Structural insights into the biogenesis and biofilm formation by the Escherichia coli common pilus

Abstract

Bacteria have evolved a variety of mechanisms for developing community-based biofilms. These bacterial aggregates are of clinical importance, as they are a major source of recurrent disease. Bacterial surface fibers (pili) permit adherence to biotic and abiotic substrates, often in a highly specific manner. The Escherichia coli common pilus (ECP) represents a remarkable family of extracellular fibers that are associated with both disease-causing and commensal strains. ECP plays a dual role in early-stage biofilm development and host cell recognition. Despite being the most common fimbrial structure, relatively little is known regarding its biogenesis, architecture, and function. Here we report atomic-resolution insight into the biogenesis and architecture of ECP. We also derive a structural model for entwined ECP fibers that not only illuminates interbacteria communication during biofilm formation but also provides a useful foundation for the design of novel nanofibers.chaperone-usher | donor-strand exchange | X-ray crystallography T he long coexistence between bacteria and their eukaryote hosts has fine-tuned their relationships. These microorganisms have developed remarkable molecular systems for the trafficking of molecules across the cell envelope and exchanging signals with their environment. Historically, bacteria have been studied during their planktonic life cycle, although a matrix-enclosed, organized-community lifestyle is a frequent mode of growth for countless species that exist in diverse environments. Many bacteria produce surface fibers allowing them to adhere to each other and to biotic and abiotic surfaces (1, 2). Furthermore, many of these fibers are able to recognize specific host cell receptors during the first steps of host colonization and subsequent biofilm formation (3). These bacterial aggregates are of clinical importance, as they are a major source of recurrent disease allowing reservoirs of bacteria to persist in a host or the environment. Biofilms also contribute to increased resistance to antibiotics, the immune system, and host clearance mechanisms (4).Escherichia coli are primarily commensal colonizers of the human and other animal bowels, contributing to a healthy host immune system. Conversely, there are a number of virulent strains that are important causative agents of many diarrheal diseases such as hemorrhagic colitis (4). Upon entering extraintestinal sites, pathogenic strains can also lead to neonatal meningitis, urinary tract infections, sepsis, and pneumonia (5). The effects of such gastrointestinal and urinary tract diseases in the developing world are considerable (6), and they are estimated to kill around 2.5 million people every year, mostly young children (7).The E. coli common pilus (ECP), encoded by the ecpRABCDE operon, is an extracellular adhesive fiber first documented in association with E. coli strains causing newborn meningitis and septicaemia (NMEC), where it was originally named the Mat (meningitis-associated and temperature-regulated) fimbriae (8). Furthe...

Purification, crystallization and preliminary X-ray diffraction analysis of theEscherichia colicommon pilus chaperone EcpB

“…Biogenesis of Ecp is via an alternative chaperone-usher (CU) pathway (Waksman & Hultgren, 2009) and all genes necessary for this can be found on a single operon composed of ecpR, ecpA, ecpB, ecpC, ecpD and ecpE (Pouttu et al, 2001;Garnett et al, 2012). EcpR is a transcriptional regulator, while EcpC is an usher pore responsible for pilus assembly and secretion, and EcpA and EcpD are both components of the pilus.…”

“…The majority of the Ecp shaft is composed of the 17.9 kDa EcpA pilin subunit. We have previously solved the X-ray crystal structure of this major pilus component and have further shown how it promotes inter-Ecp biofilm interactions through the antiparallel winding of fibres about one another (Garnett et al, 2012). EcpD is an adhesive-tip subunit that can recognize receptors on the surface of host cells.…”

“…Although different strains of E. coli have developed specific pili to enable them to thrive in their niche environments, almost all produce a surface fibre called the E. coli common pilus (Ecp; Pouttu et al, 2001;Rendó n et al, 2007;Garnett et al, 2012). This structure is involved in key processes during sessile Enterobacteriaceae lifecycles, where it mediates both host-cell adherence and early biofilm interbacterial interactions (Rendó n et al, 2007; Lehti et al, 2010;Garnett et al, 2012).…”

Escherichia coli Common Pilus (ECP) Targets Arabinosyl Residues in Plant Cell Walls to Mediate Adhesion to Fresh Produce Plants

“…ECP belongs to the chaperoneusher family encoded by the ecpRABCDE operon where EcpA encodes the pilin domain and EcpD encodes the polymerized tip adhesin. Unusually for classical tip adhesins, EcpD can be polymerized independently, which requires an N-terminal extension in EcpD, or with the major pilin domain (18). Several roles have been described for ECP, including binding to cultured human epithelial cells (16,17,20), colonization of infant mice (21), and biofilm development through interorganelle binding of EcpA (22).…”

“…The ecp operon is ubiquitous across E. coli and even conserved for some other enteric species (15)(16)(17)(18)(19). ECP belongs to the chaperoneusher family encoded by the ecpRABCDE operon where EcpA encodes the pilin domain and EcpD encodes the polymerized tip adhesin.…”