COMPLEXES BETWEEN SECA AND SECB, PROTEINS INVOLVED IN PROTEIN EXPORT

该子项目是利用 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得主要资金， 因此可以在其他CRISP条目中表示。列出的机构是 中心，不一定是研究者的机构。 蛋白质在E.大肠杆菌中的蛋白质是由一般的分泌或Sec系统介导的，该系统包括穿过膜的通道、SecYEG、马达ATP酶、SecA和伴侣SecB。 我们对SecA和SecB之间的对接感兴趣。我们的研究的基础上分析离心和静态光散射与尺寸排阻色谱法表明，活性SecA：SecB复合物具有化学计量的两个SecA的protomer绑定到四聚体SecB。除了作为伴侣蛋白的功能外，SecB还将SecA的ATP酶活性与有效的易位偶联。我们有突变体，其以一个SecA原聚体与一个SecB四聚体的化学计量填充复合物，并且它们在偶联中有缺陷。我们的研究与定点自旋标记和电子顺磁共振光谱已定义SecA和SecB之间的接触区域。然而，我们不能确定SecB相对于SecA亚基的方向。如果我们能获得这些复合物的整体形状，我们试图了解耦合机制将大大方便。SecA马达在所有细菌物种中是保守的，因此其功能受到广泛关注。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Protein translocation through the cytoplasmic membrane in E. coli is mediated by the general secretory or Sec system that comprises a channel through the membrane, SecYEG, a motor ATPase, SecA and a chaperone SecB. We are interested in the docking between SecA and SecB. Our studies based on analytical centrifugation and static light scatter in line with size exclusion chromatography indicate that the active SecA : SecB complex has the stoichiometry of two SecA protomers bound to the tetrameric SecB. In addition to its function as a chaperone, SecB couples the ATPase activity of SecA to efficient translocation. We have mutants that populate a complex with a stoichiometry of one SecA protomer to a SecB tetramer and they are defective in the coupling. Our studies with site-directed spin labeling and electron paramagnetic resonance spectroscopy have defined regions of contact between SecA and SecB. However we can not determine the orientation of SecB relative to the SecA subunits. If we could obtain the overall shape of these complexes our attempts to understand the mechanism of coupling would be greatly facilitated. The SecA motor is conserved in all bacterial species and thus its function is of wide interest.