Ectopic positioning of the cell division plane is associated with single amino acid substitutions in the FtsZ-recruiting SsgB in Streptomyces.

Xiansha Xiao,Meindert Lamers,Joost Willemse,Andrea E Prota,Gilles P Van Wezel,Xinmeng Li,Patrick Voskamp,Navraj Pannu,Jan Pieter Abrahams

doi:10.1098/rsob.200409

Abstract

In most bacteria, cell division begins with the polymerization of the GTPase FtsZ at mid-cell, which recruits the division machinery to initiate cell constriction. In the filamentous bacterium Streptomyces, cell division is positively controlled by SsgB, which recruits FtsZ to the future septum sites and promotes Z-ring formation. Here, we show that various amino acid (aa) substitutions in the highly conserved SsgB protein result in ectopically placed septa that sever spores diagonally or along the long axis, perpendicular to the division plane. Fluorescence microscopy revealed that between 3.3% and 9.8% of the spores of strains expressing SsgB E120 variants were severed ectopically. Biochemical analysis of SsgB variant E120G revealed that its interaction with FtsZ had been maintained. The crystal structure of Streptomyces coelicolor SsgB was resolved and the key residues were mapped on the structure. Notably, residue substitutions (V115G, G118V, E120G) that are associated with septum misplacement localize in the α2-α3 loop region that links the final helix and the rest of the protein. Structural analyses and molecular simulation revealed that these residues are essential for maintaining the proper angle of helix α3. Our data suggest that besides altering FtsZ, aa substitutions in the FtsZ-recruiting protein SsgB also lead to diagonally or longitudinally divided cells in Streptomyces.

Highlights

During bacterial cell division, the tubulin homologue FtsZ is the first component recruited to the division site, where it polymerizes into a ring-like structure known as the Z-ring, which contracts during cytokinesis [1]
We analysed the effect of amino acid substitutions in ssgB on cell division and morphogenesis, using S. coelicolor as the model system
Inspired by the extremely high conservation of the SsgB protein in Streptomyces species, with natural variants only found in aa 128 (Q, R or temperature-sensitive ftsz26 (Ts)), we studied the effect of point mutations in the protein on cell division and morphogenesis of the model strain S. coelicolor

Summary

Introduction

The tubulin homologue FtsZ is the first component recruited to the division site, where it polymerizes into a ring-like structure known as the Z-ring, which contracts during cytokinesis [1]. The treadmilling is associated with the conformational change and the kinetic polarity of the FtsZ filament and controls the rate of PG synthesis and cell division [8,10]. Septum-site localization in unicellular bacteria depends on FtsA and ZipA, which anchor FtsZ polymers to the cell membrane, with ZapA stabilizing the FtsZ filaments and promoting lateral interactions [11,12,13]. In Escherichia coli, control of Z-ring timing and localization is governed by the Min system and by nucleoid occlusion, which negatively regulate FtsZ polymerization [14,15,16,17]

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Results

Discussion

Conclusion