6a2t
Mycobacterium tuberculosis LexA C-domain K197A
Structural highlights
FunctionLEXA_MYCTU Represses a number of genes involved in the response to DNA damage (SOS response), including recA and lexA. Has been shown to bind to the 14 bp palindromic sequence 5'-CGAACNNNNGTTCG-3'. In the presence of single-stranded DNA, RecA interacts with LexA causing an autocatalytic cleavage which disrupts the DNA-binding part of LexA, leading to derepression of the SOS regulon and eventually DNA repair. Publication Abstract from PubMedLexA is a protein that is involved in the SOS response. The protein from Mycobacterium tuberculosis and its mutants have been biochemically characterized and the structures of their catalytic segments have been determined. The protein is made up of an N-terminal segment, which includes the DNA-binding domain, and a C-terminal segment encompassing much of the catalytic domain. The two segments are defined by a cleavage site. Full-length LexA, the two segments, two point mutants involving changes in the active-site residues (S160A and K197A) and another mutant involving a change at the cleavage site (G126D) were cloned and purified. The wild-type protein autocleaves at basic pH, while the mutants do not. The wild-type and the mutant proteins dimerize and bind DNA with equal facility. The C-terminal segment also dimerizes, and it also shows a tendency to form tetramers. The C-terminal segment readily crystallized. The crystals obtained from attempts involving the full-length protein and its mutants contained only the C-terminal segment including the catalytic core and a few residues preceding it, in a dimeric or tetrameric form, indicating protein cleavage during the long period involved in crystal formation. Modes of tetramerization of the full-length protein similar to those observed for the catalytic core are feasible. A complex of M. tuberculosis LexA and the cognate SOS box could be modeled in which the mutual orientation of the two N-terminal domains differs from that in the Escherichia coli LexA-DNA complex. These results represent the first thorough characterization of M. tuberculosis LexA and provide definitive information on its structure and assembly. They also provide leads for further exploration of this important protein. Biochemical characterization of Mycobacterium tuberculosis LexA and structural studies of its C-terminal segment.,Chandran AV, Srikalaivani R, Paul A, Vijayan M Acta Crystallogr D Struct Biol. 2019 Jan 1;75(Pt 1):41-55. doi:, 10.1107/S2059798318016066. Epub 2019 Jan 7. PMID:30644844[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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