Miller Eric, Garcia Tzintzuni, Hultgren Scott, Oberhauser Andres F
Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Biophys J. 2006 Nov 15;91(10):3848-56. doi: 10.1529/biophysj.106.088989. Epub 2006 Sep 1.
The first step in the encounter between a host and a pathogen is attachment to the host epithelium. For uropathogenic Escherichia coli, these interactions are mediated by type 1 and P adhesive pili, which are long (approximately 1 microm) rods composed of more than 1000 protein subunits arranged in a helical structure. Here we used single-molecule atomic force microscopy to study the mechanical properties of type 1 pili. We found that type 1 pili readily extend under an applied force and that this extensibility is the result of unwinding the pilus rod's helical quaternary structure. The forced unraveling is also reversible, with helical rewinding taking place under considerable forces (approximately 60 pN). These data are similar to those obtained on P pili using optical tweezers, indicating that these are conserved properties of uropathogenic E. coli pili. We also show that our data can readily be reproduced using Monte Carlo simulation techniques based on a two-state kinetic model. This model provides a simple way to extrapolate the mechanical behavior of pili under a wide range of forces. We propose that type 1 pilus unraveling is an essential mechanism for absorbing physiological shear forces encountered during urinary tract infections and probably essential for adhesion and colonization of the bladder epithelium.
宿主与病原体相遇的第一步是附着于宿主上皮细胞。对于尿路致病性大肠杆菌而言，这些相互作用是由1型菌毛和P菌毛介导的，它们是长约1微米的杆状结构，由1000多个蛋白质亚基以螺旋结构排列组成。在此，我们使用单分子原子力显微镜研究1型菌毛的力学特性。我们发现，1型菌毛在施加力的作用下很容易伸展，这种伸展性是菌毛杆螺旋四级结构解旋的结果。这种强制解旋也是可逆的，在相当大的力（约60皮牛）作用下会发生螺旋重新缠绕。这些数据与使用光镊对P菌毛获得的数据相似，表明这些是尿路致病性大肠杆菌菌毛的保守特性。我们还表明，基于双态动力学模型的蒙特卡罗模拟技术能够很容易地重现我们的数据。该模型提供了一种简单的方法来推断菌毛在广泛力作用下的力学行为。我们提出，1型菌毛解旋是吸收尿路感染期间遇到的生理剪切力的一种重要机制，可能对膀胱上皮细胞的黏附和定植至关重要。
