Structural insights into the secretin PulD and its trypsin-resistant core
Structural insights into the secretin PulD and its trypsin-resistant core
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DOI：
10.1074/jbc.m504463200
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发表时间：
2005-11-11
影响因子：
4.8
通讯作者：
Bayan, N
中科院分区：
文献类型：
--
作者：
Chami, M;Guilvout, I;Bayan, N
通过扫描透射电子显微镜结合了有限的蛋白水解，二级结构和生化分析，质谱法和质谱测量，并与冷冻电子显微镜结合使用，以生成由外膜puld，一种基本通道Puld（一种基本通道）的同型同型复合物的三维模型，来自Klebsiella oxytoca的II型分泌系统的成分。该络合物是由两个环组成的十二体结构，这些环将封闭的圆盘夹住。两个环在中央插头的两侧形成了中间盘的一部分。 PULD多肽包括两个主要的，结构上完全不同的结构域。一个n域，形成了一个腔室的墙壁，以及一个耐胰蛋白酶的C域，该域有助于外室，中央盘和塞子。与经典外膜蛋白相比，C结构域的潜在跨膜β结构的比例较低，这表明只有一小部分嵌入了外膜内。实际上，C结构域可能远远超出了外膜双层的范围，形成了一个中央塞的通道，该通道均渗透到周质侧的肽聚糖，以及细胞表面上的脂多糖和胶囊层。建议内部腔室构成一个分泌的脱蛋白蛋白酶的对接部位，而外腔室可以允许插头的位移以打开通道并允许摄取蛋白逸出。
Limited proteolysis, secondary structure and biochemical analyses, mass spectrometry, and mass measurements by scanning transmission electron microscopy were combined with cryo-electron microscopy to generate a three-dimensional model of the homomultimeric complex formed by the outer membrane secretin PulD, an essential channel-forming component of the type II secretion system from Klebsiella oxytoca. The complex is a dodecameric structure composed of two rings that sandwich a closed disc. The two rings form chambers on either side of a central plug that is part of the middle disc. The PulD polypeptide comprises two major, structurally quite distinct domains; an N domain, which forms the walls of one of the chambers, and a trypsin-resistant C domain, which contributes to the outer chamber, the central disc, and the plug. The C domain contains a lower proportion of potentially transmembrane beta-structure than classical outer membrane proteins, suggesting that only a small part of it is embedded within the outer membrane. Indeed, the C domain probably extends well beyond the confines of the outer membrane bilayer, forming a centrally plugged channel that penetrates both the peptidoglycan on the periplasmic side and the lipopolysaccharide and capsule layers on the cell surface. The inner chamber is proposed to constitute a docking site for the secreted exoprotein pullulanase, whereas the outer chamber could allow displacement of the plug to open the channel and permit the exoprotein to escape.