Effects of pH and ionic strength on the assembly and bundling of FtsZ protofilaments: a possible role of electrostatic interactions in the bundling of protofilaments

摘要

Assembly, bundling and stability of FtsZ protofilaments are important for the formation and functioning of the cytokinetic Z-ring during bacterialdivision. We found that the bundling of FtsZ protofilaments decreased strongly with increasing pH from 6.0 to 7.9, while the assembly of FtsZmonomers did not decrease considerably. In addition, the disassembly of FtsZ protofilaments was strongly suppressed at pH 6.0 as compared tothe elevated pHs. The far-UV circular dichroism spectra of the native FtsZ and the tryptophan emission spectra of mutated FtsZ (Y371W) did notchange by increasing pH from 6 to 7.9 indicating that the structure of FtsZ was not altered significantly. Further, the inhibition of bundling of FtsZprotofilaments predominantly, and the inhibition of assembly to a lesser extent by salt indicated that electrostatic interactions are important forthe assembly and bundling of FtsZ protofilaments. These observations are supported by the results of computational docking of Escherichia colidimer structure. The results suggest that the basic intracellular pH (7.4–7.8) of E. coli may play a role in regulating the assembly dynamics of FtsZin the Z-ring by reducing protofilament stability and bundling in bacterial cytoplasm.