molecular biology Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including biomolecular synthesis, modification, mechanisms, and interactions. The study of chemical and physi ...

, an autotransporter domain is a

structural domain In molecular biology, a protein domain is a region of a protein's polypeptide chain that is self-stabilizing and that folds independently from the rest. Each domain forms a compact folded three-dimensional structure. Many proteins consist of s ...

found in some

bacterial outer membrane The bacterial outer membrane is found in gram-negative bacteria. Its composition is distinct from that of the inner cytoplasmic cell membrane - among other things, the outer leaflet of the outer membrane of many gram-negative bacteria includes ...

proteins. The domain is always located at the

C-terminal The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal tail, C-terminal end, or COOH-terminus) is the end of an amino acid chain (protein or polypeptide), terminated by a free carboxyl group (-COOH). When the protein is ...

end of the protein and forms a

beta-barrel In protein structures, a beta barrel is a beta sheet composed of tandem repeats that twists and coils to form a closed toroidal structure in which the first strand is bonded to the last strand (hydrogen bond). Beta-strands in many beta-barrels are ...

structure. The barrel is oriented in the membrane such that the N-terminal portion of the protein, termed the passenger domain, is presented on the cell surface. These proteins are typically

virulence factors Virulence factors (preferably known as pathogenicity factors or effectors in plant science) are cellular structures, molecules and regulatory systems that enable microbial pathogens (bacteria, viruses, fungi, and protozoa) to achieve the followin ...

, associated with infection or virulence in pathogenic bacteria. The name autotransporter derives from an initial understanding that the protein was self-sufficient in transporting the passenger domain through the outermembrane. This view has since been challenged by Benz and Schmidt. Secretion of polypeptide chains through the outer membrane of

Gram-negative bacteria Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...

can occur via a number of different pathways. The type V(a), or autotransporter, secretion pathway constitutes the largest number of secreted virulence factors of any one of the seven known types of secretion in Gram-negative bacteria. This secretion pathway is exemplified by the prototypical IgA1 Protease of ''Neisseria gonorrhoeae''. The protein is directed to the inner membrane by a signal peptide transported across the inner membrane via the Sec machinery. Once in the

periplasm The periplasm is a concentrated gel-like matrix in the space between the inner cytoplasmic membrane and the bacterial outer membrane called the ''periplasmic space'' in gram-negative bacteria. Using cryo-electron microscopy it has been found that ...

, the autotransporter domain inserts into the outer membrane. The passenger domain is passed through the center of the autotransporter domain to be presented on the outside of the cell, however the mechanism by which this occurs remains unclear. The C-terminal translocator domain corresponds to an outer membrane beta-barrel domain. The N-terminal passenger domain is translocated across the membrane, and may or may not be cleaved from the translocator domain. In those proteins where the cleavage is auto-catalytic, the peptidase domains belong to

MEROPS MEROPS is an online database for peptidases (also known as proteases, proteinases and proteolytic enzymes) and their inhibitors. The classification scheme for peptidases was published by Rawlings & Barrett in 1993, and that for protein inhibit ...

peptidase families S6 and S8. Passenger domains structurally characterized to date have been shown to be dominated by a protein fold known as a

beta helix A beta helix is a tandem protein repeat structure formed by the association of parallel beta strands in a helical pattern with either two or three faces. The beta helix is a type of solenoid protein domain. The structure is stabilized by inter- ...

, typified by

pertactin In molecular biology, pertactin (PRN) is a highly immunogenic virulence factor of ''Bordetella pertussis'', the bacterium that causes pertussis. Specifically, it is an outer membrane protein that promotes adhesion to tracheal epithelial cells. ...

. The folding of this domain is thought to be intrinsically linked to its method of outer membrane translocation.

See also

References

Further reading