RESEARCH SUMMARY

This group works to find inhibitable targets in essential bacterial functions, namely cell growth and division, with the purpose of designing assays to identify new antimicrobials. For this goal we study first the proliferation of a Gram-negative bacteria, Escherichia coli, in which both commensal and pathogenic strains exis.

In addition we extend our research to study specific topics related to the proliferation of two pathogens, Streptococcus pneumoniae causative of serious infections and Mycobacterium tuberculosis, a widespread pathogen affecting one third of the world population. We summarise two recent studies that have been published in these two years.

In the assembly of the E. coli divisome we found that FtsN is required for the correct assembly and stability of the Escherichia coli proto-ring. The proto-ring is formed by three essential proteins, FtsZ, FtsA and ZipA. This structure is the first that assembles at midcell to initiate the division ring that once completed integrates into the divisome and effects cell division. FtsN, which is considered the last division protein to be recruited into the divisome, is required for proto-ring stability in the living cell. In its absence, the already formed rings of FtsQ, FtsA, ZipA and even FtsZ disassemble. The ZipA presence in the proto-ring is the most sensitive to the decrease in the levels of FtsN.

In collaboration with P. Gómez-Puertas (CBMSO) we have studied the need for potassium and neutral pH to attain the optimum GTPase activity and polymerisation of FtsZ, the prokaryotic ortholog of Tubulin. We used molecular dynamics simulations of the Methanococcus janaschii FtsZ dimer in the presence of GTP-magnesium and monovalent cations. The presence of potassium at the GTP binding site allows the positioning of one water molecule favouring dimer stability and GTP hydrolysis. Sodium destabilizes the dimer and does not allow the positioning of the water. Simulating low pH by protonation of the gamma phosphate of GTP indicated that both the monovalent cation and the water molecule should be excluded from the binding site.

The simulation therefore predicted that at low pH the FtsZ GTP-ase activity should be lower and the dimer more stable. These predictions were tested and proven correct experimentally by analyzing the GTPase and polymerization activities of M. jannaschii and E. coli FtsZ proteins in the test tube.