Biochemical and Structural studies on SofG, a GTPase involved in motility of Myxococcus xanthus

Abstract

Motility in bacteria is a fundamental process. Molecular mechanism behind novel modes of bacterial motility such as social motility and adventurous gliding motility in the social bacterium, Myxococcus xanthus, has not been fully elucidated. Recent studies in motility of Myxococcus xanthus showed the use of GTPases in deciding the polarity of the bacteria which leads to change in direction during movement. SofG is expected to be a GTPase that helps in polar localisation of PilB and PilT and thus help in pili formation. Towards understanding the mechanism of action of SofG, in vitro studies on Myxococcus xanthus SofG were carried out by cloning, optimising the protein purification protocol and thus purifying the protein from heterologous expression in E. coli. The oligomeric status of the purified SofG is a homogenous monomer, as observed from size exclusion chromatography. Circular dichroism spectroscopy showed that the purified protein exhibits secondary structure and also folded well. GTPase activity assays demonstrated that SofG is indeed a GTPase as it hydrolysed GTP. Structural studies have been initiated with setting up of crystallisation trials of the homogeneous protein sample. This could lead to crystallisation of the protein and determination of its crystal structure. These biochemical, biophysical and structural characterisation of SofG will contribute towards understanding the molecular mechanism of Myxococcus motility.