title: Excretion of cytosolic proteins (ECP) in bacteria.
abstract: Excretion of cytosolic proteins (ECP) has been reported in bacteria and eukaryotes. As none of the classical signal peptide (SP) dependent or SP-independent pathways could be associated with ECP, it has been also referred to as 'non-classical protein export'. When microbiologists first began to study this subject in 1990, mainly singular cytoplasmic proteins were investigated, such as GAPDH at the cell surface and in the supernatant of pathogenic streptococci or glutamine synthetase (GlnA) as a major extracellular protein in pathogenic mycobacteria. Later, with the rising popularity of proteomics, it became obvious that the secretome of most bacteria contained a copious amount of cytosolic proteins. In particular ancient proteins such as glycolytic enzymes, chaperones, translation factors or enzymes involved in detoxification of reactive oxygen were found in the supernatants. As the excreted proteins do not possess a common motive, the most widespread opinion is that ECP is due to cell lysis. Indeed, upregulation of autolysins or distortion of the murein structure increased ECP, suggesting that enhanced ECP is some sort of survival strategy to counteract osmotic stress. However, in the meantime there are mounting evidences and hints that speak against cell lysis as a primary mechanism for ECP. Very likely, ECP belongs to the normal life cycle of bacteria and involves a programmed process. This review provides a brief overview of the 'non-classical protein export'.
authors.affiliation: Microbial Genetics, Interfaculty Institute for Microbiology and Infection Medicine Tübingen (IMIT), University of Tübingen, 72076 Tübingen, Germany. Electronic address: friedrich.goetz@uni-tuebingen.de.
authors.forename: Friedrich
authors.initials: F
authors.lastname: Götz
authors.affiliation: Microbial Genetics, Interfaculty Institute for Microbiology and Infection Medicine Tübingen (IMIT), University of Tübingen, 72076 Tübingen, Germany.
authors.forename: Wenqi
authors.initials: W
authors.lastname: Yu
authors.affiliation: Microbial Genetics, Interfaculty Institute for Microbiology and Infection Medicine Tübingen (IMIT), University of Tübingen, 72076 Tübingen, Germany.
authors.forename: Linda
authors.initials: L
authors.lastname: Dube
authors.affiliation: Microbial Genetics, Interfaculty Institute for Microbiology and Infection Medicine Tübingen (IMIT), University of Tübingen, 72076 Tübingen, Germany.
authors.forename: Marcel
authors.initials: M
authors.lastname: Prax
authors.affiliation: Microbial Genetics, Interfaculty Institute for Microbiology and Infection Medicine Tübingen (IMIT), University of Tübingen, 72076 Tübingen, Germany.
authors.forename: Patrick
authors.initials: P
authors.lastname: Ebner
mesh_terms: D001419:Bacteria / Q000378:metabolism*; D001426:Bacterial Proteins / Q000378:metabolism*; D001433:Bacteriolysis; D021381:Protein Transport
chemical_list: D001426:Bacterial Proteins
keywords: Bacillus; Bacteria; Cytoplasmic membrane (CM); Excretion of cytosolic proteins (ECP); Secretome; Staphylococcus; Streptococcus