membrane trafficking


vesicle Vesicle may refer to: ; In cellular biology or chemistry * Vesicle (biology and chemistry) s in an aqueous An aqueous solution is a solution Image:SaltInWaterSolutionLiquid.jpg, Making a saline water solution by dissolving Salt, table salt ...
trafficking in
eukaryotic Eukaryotes () are organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy (biology), tax ...
animal cells involves movement of biochemical signal molecules from synthesis-and-packaging locations in the
Golgi body
Golgi body
to specific release locations on the inside of the plasma
membrane Image:Schematic size.jpg, up150px, Schematic of size-based membrane exclusion A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Biological membr ...
of the secretory cell. It takes place in the form of Golgi membrane-bound micro-sized vesicles, termed membrane vesicles (MVs). In this process, the packed cellular products are released or secreted outside the cell, across its
plasma membrane cell membrane vs. Prokaryotes A prokaryote () is a single-celled organism A unicellular organism, also known as a single-celled organism, is an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organ ...
. On the other hand, the vesicular membrane is retained and recycled by the secretory cells. This phenomenon has a major role in synaptic
neurotransmission 280px, The presynaptic neuron (top) releases a neurotransmitter, which activates receptors on the nearby postsynaptic cell (bottom). Neurotransmission (Latin: ''transmissio'' "passage, crossing" from ''transmittere'' "send, let through") is the pr ...
endocrine The endocrine system is a messenger system comprising feedback loops of the hormone A hormone (from the Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Re ...
mucous Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membrane A mucous membrane or mucosa is a membrane that lines various cavities in the body and covers the surface of internal organs. It consists of one or more layers ...
secretion, granular-product
secretionSecretion is the movement of material from one point to another, such as a secreted chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up sp ...
neutrophils Neutrophils (also known as neutrocytes or heterophils) are the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. They form an essential part of the innate immune system, with their functions varying in ...

, and other phenomena. The scientists behind this discovery were awarded
Nobel prize The Nobel Prizes ( ; sv, Nobelpriset ; no, Nobelprisen ) are five separate prizes that, according to Alfred Nobel's Will and testament, will of 1895, are awarded to "those who, during the preceding year, have conferred the greatest benefit to ...
for the year 2013. In
prokaryotic A prokaryote is a typically unicellular organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. It is a syn ...
gram-negative Gram-negative bacteria are bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few microm ...
bacterial cells, membrane vesicle trafficking is mediated through bacterial outer membrane bounded nano-sized vesicles, called
bacterial outer membrane vesicles Bacterial outer membrane vesicles (OMVs) are vesicles of lipids In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biol ...
(OMVs). In this case, however, the OMV membrane is secreted as well, along with OMV-contents to outside the secretion-active
bacterium Bacteria (; common noun bacteria, singular bacterium) are a type of biological cell The cell (from Latin ''cella'', meaning "small room") is the basic structural, functional, and biological unit of all known organisms. Cells are the sma ...
. This different phenomenon has a maor role in host-pathogen interactions, endotoxic shock in patients, invasion and infection of animals or plants, inter-species bacterial competition, quorum sensing, exocytosis, and other areas.

Movement within eukaryotic cells

Once vesicles are produced in the endoplasmic reticulum and modified in the Golgi apparatus, golgi body they make their way to a variety of destinations within the cell. Vesicles first leave the golgi body and are released into the cytoplasm in a process called budding. Vesicles are then moved towards their destination by Motor protein, motor proteins. Once the vesicle arrives at its destination it joins with the bi-lipid layer in a process called Lipid bilayer fusion, fusion, and then releases its contents.


Receptors embedded in the membrane of the golgi body bind specific cargo (such as dopamine) on the lumenal side of the vesicle. These cargo receptors then recruit a variety of proteins including other cargo receptors and Coatomer, coat proteins such as clathrin, COPI and COPII. As more and more of these coating proteins come together, they cause the vesicle to bud outward and eventually break free into the cytoplasm. The coating proteins are then shed into the cytoplasm to be recycled and reused.

Motility between cell compartments

For movement between different compartments within the cell, vesicles rely on the motor proteins myosin, kinesin (primarily anterograde transport) and dynein (primarily retrograde transport). One end of the motor proteins attaches to the vesicle while the other end attaches to either Microtubule, microtubules or Microfilament, microfilaments. The motor proteins then move by hydrolyzing ATP, which propels the vesicle towards its destination.

