The role of MutS oligomers on Pseudomonas aeruginosa Mismatch Repair System Activity

MIGUEL V , MONTI MR, ARGARANA CE

DNA Repair

Año: 2008 vol. 7 p. 1799 - 1808

1568-7864

The Escherichia coli DNA Mismatch Repair (MMR) protein MutS exist as dimers and tetramersin solution, and the identification of its functional oligomeric state has been matter of extensivestudy. In the present work, we have analyzed the oligomerization state of MutS fromPseudomonas aeruginosa a bacterial species devoid ofDammethylation and MutH homologue.By analyzing native MutS and differentmutated versions of the protein,we determined thatP. aeruginosa MutS is mainly tetrameric in solution and that its oligomerization capacity isconducted as in E. coli, by the C-terminal region of the protein. The analysis of mismatcholigonucleotide binding activity showed that wild-type MutS binds to DNA as tetramer. TheDNA binding activity decreased when the C-terminal region was deleted (MutS798) orwhen a full-length MutS with tetramerization defects (MutSR842E) was tested. The ATPaseactivity of MutS798 was similar to MutSR842E and diminished respect to the wild-typeprotein. Experiments carried out on a P. aeruginosa mutS strain to test the proficiency ofdifferent oligomeric versions of MutS to function in vivo showed that MutS798 is not functionaland that full-length dimeric version MutSR842E, is not capable of completely restoringthe MMR activity of the mutant strain. Additional experiments carried out in conditions ofhigh mutation rate induced by the base analogue 2-AP confirm that the dimeric version ofMutS is not as efficient as the tetrameric wild-type protein to preventmutations. Therefore,it is concluded that although dimeric MutS is sufficient for MMR activity, optimal activity isobtained with the tetrameric version of the protein and therefore it should be consideredas the active form of MutS in P. aeruginosa.