Tziatzios Christos, Schubert Dieter, Lotz Mirko, Gundogan Derya, Betz Heidi, Schägger Hermann, Haase Winfried, Duong Franck, Collinson Ian
Institute für Biophysik, JWG-Universität, 60590 Frankfurt am Main, Germany.
J Mol Biol. 2004 Jul 9;340(3):513-24. doi: 10.1016/j.jmb.2004.04.076.
In bacteria, the Sec-protein transport complex facilitates the passage of most secretory and membrane proteins across and into the plasma membrane. The core complex SecYEG forms the protein channel and engages either ribosomes or the ATPase SecA, which drive translocation of unfolded polypeptide chains through the complex and into the periplasmic space. Escherichia coli SecYEG forms dimers in membranes, but in detergent solution the population of these dimers is low. However, we find that stable dimers can be assembled by the addition of a monoclonal antibody. Normally, a stable SecYEG-SecA complex can only form on isolated membranes or on reconstituted proteo-liposomes. The antibody-stabilised SecYEG dimer binds one SecA molecule in detergent solution. In the presence of AMPPNP, a non-hydrolysable analogue of ATP, a complex forms containing one antibody and two each of SecYEG and SecA. SecYEG monomers or tetramers do not associate to a significant degree with SecA. The observed variability in the stoichiometry of SecYEG and SecA association and its nucleotide modulation may be important and necessary for the protein translocation reaction.
在细菌中，Sec 蛋白转运复合体促进大多数分泌蛋白和膜蛋白穿过并进入质膜。核心复合体 SecYEG 形成蛋白质通道，并与核糖体或 ATP 酶 SecA 结合，后者驱动未折叠的多肽链通过该复合体转运至周质空间。大肠杆菌 SecYEG 在膜中形成二聚体，但在去污剂溶液中这些二聚体的数量较少。然而，我们发现通过添加单克隆抗体可以组装出稳定的二聚体。通常，稳定的 SecYEG-SecA 复合体只能在分离的膜或重组的蛋白脂质体上形成。抗体稳定的 SecYEG 二聚体在去污剂溶液中结合一个 SecA 分子。在 ATP 的非水解类似物 AMPPNP 存在下，会形成一种复合体，其中包含一个抗体以及各两个 SecYEG 和 SecA。SecYEG 单体或四聚体与 SecA 的结合程度不显著。观察到的 SecYEG 和 SecA 结合化学计量比的变化及其核苷酸调节对于蛋白质转运反应可能是重要且必要的。