Docking and Fusion

As a vesicle nears its intended location, Rab (G-protein), RAB proteins in the vesicle membrane interact with docking proteins at the destination site. These docking proteins bring the vesicle in closer to interact with the SNARE (protein), SNARE Complex found in the target membrane. The SNARE complex reacts with synaptobrevin found on the vesicle membrane. This forces the vesicle membrane against the membrane of the target complex (or the outer membrane of the cell) and causes the two membranes to fuse. Depending on whether the vesicle fuses with a target complex or the outer membrane, the contents of the vesicle are then released either into the target complex or outside the cell.

Examples In eukaryotes

# ''Intracellular'' trafficking occurs between subcellular compartments like Golgi cisternae and multivesicular endosomes for transport of soluble proteins as MVs. # ''Budding'' of MVs directly from plasma membrane as ''microvesicles'' released outside the secretory cell (biology), cells. # ''Exosomes'' are MVs that can form inside an internal compartment like multivesicular endosome. Exosomes are released eventually due to fusion of this endosome with plasma membrane of cell. # ''Hijacking'' of exosomal machinery by some viruses like retroviruses, wherein viruses bud inside multivesicular endosomes and get secreted subsequently as exosomes. All these types (1-4) of modes of membrane vesicle trafficking, taking place in eukaryotic cells have been explained diagrammatically.

In prokaryotes

Unlike in eukaryotes, membrane vesicular trafficking in prokaryotes is an emerging area in interactive biology for intra-species (quorum sensing) and inter-species signaling at host-pathogen interface, as prokaryotes lack internal membrane-compartmentalization of their cytoplasm. Bacterial membrane vesicles dispersion along the cell surface was measured in live ''Escherichia coli'', commensal bacteria common in the human gut. Antibiotic treatment altered vesicle dynamics, vesicle-to-membrane affinity, and surface properties of the cell membranes, generally enhancing vesicle transport along the surfaces of bacterial membranes and suggesting that their motion properties could be a signature of antibiotic stress. For more than four decades, cultures of gram negative microbes revealed the presence of nanoscale membrane vesicles. A role for membrane vesicles in pathogenic processes has been suspected since the 1970s, when they were observed in gingival plaque by electron microscopy. These vesicles were suspected to promote bacterial adhesion to the host epithelial cell surface. Their role in invasion of animal host cells ''in vivo'' was then demonstrated. In inter-bacterial interactions, OMVs released by ''Pseudomonas aeruginosa'' microbes were shown to fuse with outer membrane of other gram negative microbes causing their bacteriolysis; these OMVs could lyse gram-positive microbes as well. Role of OMVs in ''Helicobacter pylori'' infection of ''human'' primary antral epithelial cells, as model that closely resembles human stomach, has also been confirmed VacA-containing OMVs could also be detected in human gastric mucosa, infected with ''H. pylori.''. ''Salmonella'' OMVs were also shown to have direct role in invasion of chicken ileal epithelial cells ''in vivo'' in the year, 1993 (ref 4) and later, in hijacking of defense macrophages into sub-service for pathogen replication and consequent apoptosis of infected macrophages in typhoid-like animal infection. These studies brought the focus on OMVs into ''membrane vesicle trafficking'' and showed this phenomenon as involved in multifarious processes like genetic transformation, quorum sensing, competition arsenal among microbes, etc., and invasion, infection, immuno-modulation, etc., of animal hosts. A mechanism has already been proposed for generation of OMVs by gram negative microbes involving, expansion of pockets of periplasm (named, ''periplasmic organelles'') due to accumulation of bacterial cell secretions and their pinching off as outer membrane bounded vesicles (OMVs) on the lines of a 'soap bubble' formation with a bubble tube, and further fusion or uptake of diffusing OMVs by host/target cells (Fig. 2). In conclusion, ''membrane vesicle trafficking'' via OMVs of Gram-negative organisms, cuts across species and kingdoms - including plant kingdom{{cite journal , vauthors = Bahar O, Pruitt R, Luu DD, Schwessinger B, Daudi A, Liu F, Ruan R, Fontaine-Bodin L, Koebnik R, Ronald P , title = The Xanthomonas Ax21 protein is processed by the general secretory system and is secreted in association with outer membrane vesicles , journal = PeerJ , volume = 2 , pages = e242 , date = 2014 , pmid = 24482761 , pmc = 3897388 , doi = 10.7717/peerj.242 - in the realm of cell-to-cell signaling.

See also

*Bacterial outer membrane vesicles *Endocytosis *Exocytosis *Host-pathogen interaction *Secretory pathway *Vesicle (Biology and Chemistry) *Virulence


External links

*Nobel Prize of year 2013 in Physiology and Medicine - press release *Discovery of vesicular exocytosis in prokaryotes Membrane biology