Interplay of the Serine/Threonine-Kinase StkP and the Paralogs DivIVA and GpsB in Pneumococcal Cell Elongation and Division

Abstract

Despite years of intensive research, much remains to be discovered to understand the regulatory networks coordinating bacterial cell growth and division. The mechanisms by which Streptococcus pneumoniae achieves its characteristic ellipsoid-cell shape remain largely unknown. In this study, we analyzed the interplay of the cell division paralogs DivIVA and GpsB with the ser/thr kinase StkP. We observed that the deletion of divIVA hindered cell elongation and resulted in cell shortening and rounding. By contrast, the absence of GpsB resulted in hampered cell division and triggered cell elongation. Remarkably, ΔgpsB elongated cells exhibited a helical FtsZ pattern instead of a Z-ring, accompanied by helical patterns for DivIVA and peptidoglycan synthesis. Strikingly, divIVA deletion suppressed the elongated phenotype of ΔgpsB cells. These data suggest that DivIVA promotes cell elongation and that GpsB counteracts it. Analysis of protein-protein interactions revealed that GpsB and DivIVA do not interact with FtsZ but with the cell division protein EzrA, which itself interacts with FtsZ. In addition, GpsB interacts directly with DivIVA. These results are consistent with DivIVA and GpsB acting as a molecular switch to orchestrate peripheral and septal PG synthesis and connecting them with the Z-ring via EzrA. The cellular co-localization of the transpeptidases PBP2x and PBP2b as well as the lipid-flippases FtsW and RodA in ΔgpsB cells further suggest the existence of a single large PG assembly complex. Finally, we show that GpsB is required for septal localization and kinase activity of StkP, and therefore for StkP-dependent phosphorylation of DivIVA. Altogether, we propose that the StkP/DivIVA/GpsB triad finely tunes the two modes of peptidoglycan (peripheral and septal) synthesis responsible for the pneumococcal ellipsoid cell shape.

Pneumococcal meningitis is promoted by single cocci expressing pilus adhesin RrgA

“…The pneumococcal protein DivIVA is one of a number of membrane proteins that orchestrate and fine tune cell wall synthesis during septal growth and cell separation and localize to the division septum and to the poles of cocci (21,22). It has been proposed that DivIVA tunes the 2 modes of peptidoglycan (peripheral and septal) synthesis in pneumococci and is responsible for the cell's ovoid shape (22).…”

“…It has been proposed that DivIVA tunes the 2 modes of peptidoglycan (peripheral and septal) synthesis in pneumococci and is responsible for the cell's ovoid shape (22). Deletion of DivIVA hindered cell elongation and resulted in cell shortening and rounding (22).…”

“…It has been proposed that DivIVA tunes the 2 modes of peptidoglycan (peripheral and septal) synthesis in pneumococci and is responsible for the cell's ovoid shape (22). Deletion of DivIVA hindered cell elongation and resulted in cell shortening and rounding (22). We investigated the expression of DivIVA and the structural pilus proteins RrgA, RrgB, and RrgC in brain homogenates from mice infected with the 3 clinical isolates of serotype 6B, TIGR4, or TIGR4ΔrrgA-srtD.…”

Roles of the Essential Protein FtsA in Cell Growth and Division in Streptococcus pneumoniae

“…First, proteins within peripheral and septal PG synthesis complexes all localize to midcell (33)(34)(35)(36). Second, inactivation or depletion of proteins that function late in cell division (e.g., for septum remodeling or closure) are associated with a variety of phenotypes but not cell lysis (39,40,47,60,62,64), whereas those involved in peripheral or septal PG synthesis result in cell lysis, independently of the respective protein's role in cell elongation or cell division (40, 41, 44, 65, 66). This correlation underscores the intimate coordination and chronology between the two PG biosynthetic machineries (34)(35)(36)43).…”

“…B. subtilis cells lacking GpsB do not show any distinctive phenotype but cannot grow when FtsA is simultaneously inactivated (61). In S. pneumoniae, GpsB, like FtsA, is essential in the progenitor D39 genetic background (40,62), whereas Rx1 ΔgpsB mutants are viable because of the presence of preexisting suppressors in the laboratory strain genetic background but that grow very slowly (Rued et al, unpublished data). Attempts to transform a ΔgpsB deletion amplicon into a D39 Δcps ftsA ϩ //P Zn ftsA ϩ merodiploid strain overexpressing FtsA in the presence of 0.5 mM ZnCl 2 plus 0.05 mM MnSO 4 were unsuccessful (data not shown), implying that overproduction of FtsA alone does not suppress the requirement for GpsB in this strain.…”