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Secretion is the movement of material from one point to another, such as a secreted
chemical substance
A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., w ...
from a
cell
Cell most often refers to:
* Cell (biology), the functional basic unit of life
Cell may also refer to:
Locations
* Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery ...
or
gland. In contrast,
excretion
Excretion is a process in which metabolic waste
is eliminated from an organism. In vertebrates this is primarily carried out by the lungs, kidneys, and skin. This is in contrast with secretion, where the substance may have specific tasks after ...
is the removal of certain substances or waste products from a cell or organism. The classical mechanism of cell secretion is via secretory portals at the
plasma membrane called
porosomes.
Porosomes are permanent cup-shaped
lipoprotein
A lipoprotein is a biochemical assembly whose primary function is to transport hydrophobic lipid (also known as fat) molecules in water, as in blood plasma or other extracellular fluids. They consist of a triglyceride and cholesterol center, su ...
structures embedded in the cell membrane, where secretory vesicles transiently dock and fuse to release intra-vesicular contents from the cell.
Secretion in bacterial species means the transport or translocation of effector molecules for example:
proteins,
enzymes or
toxin
A toxin is a naturally occurring organic poison produced by metabolic activities of living cells or organisms. Toxins occur especially as a protein or conjugated protein. The term toxin was first used by organic chemist Ludwig Brieger (1849 ...
s (such as
cholera toxin
Cholera toxin (also known as choleragen and sometimes abbreviated to CTX, Ctx or CT) is AB5 multimeric protein complex secreted by the bacterium ''Vibrio cholerae''. CTX is responsible for the massive, watery diarrhea characteristic of cholera i ...
in
pathogenic bacteria e.g. ''
Vibrio cholerae
''Vibrio cholerae'' is a species of Gram-negative, facultative anaerobe and comma-shaped bacteria. The bacteria naturally live in brackish or saltwater where they attach themselves easily to the chitin-containing shells of crabs, shrimps, and oth ...
'') from across the interior (
cytoplasm
In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. ...
or
cytosol
The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells ( intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondri ...
) of a bacterial cell to its exterior. Secretion is a very important mechanism in bacterial functioning and operation in their natural surrounding environment for adaptation and survival.
In eukaryotic cells
Mechanism
Eukaryotic
Eukaryotes () are organisms whose Cell (biology), cells have a cell nucleus, nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the ...
cells, including
human cells, have a highly
evolved
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
process of secretion. Proteins
targeted for the outside are
synthesized by
ribosomes docked to the rough
endoplasmic reticulum (ER). As they are synthesized, these proteins translocate into the ER
lumen, where they are
glycosylated
Glycosylation is the reaction in which a carbohydrate (or ' glycan'), i.e. a glycosyl donor, is attached to a hydroxyl or other functional group of another molecule (a glycosyl acceptor) in order to form a glycoconjugate. In biology (but not ...
and where molecular
chaperones aid
protein folding
Protein folding is the physical process by which a protein chain is translated to its native three-dimensional structure, typically a "folded" conformation by which the protein becomes biologically functional. Via an expeditious and reproduc ...
.
Misfolded proteins
Protein folding is the physical process by which a protein chain is translated to its native three-dimensional structure, typically a "folded" conformation by which the protein becomes biologically functional. Via an expeditious and reproduci ...
are usually identified here and retrotranslocated by
ER-associated degradation to the
cytosol
The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells ( intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondri ...
, where they are degraded by a
proteasome. The
vesicle
Vesicle may refer to:
; In cellular biology or chemistry
* Vesicle (biology and chemistry)
In cell biology, a vesicle is a structure within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer. Vesicles form nat ...
s containing the properly folded proteins then enter the
Golgi apparatus
The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. Part of the endomembrane system in the cytoplasm, it packages proteins into membrane-bound vesicles ...
.
