Structural insights into the dimerization of the response regulator ComE from Streptococcus pneumoniae

Abstract

Natural transformation contributes to the maintenance and to the evolution of the bacterial genomes. In Streptococcus pneumoniae, this function is reached by achieving the competence state, which is under the control of the ComD-ComE two-component system. We present the crystal and solution structures of ComE. We mimicked the active and non-active states by using the phosphorylated mimetic ComED58E and the unphosphorylatable ComED58A mutants. In the crystal, full-length ComED58A dimerizes through its canonical REC receiver domain but with an atypical mode, which is also adopted by the isolated RECD58A and RECD58E. The LytTR domain adopts a tandem arrangement consistent with the two direct repeats of its promoters. However ComED58A is monomeric in solution, as seen by SAXS, by contrast to ComED58E that dimerizes. For both, a relative mobility between the two domains is assumed. Based on these results we propose two possible ways for activation of ComE by phosphorylation. © 2014 © The Author(s) 2014. Published by Oxford University Press.