Characterization of Conserved and Novel Septal Factors in Mycobacterium smegmatis

Abstract

Septation in bacteria requires coordinated regulation of cell wall biosynthesis and hydrolysis enzymes so that new septal cross-wall can be appropriately constructed without compromising the integrity of the existing cell wall. Bacteria with different modes of growth and different types of cell wall require different regulators to mediate cell growth and division processes. Mycobacteria have both a cell wall structure and a mode of growth that are distinct from well-studied model organisms and use several different regulatory mechanisms. Here, using , we identify and characterize homologs of the conserved cell division regulators FtsL and FtsB, and show that they appear to function similarly to their homologs in We identify a number of previously undescribed septally localized factors which could be involved in cell wall regulation. One of these, SepIVA, has a DivIVA domain, is required for mycobacterial septation, and is localized to the septum and the intracellular membrane domain. We propose that SepIVA is a regulator of cell wall precursor enzymes that contribute to construction of the septal cross-wall, similar to the putative elongation function of the other mycobacterial DivIVA homolog, Wag31. The enzymes that build bacterial cell walls are essential for cell survival but can cause cell lysis if misregulated; thus, their regulators are also essential. The number and nature of these regulators is likely to vary in bacteria that grow in different ways. The mycobacteria are a genus that have a cell wall whose composition and construction vary greatly from those of well-studied model organisms. In this work, we identify and characterize some of the proteins that regulate the mycobacterial cell wall. We find that some of these regulators appear to be functionally conserved with their structural homologs in evolutionarily distant species such as , but other proteins have critical regulatory functions that may be unique to the actinomycetes.

Delineating FtsQ-mediated regulation of cell division in Mycobacterium tuberculosis

“…We do not yet know the implications of these findings. One of the four interacting partners that was consistently found is a recently characterized cell division protein, SepIVA (24). Similar to Wag31, SepIVA has a characteristic DivIVA domain, found in cell division proteins across the bacterial kingdom (47).…”

“…We have consistently identified interaction between FtsQ and SepIVA, a recently identified cell division protein that contains a DivIVA domain (24). DivIVA domain-containing proteins are membrane curvature-sensitive proteins (49).…”

“…Although the mycobacterium lacks specialized systems to ensure the accurate positioning of divisome, the combination of directional chromosome translocation and unequal bipolar growth has been suggested as a compensatory mechanism (22). Although homologs of FtsZ, FtsK, FtsB, FtsL FtsQ, FtsI, and FtsW are annotated in mycobacteria, homologs for FtsA, ZipA, and FtsN proteins found in E. coli are lacking (23,24). The presence of these homologous proteins and a similar sequence of recruitment at the midcell suggest the partial preservation of elementary complexes and their functions in mycobacteria (24).…”

“…Although homologs of FtsZ, FtsK, FtsB, FtsL FtsQ, FtsI, and FtsW are annotated in mycobacteria, homologs for FtsA, ZipA, and FtsN proteins found in E. coli are lacking (23,24). The presence of these homologous proteins and a similar sequence of recruitment at the midcell suggest the partial preservation of elementary complexes and their functions in mycobacteria (24). In mycobacteria, FtsZ is the first protein to assemble at the midcell; it polymerizes and serves as an initiating site for recruitment of peptidoglycan (PG)-remodeling proteins (25).…”

“…A homolog of FtsK in Mycobacterium smegmatis (Msmeg) plays a role in translocation of chromosome prior to cytokinesis (22). In addition to the conserved proteins, other nonconserved proteins such as CrgA, Ssd, SepF, and SepIVA have been identified to be involved in division (24,27,28). CrgA has been shown to interact with various other divisome members like FtsZ, FtsI, PbpA, FtsQ, and CwsA, suggesting a complex and intertwined regulatory circuit (27).…”