Cloning, purification and preliminary crystallographic analysis of the Bacillus subtilis GTPase YphC-GDP complex

The universally conserved prokaryotic GTPases

Members of the large superclass of P-loop GTPases share a core domain with a conserved three-dimensional structure. In eukaryotes, these proteins are implicated in various crucial cellular processes, including translation, membrane trafficking, cell cycle progression, and membrane signaling. As targets of mutation and toxins, GTPases are involved in the pathogenesis of cancer and infectious diseases. In prokaryotes also, it is hard to overestimate the importance of GTPases in cell physiology. Numerous papers have shed new light on the role of bacterial GTPases in cell cycle regulation, ribosome assembly, the stress response, and other cellular processes. Moreover, bacterial GTPases have been identified as high-potential drug targets. A key paper published over 2 decades ago stated that, "It may never again be possible to capture [GTPases] in a family portrait" (H. R. Bourne, D. A. Sanders, and F. McCormick, Nature 348:125-132, 1990) and indeed, the last 20 years have seen a tremendous increase in publications on the subject. Sequence analysis identified 13 bacterial GTPases that are conserved in at least 75% of all bacterial species. We here provide an overview of these 13 protein subfamilies, covering their cellular functions as well as cellular localization and expression levels, three-dimensional structures, biochemical properties, and gene organization. Conserved roles in eukaryotic homologs will be discussed as well. A comprehensive overview summarizing current knowledge on prokaryotic GTPases will aid in further elucidating the function of these important proteins.

The Rv1712 Locus from Mycobacterium tuberculosis H37Rv codes for a functional CMP kinase that preferentially phosphorylates dCMP

The Mycobacterium tuberculosis cmk gene, predicted to encode a CMP kinase (CMK), was cloned and expressed, and its product was purified to homogeneity. Steady-state kinetics confirmed that M. tuberculosis CMK is a monomer that preferentially phosphorylates CMP and dCMP by a sequential mechanism. A plausible role for CMK is discussed.

The essential GTPase YphC displays a major domain rearrangement associated with nucleotide binding

The structure of a Bacillus subtilis YphC/GDP complex shows that it contains two GTPase domains that pack against a central domain whose fold resembles that of an RNA binding KH-domain. Comparisons of this structure to that of a homologue in Thermotoga maritima reveals a dramatic rearrangement in the position of the N-terminal GTPase domain with a shift of up to 60 A and the formation of a totally different interface to the central domain. This rearrangement appears to be triggered by conformational changes of the switch II region in this domain in response to nucleotide binding. Modeling studies suggest that this motion represents transitions between the "on" and "off" states of the GTPase, the effect of which is to alternately expose and bury a positively charged face of the central domain that we suggest is involved in RNA recognition as part of the possible role of this enzyme in ribosome binding.