Masson Soizic, Kern Thomas, Le Gouëllec Audrey, Giustini Cécile, Simorre Jean-Pierre, Callow Philip, Vernet Thierry, Gabel Frank, Zapun André
Laboratoire d'Ingénierie des Macromolécules, Institut de Biologie Structurale, UMR 5075, Université Joseph Fourier, CNRS, Commissariat à l'Energie Atomique, 38027 Grenoble, France.
J Biol Chem. 2009 Oct 2;284(40):27687-700. doi: 10.1074/jbc.M109.019471. Epub 2009 Jul 27.
DivIB(FtsQ), FtsL, and DivIC(FtsB) are enigmatic membrane proteins that are central to the process of bacterial cell division. DivIB(FtsQ) is dispensable in specific conditions in some species, and appears to be absent in other bacterial species. The presence of FtsL and DivIC(FtsB) appears to be conserved despite very low sequence conservation. The three proteins form a complex at the division site, FtsL and DivIC(FtsB) being associated through their extracellular coiled-coil region. We report here structural investigations by NMR, small-angle neutron and x-ray scattering, and interaction studies by surface plasmon resonance, of the complex of DivIB, FtsL, and DivIC from Streptococcus pneumoniae, using soluble truncated forms of the proteins. We found that one side of the "bean"-shaped central beta-domain of DivIB interacts with the C-terminal regions of the dimer of FtsL and DivIC. This finding is corroborated by sequence comparisons across bacterial genomes. Indeed, DivIB is absent from species with shorter FtsL and DivIC proteins that have an extracellular domain consisting only of the coiled-coil segment without C-terminal conserved regions (Campylobacterales). We propose that the main role of the interaction of DivIB with FtsL and DivIC is to help the formation, or to stabilize, the coiled-coil of the latter proteins. The coiled-coil of FtsL and DivIC, itself or with transmembrane regions, could be free to interact with other partners.
DivIB（FtsQ）、FtsL和DivIC（FtsB）是神秘的膜蛋白，在细菌细胞分裂过程中起着核心作用。DivIB（FtsQ）在某些物种的特定条件下是可有可无的，并且在其他细菌物种中似乎不存在。尽管序列保守性很低，但FtsL和DivIC（FtsB）的存在似乎是保守的。这三种蛋白在分裂位点形成一个复合物，FtsL和DivIC（FtsB）通过它们的细胞外卷曲螺旋区域相互关联。我们在此报告了利用蛋白质的可溶性截短形式，对肺炎链球菌的DivIB、FtsL和DivIC复合物进行的核磁共振、小角中子散射和X射线散射结构研究，以及表面等离子体共振相互作用研究。我们发现，DivIB的“豆”形中央β结构域的一侧与FtsL和DivIC二聚体的C末端区域相互作用。这一发现得到了跨细菌基因组序列比较的证实。事实上，在FtsL和DivIC蛋白较短且细胞外结构域仅由没有C末端保守区域的卷曲螺旋片段组成的物种（弯曲杆菌目）中不存在DivIB。我们提出，DivIB与FtsL和DivIC相互作用的主要作用是帮助形成或稳定后两者蛋白的卷曲螺旋。FtsL和DivIC的卷曲螺旋本身或与跨膜区域一起，可以自由地与其他伙伴相互作用。
