The Type V secretion system was first described twenty years ago. Since then, much work has be done to elucidate functional aspects of members of this family and their mechanisms of biogenesis. What was once considered to be a quirky one-off system, with the discovery of the IgA1 protease secretion system of Neisseria gonorrhoeae, has been revealed as the largest family of secreted proteins amongst the Gram-negative bacteria.

The type V secretion system (T5SS) is comparatively is less complex than types I to IV. This secretion mechanism has been subdivided into sub-types (a), (b) and (c), as variations upon a theme were discovered. Each polypeptide secreted via the T5SS contains an N-terminal Sec-dependant signal sequence required to direct inner membrane export. The significant functional domain classifying molecules into these secretion systems is the dedicated outer membrane (outer membrane) β-barrel protein domain, through which secretion of the effector molecule is achieved.

from Scott-Tucker and Henderson in Bacterial Secreted Proteins

Further reading:

1. Bacterial Secreted Proteins: Secretory Mechanisms and Role in Pathogenesis
2. Microbiology Books

Labels: bacteria, protein, protein secretion, proteins