MutL is required to assist the mismatch repair protein MutS during initiation of 
the methyl-directed mismatch repair (MMR) response in various organisms ranging 
from prokaryotes to eukaryotes. Despite this necessity, the inherent propensity 
of MutL to aggregate has led to significant difficulties in determining its 
biological relationship with other MMR-related proteins. Here, we perform 
analysis on the thermostable MutL protein found in Thermotoga maritima MSB8 
(TmL). Size exclusion chromatographic analysis indicates the lack of aggregated 
forms with the exception of a dimeric TmL. Small-angle X-ray scattering (SAXS) 
analysis reveals that the solution structures of the full-length TmL and its 
corresponding complexes with nucleotides and ssDNA undergo conformational 
changes. The elucidated TmL SAXS model is superimposed to the crystal structure 
of the C-terminal domain of Escherichia coli MutL. In addition, the N-terminal 
SAXS model of TmL exists as monomeric form, indicating that TmL has a 
structurally flexible N-terminal domain. TmL SAXS analysis can suggest a 
considerable possibility on a new 3D view of the previously unresolved 
full-length MutL molecule.