In the Golgi apparatus, the glycosylation of the proteins is modified and further
post-translational modification
Post-translational modification (PTM) is the covalent and generally enzymatic modification of proteins following protein biosynthesis. This process occurs in the endoplasmic reticulum and the golgi apparatus. Proteins are synthesized by ribos ...
s, including cleavage and functionalization, may occur. The
proteins are then moved into secretory vesicles which travel along the
cytoskeleton
The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including those of bacteria and archaea. In eukaryotes, it extends from the cell nucleus to the cell membrane and is com ...
to the edge of the cell. More modification can occur in the secretory vesicles (for example
insulin is cleaved from
proinsulin
Proinsulin is the prohormone precursor to insulin made in the beta cells of the islets of Langerhans, specialized regions of the pancreas. In humans, proinsulin is encoded by the ''INS'' gene. The islets of Langerhans only secrete between 1% and ...
in the secretory vesicles).
Eventually, there is
vesicle fusion Vesicle fusion is the merging of a vesicle with other vesicles or a part of a cell membrane. In the latter case, it is the end stage of secretion from secretory vesicles, where their contents are expelled from the cell through exocytosis. Vesicles c ...
with the
cell membrane
The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment ( ...
at porosomes, by a process called
exocytosis, dumping its contents out of the cell's environment.
Strict
biochemical control is maintained over this sequence by usage of a
pH gradient: the pH of the cytosol is 7.4, the ER's pH is 7.0, and the cis-golgi has a pH of 6.5. Secretory vesicles have pHs ranging between 5.0 and 6.0; some secretory vesicles evolve into
lysosome
A lysosome () is a membrane-bound organelle found in many animal cells. They are spherical vesicles that contain hydrolytic enzymes that can break down many kinds of biomolecules. A lysosome has a specific composition, of both its membrane pr ...
s, which have a pH of 4.8.
Nonclassical secretion
There are many proteins like
FGF1
Fibroblast growth factor 1, (FGF-1) also known as acidic fibroblast growth factor (aFGF), is a growth factor and signaling protein encoded by the ''FGF1'' gene. It is synthesized as a 155 amino acid polypeptide, whose mature form is a non-glycos ...
(aFGF),
FGF2
Fibroblast growth factor 2, also known as basic fibroblast growth factor (bFGF) and FGF-β, is a growth factor and signaling protein encoded by the ''FGF2'' gene. It binds to and exerts effects via specific fibroblast growth factor receptor ''(FG ...
(bFGF),
interleukin-1
The Interleukin-1 family (IL-1 family) is a group of 11 cytokines that plays a central role in the regulation of immune and inflammatory responses to infections or sterile insults.
Discovery
Discovery of these cytokines began with studies on t ...
(IL1) etc. which do not have a signal sequence. They do not use the classical ER-Golgi pathway. These are secreted through various nonclassical pathways.
At least four nonclassical (unconventional) protein secretion pathways have been described. They include:
* direct protein translocation across the plasma membrane likely through
membrane transport protein
A membrane transport protein (or simply transporter) is a membrane protein involved in the movement of ions, small molecules, and macromolecules, such as another protein, across a biological membrane. Transport proteins are integral transmembra ...
s
*
blebbing
In cell biology, a bleb is a bulge of the plasma membrane of a cell, characterized by a spherical, bulky morphology. It is characterized by the decoupling of the cytoskeleton from the plasma membrane, degrading the internal structure of the cell, ...
* lysosomal secretion
* release via exosomes derived from multivesicular bodies
In addition, proteins can be released from cells by mechanical or physiological wounding and through non-lethal, transient
oncotic pores in the plasma membrane induced by washing cells with serum-free media or buffers.
In human tissues
Many
human cell types
There are many different types of cell (biology), cells in the human body.
Cells derived primarily from endoderm
Exocrine secretory epithelial cells
*Brunner's gland cell in duodenum (enzymes and alkaline mucus)
*Insulated goblet cell of re ...
have the ability to be secretory cells. They have a well-developed
endoplasmic reticulum, and
Golgi apparatus
The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. Part of the endomembrane system in the cytoplasm, it packages proteins into membrane-bound vesicles ...
to fulfill this function.
