Abstract
We have studied the influence of protein crowders, either combined or individually, on the GTP-induced FtsZ cooperative assembly, crucial for the formation of the dynamic septal ring and, hence, for bacterial division. It was earlier demonstrated that high concentrations of inert polymers like Ficoll 70, used to mimic the crowded cellular interior, favor the assembly of FtsZ into bundles with slow depolymerization. We have found, by fluorescence anisotropy together with light scattering measurements, that the presence of protein crowders increases the tendency of FtsZ to polymerize at micromolar magnesium concentration, being the effect larger with ovomucoid, a negatively charged protein. Neutral polymers and a positively charged protein also diminished the critical concentration of assembly, the extent of the effect being compatible with that expected according to pure volume exclusion models. FtsZ polymerization was also observed to be strongly promoted by a negatively charged polymer, DNA, and by some unrelated polymers like PEGs at concentrations below the crowding regime. The influence of mixed crowders mimicking the heterogeneity of the intracellular environment on the tendency of FtsZ to assemble was also studied and nonadditive effects were found to prevail. Far from exactly reproducing the bacterial cytoplasm environment, this approach serves as a simplified model illustrating how its intrinsically crowded and heterogeneous nature may modulate FtsZ assembly into a functional Z-ring.
Highlights
FtsZ, an essential protein required for division in most bacteria, forms a ring (Z-ring) at midcell thought to be responsible for initiating and driving cell constriction [1,2]
To study the influence of macromolecular crowding on FtsZ assembly, we analyzed the polymerization of FtsZ in solutions containing high concentrations of unrelated proteins or inert polymers
A decrease of the concentration of polymerization (Cc) was observed at the same concentration of the inert polymers Ficoll 70 and dextran T40 and of the osmolyte sucrose, under our experimental conditions (Fig 1A and Table 1)
Summary
FtsZ, an essential protein required for division in most bacteria, forms a ring (Z-ring) at midcell thought to be responsible for initiating and driving cell constriction [1,2]. In the presence of GDP, FtsZ exhibits isodesmic oligomerization in a KCl and Mg2+ dependent manner [3]. The cooperative assembly of FtsZ into polymers, linked to its GTPase activity, has been extensively studied in vitro, especially for Escherichia coli FtsZ [2,4]. Addition of GTP triggers, above the PLOS ONE | DOI:10.1371/journal.pone.0149060. Charge Modulation of Crowding Effects on FtsZ Polymerization Addition of GTP triggers, above the PLOS ONE | DOI:10.1371/journal.pone.0149060 February 12, 2016
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