Abstract
Cytokinesis in bacteria depends upon the contractile Z ring, which is composed of dynamic polymers of the tubulin homolog FtsZ as well as other membrane-associated proteins such as FtsA, a homolog of actin that is required for membrane attachment of the Z ring and its subsequent constriction. Here we show that a previously characterized hypermorphic mutant FtsA (FtsA*) partially disassembled FtsZ polymers in vitro. This effect was strictly dependent on ATP or ADP binding to FtsA* and occurred at substoichiometric levels relative to FtsZ, similar to cellular levels. Nucleotide-bound FtsA* did not affect FtsZ GTPase activity or the critical concentration for FtsZ assembly but was able to disassemble preformed FtsZ polymers, suggesting that FtsA* acts on FtsZ polymers. Microscopic examination of the inhibited FtsZ polymers revealed a transition from long, straight polymers and polymer bundles to mainly short, curved protofilaments. These results indicate that a bacterial actin, when activated by adenine nucleotides, can modify the length distribution of bacterial tubulin polymers, analogous to the effects of actin-depolymerizing factor/cofilin on F-actin.
Highlights
Bacterial cell division requires a large number of proteins that colocalize to form a putative protein machine at the cell membrane [1]
In E. coli, the FtsA:FtsZ ratio is crucial for proper cell division, with either too high or too low a ratio inhibiting septum formation [26, 27]
The R286W and E124A mutants of FtsA bypass the FtsA:FtsZ ratio rule, allowing cell division to occur at higher ratios than with WT2 FtsA
Summary
Bacterial cell division requires a large number of proteins that colocalize to form a putative protein machine at the cell membrane [1]. We show that FtsA*, at physiological concentrations in the presence of ATP or ADP, has significant effects on the assembly of FtsZ filaments. Sedimentation Assay—Purified FtsZ (12 M) was polymerized in FtsZ assembly buffer (25 mM PIPES, pH 7.4, with 10 mM MgCl2 and 100 mM potassium glutamate) plus 2 mM GTP and HT-FtsA* (0 –5 M), in the absence or presence of 2 mM ATP, ADP, or AMPPNP.
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