Tissues that produce secretions include the
gastrointestinal tract which secretes
digestive enzyme
Digestive enzymes are a group of enzymes that break down polymeric macromolecules into their smaller building blocks, in order to facilitate their absorption into the cells of the body. Digestive enzymes are found in the digestive tracts of anima ...
s and
gastric acid, the
lungs which secrete
surfactants, and
sebaceous gland
A sebaceous gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in the greatest nu ...
s which secrete
sebum
A sebaceous gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in the greatest nu ...
to lubricate the skin and hair.
Meibomian gland
Meibomian glands (also called tarsal glands, palpebral glands, and tarsoconjunctival glands) are sebaceous glands along the rims of the eyelid inside the tarsal plate. They produce meibum, an oily substance that prevents evaporation of the eye ...
s in the
eyelid
An eyelid is a thin fold of skin that covers and protects an eye. The levator palpebrae superioris muscle retracts the eyelid, exposing the cornea to the outside, giving vision. This can be either voluntarily or involuntarily. The human eye ...
secrete
meibum
Meibomian glands (also called tarsal glands, palpebral glands, and tarsoconjunctival glands) are sebaceous glands along the rims of the eyelid inside the tarsal plate. They produce meibum, an oily substance that prevents evaporation of the eye' ...
to lubricate and protect the eye.
In gram-negative bacteria
Secretion is not unique to eukaryotes - it is also present in bacteria and archaea as well.
ATP binding cassette
The ATP-binding cassette transporters (ABC transporters) are a transport system superfamily that is one of the largest and possibly one of the oldest gene families. It is represented in all extant phyla, from prokaryotes to humans. ABC transpo ...
(ABC) type transporters are common to the three domains of life. Some secreted proteins are translocated across the cytoplasmic membrane by the
SecYEG translocon The translocon (also known as a translocator or translocation channel) is a complex of proteins associated with the translocation of polypeptides across membranes. In eukaryotes the term translocon most commonly refers to the complex that transport ...
, one of two translocation systems, which requires the presence of an N-terminal signal peptide on the secreted protein. Others are translocated across the cytoplasmic membrane by the
twin-arginine translocation pathway
The twin-arginine translocation pathway (Tat pathway) is a protein export, or secretion pathway found in plants, bacteria, and archaea. In contrast to the Sec pathway which transports proteins in an unfolded manner, the Tat pathway serves to ac ...
(Tat).
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 ...
have two membranes, thus making secretion topologically more complex. There are at least six specialized secretion systems in gram-negative bacteria. Many secreted proteins are particularly important in bacterial pathogenesis.
Type I secretion system (T1SS or TOSS)
Type I secretion is a chaperone dependent secretion system employing the Hly and Tol gene clusters. The process begins as a leader sequence on the protein to be secreted is recognized by HlyA and binds HlyB on the membrane. This signal sequence is extremely specific for the ABC transporter. The HlyAB complex stimulates HlyD which begins to uncoil and reaches the outer membrane where TolC recognizes a terminal molecule or signal on HlyD. HlyD recruits TolC to the inner membrane and HlyA is excreted outside of the outer membrane via a long-tunnel protein channel.
Type I secretion system transports various molecules, from ions, drugs, to proteins of various sizes (20 – 900 kDa). The molecules secreted vary in size from the small ''
Escherichia coli
''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Esc ...
'' peptide colicin V, (10 kDa) to the ''
Pseudomonas fluorescens'' cell adhesion protein LapA of 520 kDa. The best characterized are the
RTX toxin
The RTX toxin superfamily is a group of cytolysins and cytotoxins produced by bacteria. There are over 1000 known members with a variety of functions. The RTX family is defined by two common features: characteristic repeats in the toxin protein se ...
s and the lipases. Type I secretion is also involved in export of non-proteinaceous substrates like cyclic β-glucans and polysaccharides.
