Surface organelles assembled by secretion systems of Gram-negative bacteria: diversity in structure and function

Abstract

Gram-negative bacteria express a wide variety of organelles on their cell surface. These surface structures may be the end products of secretion systems, such as the hair-like fibers assembled by the chaperone/usher and type IV pilus pathways, which generally function in adhesion to surfaces and bacterial-bacterial and bacterial-host interactions. Alternatively, the surface organelles may be integral components of the secretion machinery itself, such as the needle complex and pilus extensions formed by the type III and type IV secretion systems, which function in the delivery of bacterial effectors inside host cells. Bacterial surface structures perform functions critical for pathogenesis and have evolved to withstand forces exerted by the external environment and cope with defenses mounted by the host immune system. Given their essential roles in pathogenesis and exposed nature, bacterial surface structures also make attractive targets for therapeutic intervention. This review will describe the structure and function of surface organelles assembled by four different Gram-negative bacterial secretion systems: the chaperone/usher pathway, the type IV pilus pathway, and the type III and type IV secretion systems.

Pathogenesis of Human Enterovirulent Bacteria: Lessons from Cultured, Fully Differentiated Human Colon Cancer Cell Lines

“…The flagella of enterovirulent bacteria have been shown to be necessary for colonizing the intestine, crossing the intestinal mucus layer and then attaching to epithelial cells, and promoting early innate host responses. Human enterovirulent bacteria display huge genetic diversity, and have evolved a wide repertoire of virulence and colonization factors that facilitate host-pathogen interactions with the apical domain of the fully differentiated polarized epithelial cells and M cells that line the intestinal epithelial barrier (259)(260)(261)(262)(263)(264)(265). Moreover, human intestinal bacterial pathogens are equipped with a variety of weapons that provide them with a variety of mechanisms for subverting the cellular machinery and circumventing host defenses.…”

“…The biogenesis and regulation of bacterial adhesins in both intestinal and extraintestinal bacterial pathogens have been studied in detail (259)(260)(261)(262)(263)(264)(265). Attachment to host intestinal cells is a way of avoiding being dislodged by mucosal secretions and peristalsis, and enterovirulent bacteria produce a wide variety of adhesive structures or factors, including, for example, nonfimbrial and fimbrial polymeric structures that extend out from the bacterial surface and allow them to interact at a distance from the cells.…”

The archaic chaperone–usher pathways may depend on donor strand exchange for intersubunit interactions

“…Three-day-old spores of wt and mcuC mutant strains were collected, fractionated into S100, P100S and P100P as described in Methods, and examined by immunoblotting using antiserum against protein S. M, Protein markers. DSE (Poole et al, 2007;Thanassi et al, 2012 (Fig. 3b).…”

Molecular mechanism of bacterial type 1 and P pili assembly

“…The F1 pili are produced by Yersinia pestis via the Caf1 CU pathway, and the CFA/I pili are assembled in enterotoxigenic E. coli (ETEC) via the alternate CU pathway (figure 1). Besides the CU pathways, there are two other pili assembly pathways: (i) the curli biogenesis or nucleation/precipitation pathway and (ii) the type IV pilus assembly pathway (for details, please see reviews [6,7]). In this review, we essentially focus on structural, mechanistic and kinetic insights gained on the type 1 (Fim) and P (Pap) pili, which are mainly found in UPEC strains and are mostly involved in the development of highly recurrent urinary tract infections (UTIs) such as cystitis (type 1 pilus) or pyelonephritis (P pilus).…”