Zhang Lingling, Wang Yu, Picking Wendy L, Picking William D, De Guzman Roberto N
Department of Molecular Biosciences, The University of Kansas, 1200 Sunnyside Avenue, Lawrence, KS 66045, USA.
J Mol Biol. 2006 Jun 2;359(2):322-30. doi: 10.1016/j.jmb.2006.03.028. Epub 2006 Mar 30.
Many gram-negative bacteria that are important human pathogens possess type III secretion systems as part of their required virulence factor repertoire. During the establishment of infection, these pathogens coordinately assemble greater than 20 different proteins into a macromolecular structure that spans the bacterial inner and outer membranes and, in many respects, resembles and functions like a syringe. This type III secretion apparatus (TTSA) is used to inject proteins into a host cell's membrane and cytoplasm to subvert normal cellular processes. The external portion of the TTSA is a needle that is composed of a single type of protein that is polymerized in a helical fashion to form an elongated tube with a central channel of 2-3 nm in diameter. TTSA needle proteins from a variety of bacterial pathogens share sequence conservation; however, no atomic structure for any TTSA needle protein is yet available. Here, we report the structure of a TTSA needle protein called BsaL from Burkholderia pseudomallei determined by nuclear magnetic resonance (NMR) spectroscopy. The central part of the protein assumes a helix-turn-helix core domain with two well-defined alpha-helices that are joined by an ordered, four-residue linker. This forms a two-helix bundle that is stabilized by interhelix hydrophobic contacts. Residues that flank this presumably exposed core region are not completely disordered, but adopt a partial helical conformation. The atomic structure of BsaL and its sequence homology with other TTSA needle proteins suggest potentially unique structural dynamics that could be linked with a universal mechanism for control of type III secretion in diverse gram-negative bacterial pathogens.
许多作为重要人类病原体的革兰氏阴性菌都拥有III型分泌系统，这是其所需毒力因子库的一部分。在感染确立过程中，这些病原体协同将20多种不同蛋白质组装成一个跨越细菌内膜和外膜的大分子结构，在许多方面，该结构类似于注射器并发挥着类似注射器的功能。这种III型分泌装置（TTSA）用于将蛋白质注入宿主细胞膜和细胞质中，以颠覆正常的细胞过程。TTSA的外部是一根针，由单一类型的蛋白质组成，该蛋白质以螺旋方式聚合形成一个细长的管子，其中心通道直径为2-3纳米。来自多种细菌病原体的TTSA针蛋白具有序列保守性；然而，尚无任何TTSA针蛋白的原子结构。在此，我们报告了通过核磁共振（NMR）光谱法测定的来自类鼻疽伯克霍尔德菌的一种名为BsaL的TTSA针蛋白的结构。该蛋白的中心部分呈现出一个螺旋-转角-螺旋核心结构域，有两个定义明确的α螺旋，由一个有序的四残基连接子连接。这形成了一个双螺旋束，通过螺旋间的疏水接触得以稳定。位于这个可能暴露的核心区域两侧的残基并非完全无序，而是呈现出部分螺旋构象。BsaL的原子结构及其与其他TTSA针蛋白的序列同源性表明，可能存在独特的结构动力学，这可能与多种革兰氏阴性细菌病原体中III型分泌的通用控制机制相关。