Type II secretion system (T2SS)
Proteins secreted through the type II system, or main terminal branch of the general secretory pathway, depend on the Sec or Tat system for initial transport into 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 ...
. Once there, they pass through the outer membrane via a multimeric (12–14 subunits) complex of pore forming secretin proteins. In addition to the secretin protein, 10–15 other inner and outer membrane proteins compose the full secretion apparatus, many with as yet unknown function. Gram-negative
type IV pili
A pilus (Latin for 'hair'; plural: ''pili'') is a hair-like appendage found on the surface of many bacteria and archaea. The terms ''pilus'' and '' fimbria'' (Latin for 'fringe'; plural: ''fimbriae'') can be used interchangeably, although some r ...
use a modified version of the type II system for their biogenesis, and in some cases certain proteins are shared between a pilus complex and type II system within a single bacterial species.
Type III secretion system (T3SS or TTSS)
It is homologous to the basal body in bacterial flagella. It is like a molecular syringe through which a bacterium (e.g. certain types of ''
Salmonella'', ''
Shigella
''Shigella'' is a genus of bacteria that is Gram-negative, facultative anaerobic, non-spore-forming, nonmotile, rod-shaped, and genetically closely related to '' E. coli''. The genus is named after Kiyoshi Shiga, who first discovered it in 1 ...
'', ''
Yersinia
''Yersinia'' is a genus of bacteria in the family Yersiniaceae. ''Yersinia'' species are Gram-negative, coccobacilli bacteria, a few micrometers long and fractions of a micrometer in diameter, and are facultative anaerobes. Some members of ''Yer ...
'', ''
Vibrio
''Vibrio'' is a genus of Gram-negative bacteria, possessing a curved-rod (comma) shape, several species of which can cause foodborne infection, usually associated with eating undercooked seafood. Being highly salt tolerant and unable to survive ...
'') can inject proteins into eukaryotic cells. The low Ca
2+ concentration in the cytosol opens the gate that regulates T3SS. One such mechanism to detect low calcium concentration has been illustrated by the lcrV (Low Calcium Response) antigen utilized by ''
Yersinia pestis
''Yersinia pestis'' (''Y. pestis''; formerly '' Pasteurella pestis'') is a gram-negative, non-motile, coccobacillus bacterium without spores that is related to both ''Yersinia pseudotuberculosis'' and ''Yersinia enterocolitica''. It is a facult ...
'', which is used to detect low calcium concentrations and elicits T3SS attachment. The Hrp system in plant pathogens inject harpins and pathogen effector proteins through similar mechanisms into plants. This secretion system was first discovered in ''
Yersinia pestis
''Yersinia pestis'' (''Y. pestis''; formerly '' Pasteurella pestis'') is a gram-negative, non-motile, coccobacillus bacterium without spores that is related to both ''Yersinia pseudotuberculosis'' and ''Yersinia enterocolitica''. It is a facult ...
'' and showed that toxins could be injected directly from the bacterial cytoplasm into the cytoplasm of its host's cells rather than simply be secreted into the extracellular medium.
Type IV secretion system (T4SS or TFSS)
It is homologous to
conjugation machinery of bacteria, the
conjugative pili. It is capable of transporting both DNA and proteins. It was discovered in ''Agrobacterium tumefaciens'', which uses this system to introduce the T-DNA portion of the Ti plasmid into the plant host, which in turn causes the affected area to develop into a crown gall (tumor). ''
Helicobacter pylori
''Helicobacter pylori'', previously known as ''Campylobacter pylori'', is a gram-negative, microaerophilic, spiral (helical) bacterium usually found in the stomach. Its helical shape (from which the genus name, helicobacter, derives) is thoug ...
