Type III Secretion Injectosome and Effector Proteins.

Pertussis, also known as whooping cough, is a resurging acute respiratory disease of humans primarily caused by the Gram-negative coccobacilli , and less commonly by the human-adapted lineage of . The ovine-adapted lineage of infects only sheep, while causes chronic and often asymptomatic respiratory infections in a broad range of mammals but rarely in humans. A largely overlapping set of virulence factors inflicts the pathogenicity of these bordetellae. Their genomes also harbor a pathogenicity island, named locus, that encodes components of the type III secretion injectosome, and adjacent locus with the type III regulatory proteins. The Bsc injectosome of bordetellae translocates the cytotoxic BteA effector protein, also referred to as BopC, into the cells of the mammalian hosts. While the role of type III secretion activity in the persistent colonization of the lower respiratory tract by is well recognized, the functionality of the type III secretion injectosome in was overlooked for many years due to the adaptation of laboratory-passaged strains. This review highlights the current knowledge of the type III secretion system in the so-called classical species, comprising , and , and discusses its functional divergence. Comparison with other well-studied bacterial injectosomes, regulation of the type III secretion on the transcriptional and post-transcriptional level, and activities of BteA effector protein and BopN protein, homologous to the type III secretion gatekeepers, are addressed.