS and protein oligomerization.

Escherichia coli MutS, an 853 amino acids oligomeric protein, is involved in the postreplicative DNA mismatch repair and avoidance of homeologous recombination. By constructing MutS mutated versions of the C-terminal region, we determined that deletion of the last 7 C-terminal amino acids is enough to abolish tetramer formation and that the K850A substitution destabilize the tetramer structure. It is proposed that the C-terminal extreme alpha helix (residues 839-850) of the protein may play an important role in protein oligomerization. We also show that the C-terminal region or the C-terminal plus the HTH domain of MutS, fused to the monomeric Maltose Binding Protein promote oligomerization of the chimeric protein. However, chemical cross-linking experiments indicate that the HTH domain improves the oligomerization properties of the fused protein. Escherichia coli cells expressing the fused proteins become hypermutator suggesting that the C-terminal region of MutS plays an important role in vivo.