Functional properties of the thermostable mutL from

The methyl-directed mismatch repair (MMR) mechanism has been extensively studied in vitro and in vivo, but one of the diffi-culties in determining the biological relationships between the MMR-related proteins is the tendency of MutL to self-aggregate. The properties of a stable MutL homologue were investigated us-ing a thermostable MutL (TmL) from Thermotoga maritima MSB8 and whose size exclusion chromatographic and crosslinking analyses were compatible with a dimeric form of TmL. TmL un-derwent conformational changes in the presence of nucleotides and single-stranded DNA (ssDNA) with ATP binding not requir-ing ssDNA binding activity of TmL, while ADPnP-stimulated TmL showed a high ssDNA binding affinity. Finally, TmL inter-acted with the T. maritima MutS (TmS), increasing the affinity of TmS to mismatched DNA base pairs and suggesting that the role of TmL in the formation of a mismatched DNA-TmS complex may be a pivotal observation for the study of the initial MMR system. [BMB reports 2009; 42(1): 53-58