'' uses a type IV secretion system to deliver
CagA
''Helicobacter pylori'' virulence factor CagA (cytotoxin-associated gene A) is a 120–145kDa protein encoded on the 40kb ''cag'' pathogenicity island (PAI). ''H. pylori'' strains can be divided into CagA positive or negative strains. Approximately ...
into gastric epithelial cells, which is associated with gastric carcinogenesis.
''
Bordetella pertussis
''Bordetella pertussis'' is a Gram-negative, aerobic, pathogenic, encapsulated coccobacillus of the genus ''Bordetella'', and the causative agent of pertussis or whooping cough. Like '' B. bronchiseptica'', ''B. pertussis'' is motile and expre ...
'', the causative agent of whooping cough, secretes the
pertussis toxin
Pertussis toxin (PT) is a protein-based AB5-type exotoxin produced by the bacterium ''Bordetella pertussis'', which causes whooping cough. PT is involved in the colonization of the respiratory tract and the establishment of infection. Rese ...
partly through the type IV system. ''
Legionella pneumophila'', the causing agent of legionellosis (Legionnaires' disease) utilizes a
type IVB secretion system, known as the icm/dot (intracellular multiplication / defect in organelle trafficking genes) system, to translocate numerous
effector proteins into its eukaryotic host.
The prototypic Type IVA secretion system is the VirB complex of ''
Agrobacterium tumefaciens''.
Protein members of this family are components of the type IV secretion system. They mediate
intracellular
This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...
transfer of
macromolecules via a
mechanism
Mechanism may refer to:
* Mechanism (engineering), rigid bodies connected by joints in order to accomplish a desired force and/or motion transmission
*Mechanism (biology), explaining how a feature is created
*Mechanism (philosophy), a theory that ...
ancestrally related to that of
bacterial conjugation machineries.
Function
In short, Type IV secretion system (T4SS), is the general mechanism by which bacterial cells secrete or take up macromolecules. Their precise mechanism remains unknown. T4SS is encoded on
Gram-negative
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 wa ...
conjugative elements in
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
.T4SS are cell envelope-spanning complexes or in other words 11–13 core proteins that form a channel through which DNA and proteins can travel from the cytoplasm of the donor cell to the cytoplasm of the recipient cell. Additionally, T4SS also secrete
virulence
Virulence is a pathogen's or microorganism's ability to cause damage to a host.
In most, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its ability to ...
factor proteins directly into host cells as well as taking up DNA from the medium during natural
transformation
Transformation may refer to:
Science and mathematics
In biology and medicine
* Metamorphosis, the biological process of changing physical form after birth or hatching
* Malignant transformation, the process of cells becoming cancerous
* Tran ...
, which shows the versatility of this macromolecular secretion apparatus.
Structure
As shown in the above figure, TraC, in particular consists of a three helix bundle and a loose globular appendage.
Interactions
T4SS has two effector proteins: firstly, ATS-1, which stands for Anaplasma translocated substrate 1, and secondly
AnkA, which stands for ankyrin repeat domain-containing protein A. Additionally, T4SS coupling proteins are VirD4, which bind to VirE2.
Type V secretion system (T5SS)
Also called the autotransporter system,
type V secretion involves use of the ''Sec'' system for crossing the inner membrane. Proteins which use this pathway have the capability to form 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 ...
with their C-terminus which inserts into the outer membrane, allowing the rest of the peptide (the passenger domain) to reach the outside of the cell. Often, autotransporters are cleaved, leaving the beta-barrel domain in the outer membrane and freeing the passenger domain. Some researchers believe remnants of the autotransporters gave rise to the
porins which form similar beta-barrel structures. A common example of an autotransporter that uses this secretion system is the
Trimeric Autotransporter Adhesins.
Type VI secretion system (T6SS)
Type VI secretion systems were originally identified in 2006 by the group of
John Mekalanos at the Harvard Medical School (Boston, USA) in two bacterial pathogens, ''
Vibrio cholerae
''Vibrio cholerae'' is a species of Gram-negative, facultative anaerobe and comma-shaped bacteria. The bacteria naturally live in brackish or saltwater where they attach themselves easily to the chitin-containing shells of crabs, shrimps, and oth ...
