Molecular Biophysics Unit, Indian Institute of Science
A major thrust of the mycobacterial structural genomics programme in this laboratory is on recombination and repair. Central to homologous recombination is the RecA protein. The structures of several crystals of RecA from M. tuberculosis and M. smegmatis and their nucleotide complexes, have been determined (Nucleic Acids Res. 28, 4964-4973, 2000; Proteins: Structure, Function, Genet. 50, 474-485, 2003; J. Bacteriol. 185, 4280-4284, 2003). They provided the first detailed description of RecA-nucleotide interactions and the DNA binding loops in RecA, and brought to light a mechanism for transmitting information on nucleotide binding to the DNA binding region, using a crucially located glutamine residue as a trigger. More recently, the first visualisation of the usually disordered C-terminal stretch has been achieved (Nucleic Acids Res. 34, 2186-2195, 2006). This ordering is accompanied by the generation of a second nucleotide binding site, which communicates with the first in an adjacent molecule, suggesting a new route to allosteric regulation. Single stranded DNA-binding protein (SSB) also plays crucial roles in recombination and repair. Mycobacterial SSB has a novel quaternary structure with a unique dimeric interface which lends it greater stability (J. Mol. Biol. 331, 385-393, 2003; Acta Cryst. D61, 1140-1148, 2005). Also, the length of DNA necessary to wrap around the tetrameric molecule is lower in the mycobacterial proteins than in E.coli and human SSBs. The other relevant proteins currently being investigated include RuvA and uracil DNA glycosylase from M. tuberculosis.