Cell Surface Proteins of Gram-positive Pathogenic Bacteria

Gram-positive pathogenic bacteria from the genera Staphylococcus, Streptococcus, Listeria and Bacillus display on their cell surfaces a plethora of cell-wall-anchored (CWA) surface proteins. The defining feature of such proteins is that they are secreted to the cell surface via the Sec secretion pathway and are covalently anchored to the cell surface by a membrane-located enzyme called sortase. This recognizes the sorting signal at the C-terminus of the nascent CWA protein and covalently joins the protein to peptidoglycan.

Proteins may be attached as single molecules or as complex arrays called pili or fimbriae. The latter are composed of pilin subunits that are attached to each other by a variant of sortase during the secretion process. When the chain is completed, the structure is then sorted to the cell wall. CWA proteins perform a variety of functions viz:
(i) adhesion to the extracellular matrix, to surfaces and to mammalian cells,
(ii) evasion of innate and adaptive immune responses,
(iii) invasion of non-phagocytic host cells by pathogen-directed endocytosis,
(iv) acquisition of iron from haemoglobin and
(v) cell-cell aggregation during biofilm formation.
Many CWA proteins are multifunctional.

CWA proteins have potential as candidate vaccine antigens and inhibitors of sortases could be developed as non-antibiotic anti-virulence therapies. The cytoplasmic membrane harbours lipoproteins which, when released, are highly proinflammatory.

This Research Topic will comprise only Reviews and Mini Reviews, reflecting the current state-of-the-art concerning surface proteins of Gram-positive bacterial pathogens.