Structural and functional characterization of Pseudomonas aeruginosa CupB chaperones

Pseudomonas aeruginosa, an important human pathogen, is estimated to be responsible for,10% of nosocomial infections worldwide. The pathogenesis of P. aeruginosa starts from its colonization in the damaged tissue or medical devices (e. g. catheters, prothesis and implanted heart valve etc.) facilitated by several extracellular adhesive factors including fimbrial pili. Several clusters containing fimbrial genes have been previously identified on the P. aeruginosa chromosome and named cup [1]. The assembly of the CupB pili is thought to be coordinated by two chaperones, CupB2 and CupB4. However, due to the lack of structural and biochemical data, their chaperone activities remain speculative. In this study, we report the 2.5 A crystal structure of P. aeruginosa CupB2. Based on the structure, we further tested the binding specificity of CupB2 and CupB4 towards CupB1 (the presumed major pilus subunit) and CupB6 (the putative adhesin) using limited trypsin digestion and strep-tactin pull-down assay. The structural and biochemical data suggest that CupB2 and CupB4 might play different, but not redundant, roles in CupB secretion. CupB2 is likely to be the chaperone of CupB1, and CupB4 could be the chaperone of CupB4:CupB5:CupB6, in which the interaction of CupB4 and CupB6 might be mediated via CupB5

Impairment of the biomechanical compliance of P pili : a novel means of inhibiting uropathogenic bacterial infections?

Gram-negative bacteria often initiate their colonization by use of extended attachment organelles, so called pili. When exposed to force, the rod of helix-like pili has been found to be highly extendable, mainly attributed to uncoiling and recoiling of its quaternary structure. This provides the bacteria with the ability to redistribute an external force among a multitude of pili, which enables them to withstand strong rinsing flows, which, in turn, facilitates adherence and colonization processes critical to virulence. Thus, pili fibers are possible targets for novel antibacterial agents. By use of a substance that compromises compliance of the pili, the ability of bacteria to redistribute external forces can be impaired, so they will no longer be able to resist strong urine flow and thus be removed from the host. It is possible such a substance can serve as an alternative to existing antibiotics in the future or be a part of a multi-drug. In this work we investigated whether it is possible to achieve this by targeting the recoiling process. The test substance was purified PapD. The effect of PapD on the compliance of P pili was assessed at the single organelle level by use of force-measuring optical tweezers. We showed that the recoiling process, and thus the biomechanical compliance, in particular the recoiling process, can be impaired by the presence of PapD. This leads to a new concept in the search for novel drug candidates combating uropathogenic bacterial infections-"coilicides", targeting the subunits of which the pilus rod is composed

The Influence of pH on the Specific Adhesion of P Piliated Escherichia coli

Adhesion to host tissues is an initiating step in a majority of bacterial infections. In the case of Gram-negative bacteria this adhesion is often mediated by a specific interaction between an adhesin, positioned at the distal end of bacterial pili, and its receptor on the surface of the host tissue. Furthermore, the rod of the pilus, and particularly its biomechanical properties, is believed to be crucial for the ability of bacteria to withstand external forces caused by, for example, (in the case of urinary tract infections) urinary rinsing flows by redistributing the force to several pili. In this work, the adhesion properties of P-piliated E. coli and their dependence of pH have been investigated in a broad pH range by both the surface plasmon resonance technique and force measuring optical tweezers. We demonstrate that P piliated bacteria have an adhesion ability throughout the entire physiologically relevant pH range (pH 4.5 - 8). We also show that pH has a higher impact on the binding rate than on the binding stability or the biomechanical properties of pili; the binding rate was found to have a maximum around pH 5 while the binding stability was found to have a broader distribution over pH and be significant over the entire physiologically relevant pH range. Force measurements on a single organelle level show that the biomechanical properties of P pili are not significantly affected by pH