Oligomerization of a MutS mismatch repair protein from Thermus aquaticus

The MutS DNA mismatch protein recognizes heteroduplex DNAs containing mispa ired or unpaired bases. We have examined the oligomerization of a MutS prot ein from Thermus aquaticus that binds to heteroduplex DNAs at elevated temp eratures. Analytical gel filtration, cross-linking of MutS protein with dis uccinimidyl suberate, light scattering, and matrix-assisted laser desorptio n/ionization time-of-flight mass spectrometry establish that the Tag protei n is largely a dimer in free solution, Analytical equilibrium sedimentation showed that the oligomerization of Tag MutS involves a dimer-tetramer equi librium in which dimer predominates at concentrations below 10 mu M. The De lta G(2-4)(0) for the dimer to tetramer transition is approximately -6.9 +/ - 0.1 kcal/mol of tetramer, Analytical gel filtration of native complexes a nd gel mobility shift assays of an maltose-binding protein-MutS fusion prot ein bound to a short, 37-base pair heteroduplex DNA reveal that the protein binds to DNA as a dimer with no change in oligomerization upon DNA binding .