The three-dimensional structure of septum site- determining protein MinD from Pyrococcus horikoshii OT3 in complex with Mg-ADP

Background: In Escherichia coli, the cell division site is determined by th e cooperative activity of min operon products MinC, MinD, and MinE. MinC is a nonspecific inhibitor of the septum protein FtsZ, and MinE is the supres sor of MinC. MinD plays a multifunctional role. It is a membrane-associated ATPase and is a septum site-determining factor through the activation and regulation of MinC and MinE. MinD is also known to undergo a rapid pole-to- pole oscillation movement in vivo as observed by fluorescent microscopy. Results: The three-dimensional structure of the MinD-2 from Pyrococcus hori koshii OT3 (PH0612) has been determined at 2.3 Angstrom resolution by X-ray crystallography using the Se-Met MAD method. The molecule consists of a be ta sheet with 7 parallel and 1 antiparallel strands and 11 peripheral alpha helices. It contains the classical mononucleotide binding loop with bound ADP and magnesium ion, which is consistent with the suggested ATPase activi ty. Conclusions: Structure analysis shows that MinD is most similar to nitrogen ase iron protein, which is a member of the P loop-containing nucleotide tri phosphate hydrolase superfamily of proteins. Unlike nitrogenase or other me mber proteins that normally work as a dimer, MinD was present as a monomer in the crystal. Both the P-31 NMR and Malachite Green method exhibited rela tively low levels of ATPase activity. These facts suggest that MinD may wor k as a molecular switch in the multiprotein complex in bacterial cell divis ion.