Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas 66045, USA.
J Biol Chem. 2012 Jul 20;287(30):25303-11. doi: 10.1074/jbc.M112.381574. Epub 2012 May 31.
The type III secretion system (T3SS) is essential in the pathogenesis of many bacteria. The inner rod is important in the assembly of the T3SS needle complex. However, the atomic structure of the inner rod protein is currently unknown. Based on computational methods, others have suggested that the Salmonella inner rod protein PrgJ is highly helical, forming a folded 3 helix structure. Here we show by CD and NMR spectroscopy that the monomeric form of PrgJ lacks a tertiary structure, and the only well-structured part of PrgJ is a short α-helix at the C-terminal region from residues 65-82. Disruption of this helix by glycine or proline mutation resulted in defective assembly of the needle complex, rendering bacteria incapable of secreting effector proteins. Likewise, CD and NMR data for the Shigella inner rod protein MxiI indicate this protein lacks a tertiary structure as well. Our results reveal that the monomeric forms of the T3SS inner rod proteins are partially folded.
III 型分泌系统（T3SS）在许多细菌的发病机制中是必不可少的。内杆在 T3SS 针复合物的组装中很重要。然而，内杆蛋白的原子结构目前尚不清楚。基于计算方法，其他人已经表明，沙门氏菌内杆蛋白 PrgJ 高度螺旋，形成折叠的 3 螺旋结构。在这里，我们通过 CD 和 NMR 光谱表明，PrgJ 的单体形式缺乏三级结构，PrgJ 唯一结构良好的部分是 C 末端残基 65-82 处的短 α-螺旋。通过甘氨酸或脯氨酸突变破坏该螺旋会导致针复合物组装缺陷，使细菌无法分泌效应蛋白。同样，志贺氏菌内杆蛋白 MxiI 的 CD 和 NMR 数据表明，该蛋白也没有三级结构。我们的结果表明，T3SS 内杆蛋白的单体形式部分折叠。
