Secretion and assembly of regular surface structures in Gram-negative bacteria

Abstract

Bacteria synthesize large-sized surface structures through the ordered polymerization of protein subunits. This results in planar or tubular regular structures that have evolved to accomplish specific functions related to the particular environment in which these bacteria are found. Tubular assemblies known as flagella are the most complex structures known in bacteria and consist of a helical rigid filament, a torsion adapter or hook and a proton-fueled rotator known as the basal body. Pili or fimbriae are less complicated helical filaments, which consist of a major subunit and 3-5 minor subunits or pilins, whose main function is the attachment to specific surfaces. Planar structures known as S-layers are the simplest of these regular assemblies and are generally made up of a single subunit packed as a bidimensional crystal around the whole cell surface. Most of the components of these structures have to be secreted through the inner membrane (IM), the periplasm and the outer membrane (OM) before reaching their final destination. The so called general secretory pathway (GSP), or type II secretion system, appears to be implicated in this process to varying degrees, depending on the structure considered. A few S-layers and pili require GSP components but also need specific terminal branches, such as the well known chaperone-usher pathway. On the other hand, only two of the nearly 40 proteins involved in flagellar assembly are dependent on the GSP, while the external components are secreted through a specific pathway similar to the type III systems identified in some pathogens. Moreover, secretion of subunits of S-layers using dedicated type I machinery, without the involvement of any GSP component, has also been observed.

The interaction of macrophage receptors with bacterial ligands

“…The filament forms the major component of the flagella and this is made up of a polymer of a single protein, flagellin (Ref. 35). In bacteria such as Salmonella, variations in flagellar structure, together with LPS, give rise to antigenic variations resulting in different bacterial serotypes (Ref.…”

Proteomic comparison of membrane and extracellular proteins from invasive (PAO1) and cytotoxic (6206) strains of Pseudomonas aeruginosa

“…Although these proteins are probably due to cell autolysis [35], the presence of membrane and intracellular proteins in the extracellular environment may also be due to exocytosis, in which small portions of the outer membrane and periplasm form esicles that are released into the extracellular environment [42][43]. The role of membrane vesicles secreted by bacteria has not been well established, but such vesicles have been shown to package proteases including alkaline phosphatase, beta-lactamase, hydrolases or DNA, suggesting that they may be important in pathogenic processes and/or transfer of DNA to other cells [43][44][45]. Obviously, a membrane protein localized to the portion of membrane forming a vesicle will be incorporated into the vesicle, which is small enough to pass through the 0.2 micron filter used in this study.…”

Importance of Campylobacter jejuni FliS and FliW in Flagella Biogenesis and Flagellin Secretion

“…The flagellar hook forms a curved protein filament that under the right angle connects the basal body with the flagellar filament, enabling efficient rotation of the flagellum. The mature filament that protrudes from the bacterial surface may consist of as many as 20,000 copies of one or more flagellin subunit proteins (Fernández and Berenguer, 2000; Evans et al, 2014). Structural analysis of bacterial flagellins indicates that the proteins are folded into distinct morphological domains, D0–D3 (Vonderviszt et al, 1991; Samatey et al, 2001).…”