'' and ''
Pseudomonas aeruginosa
''Pseudomonas aeruginosa'' is a common encapsulated, gram-negative, aerobic–facultatively anaerobic, rod-shaped bacterium that can cause disease in plants and animals, including humans. A species of considerable medical importance, ''P. aerug ...
''.
These were identified when mutations in the Hcp and VrgG genes in ''Vibrio Cholerae'' led to decreased virulence and pathogenicity. Since then, Type VI secretion systems have been found in a quarter of all proteobacterial genomes, including animal, plant, human pathogens, as well as soil, environmental or marine bacteria.
While most of the early studies of Type VI secretion focused on its role in the pathogenesis of higher organisms, more recent studies suggested a broader physiological role in defense against simple eukaryotic predators and its role in inter-bacteria interactions.
The Type VI secretion system gene clusters contain from 15 to more than 20 genes, two of which, Hcp and VgrG, have been shown to be nearly universally secreted substrates of the system. Structural analysis of these and other proteins in this system bear a striking resemblance to the tail spike of the T4 phage, and the activity of the system is thought to functionally resemble phage infection.
Release of outer membrane vesicles
In addition to the use of the multiprotein complexes listed above, Gram-negative bacteria possess another method for release of material: the formation of
bacterial outer membrane vesicles. Portions of the outer membrane pinch off, forming nano-scale spherical structures made of a lipopolysaccharide-rich lipid bilayer enclosing periplasmic materials, and are deployed for
membrane vesicle trafficking Membrane vesicle trafficking in eukaryotic animal cells involves movement of biochemical signal molecules from synthesis-and-packaging locations in the Golgi body to specific release locations on the inside of the plasma membrane of the secretory ...
to manipulate environment or invade at
host-pathogen interface. Vesicles from a number of bacterial species have been found to contain virulence factors, some have immunomodulatory effects, and some can directly adhere to and intoxicate host cells. release of vesicles has been demonstrated as a general response to stress conditions, the process of loading cargo proteins seems to be selective.
Secretion in gram-positive bacteria
In some ''Staphylococcus'' and ''Streptococcus'' species, the accessory secretory system handles the export of highly repetitive adhesion glycoproteins.
See also
*
Bacterial effector protein Bacterial effectors are proteins secreted by pathogenic bacteria into the cells of their host, usually using a type 3 secretion system (TTSS/T3SS), a type 4 secretion system (TFSS/T4SS) or a Type VI secretion system (T6SS). Some bacteria inject on ...
*
Bacterial outer membrane vesicles
*
Host-pathogen interface
*
Membrane vesicle trafficking Membrane vesicle trafficking in eukaryotic animal cells involves movement of biochemical signal molecules from synthesis-and-packaging locations in the Golgi body to specific release locations on the inside of the plasma membrane of the secretory ...
*
Secretomics Secretomics is a type of proteomics which involves the analysis of the secretome—all the secreted proteins of a cell, tissue or organism. Secreted proteins are involved in a variety of physiological processes, including cell signaling and matrix ...
*
Secretory protein
A secretory protein is any protein, whether it be endocrine or exocrine, which is secreted by a cell. Secretory proteins include many hormones, enzymes, toxins, and antimicrobial peptides.
Secretory proteins are synthesized in the endoplasmic ret ...
s
*
Secretor status
References
[Z. Esna Ashari, N. Dasgupta, K. Brayton & S. Broschat, ]
An optimal set of features for predicting type IV secretion system effector proteins for a subset of species based on a multi-level feature selection approach
, PLOS ONE Journal, 2018, 13, e0197041. (doi.org/10.1371/journal.pone.0197041.)
Further reading
*
*
*
External links
*
* T5SS / Autotransporter illustration at
{{Authority control
Biochemistry
Cell biology
Physiology
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