Metal-dependent SpollE oligomerization stabilizes FtsZ during asymmetric division in Bacillus subtilis

SpollE is a bifunctional protein involved in asymmetric septum formation and in activation of the forespore compartment-specific transcription factor sigma(F) through dephosphorylation of Spot IAA-P. The phosphatase activity of SpollE requires Mn2+ as a metal cofactor. Here, we show that the presence of a metal cofactor also influences SpollE oligomerization and asymmetric septum formation. Absence of Mn2+ from sporulation medium results in a delay of the formation of polar FtsZ-rings, similar to a spollE null mutant. We purified the entire cytoplasmic part of the SpollE protein, and show that the protein copurifies with bound metals. Metal binding both stimulates SpollE oligomerization, and results in the formation of larger oligomeric structures. The presence of SpollE oligomers reduces FtsZ GTP hydrolysis activity and stabilizes FtsZ polymers in a light scattering assay. Combined, these results indicate that metal binding is not just required for SpollE phosphatase activity but also is important for SpollE's role in asymmetric septum formation.