Bacterial secretion systems are protein complexes present on the cell membranes of bacteria for secretion of substances. Specifically, they are the cellular devices used by pathogenic bacteria to secrete their virulence factors (mainly of proteins) to invade the host cells. They can be classified into different types based on their specific structure, composition and activity. Generally, proteins can be secreted through two different processes. One process is a one-step mechanism in which proteins from the cytoplasm of bacteria are transported and delivered directly through the cell membrane into the host cell. Another involves a two-step activity in which the proteins are first transported out of the inner cell membrane, then deposited in the periplasm, and finally through the outer cell membrane into the host cell. Type IX secretion systems (T9SS) are found regularly in the Fibrobacteres-Chlorobi-Bacteroidetes lineage of bacteria, where member species include an outer membrane. The system is involved variably in one type of gliding motility, in the proper targeting of certain virulence factors to the cell surface, and the degradation of complex of biopolymers. T9SS has also been known as Por (porphyrin accumulation on the cell surface) secretion, after the oral pathogen Porphyromonas gingivalis. At least sixteen structural components of the system have been described, including PorU, a protein-sorting transpeptidase that removes the C-terminal sorting signal from cargo proteins and mediates their attachment instead to lipopolysaccharide. Here you can see a recent cryoEM structure Type 9 secretion system extended translocon - SprA-PorV-PPI-RemZ-SkpA-SprE complex from Flavobacterium johnsoniae (PDB code: 8GL8)

#molecularart ... #bacteria ... #transporter ... #translocon ... #type9 ... #cryoem

Structure rendered with @proteinimaging and depicted with @corelphotopaint