Clathrin adaptor proteins, also known as adaptins, are

vesicular transport adaptor protein Vesicular transport adaptor proteins are proteins involved in forming complexes that function in the trafficking of molecules from one subcellular location to another. These complexes concentrate the correct cargo molecules in vesicles that bud o ...

s associated with

clathrin Clathrin is a protein that plays a role in the formation of coated vesicles. Clathrin was first isolated by Barbara Pearse in 1976. It forms a triskelion shape composed of three clathrin heavy chains and three light chains. When the triskel ...

. The association between adaptins and clathrin are important for vesicular cargo selection and transporting. Clathrin coats contain both clathrin (acts as a scaffold) and adaptor complexes that link clathrin to receptors in coated

vesicles Vesicle may refer to: ; In cellular biology or chemistry * Vesicle (biology and chemistry), a supramolecular assembly of lipid molecules, like a cell membrane * Synaptic vesicle In a neuron, synaptic vesicles (or neurotransmitter vesicles) s ...

. Clathrin-associated protein complexes are believed to interact with the cytoplasmic tails of

membrane protein Membrane proteins are common proteins that are part of, or interact with, biological membranes. Membrane proteins fall into several broad categories depending on their location. Integral membrane proteins are a permanent part of a cell membrane ...

s, leading to their selection and concentration. Therefore, adaptor proteins are responsible for the recruitment of cargo molecules into a growing clathrin-coated pits. The two major types of clathrin adaptor complexes are the

heterotetramer A tetrameric protein is a protein with a quaternary structure of four subunits (tetrameric). Homotetramers have four identical subunits (such as glutathione S-transferase), and heterotetramers are complexes of different subunits. A tetrame ...

ic vesicular transport adaptor proteins (AP1-5), and the monomeric GGA (Golgi-localising, Gamma-adaptin ear homology, ARF-binding proteins) adaptors. Adaptins are distantly related to the other main type of vesicular transport proteins, the

coatomer The coatomer is a protein complex that coats membrane-bound transport vesicles. Two types of coatomers are known: *COPI (retrograde transport from trans-Golgi network to cis-Golgi network and endoplasmic reticulum) *COPII (anterograde transpo ...

subunits, sharing between 16% and 26% of their amino acid sequence. Adaptor protein (AP) complexes are found in coated vesicles and clathrin-coated pits. AP complexes connect cargo proteins and lipids to clathrin at vesicle budding sites, as well as binding accessory proteins that regulate coat assembly and disassembly (such as AP180,

epsin Epsins are a family of highly conserved membrane proteins that are important in creating membrane curvature. Epsins contribute to membrane deformations like endocytosis, and block vesicle formation during mitosis. Structure Epsin contains var ...

s and

auxilin Putative tyrosine-protein phosphatase auxilin is an enzyme that in humans is encoded by the ''DNAJC6'' gene. Function DNAJC6 belongs to the evolutionarily conserved DNAJ/HSP40 family of proteins, which regulate molecular chaperone activity by ...

). There are different AP complexes in mammals. AP1 is responsible for the transport of

lysosomal A lysosome () is a membrane-bound organelle that is found in all mammalian cells, with the exception of red blood cells (erythrocytes). There are normally hundreds of lysosomes in the cytosol, where they function as the cell’s degradation cent ...

hydrolase In biochemistry, hydrolases constitute a class of enzymes that commonly function as biochemical catalysts that use water to break a chemical bond: :\ce \quad \xrightarrowtext\quad \ce This typically results in dividing a larger molecule into s ...

s between the trans-Golgi network, and

endosome Endosomes are a collection of intracellular sorting organelles in eukaryotic cells. They are parts of the endocytic membrane transport pathway originating from the trans Golgi network. Molecules or ligands internalized from the plasma membra ...

AP2 adaptor complex The AP2 adaptor complex is a multimeric protein that works on the cell membrane to internalize cargo in clathrin-mediated endocytosis. It is a stable complex of four adaptins which give rise to a structure that has a core domain and two appendage d ...

associates with the plasma membrane and is responsible for

endocytosis Endocytosis is a cellular process in which Chemical substance, substances are brought into the cell. The material to be internalized is surrounded by an area of cell membrane, which then buds off inside the cell to form a Vesicle (biology and chem ...

. AP3 is responsible for protein trafficking to lysosomes and other related

organelle In cell biology, an organelle is a specialized subunit, usually within a cell (biology), cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as Organ (anatomy), organs are to th ...

s. AP4 is less well characterised. AP complexes are heterotetramers composed of two large subunits (adaptins), a medium subunit (mu) and a small subunit (sigma). For example, in AP1 these subunits are gamma-1-adaptin, beta-1-adaptin, mu-1 and sigma-1, while in AP2 they are alpha-adaptin, beta-2-adaptin, mu-2 and sigma-2. Each subunit has a specific function. Adaptins recognise and bind to clathrin through their hinge region (clathrin box), and recruit accessory proteins that modulate AP function through their C-terminal ear (appendage) domains. Mu recognises tyrosine-based sorting signals within the cytoplasmic domains of

transmembrane A transmembrane protein is a type of integral membrane protein that spans the entirety of the cell membrane. Many transmembrane proteins function as gateways to permit the transport of specific substances across the membrane. They frequently u ...

cargo proteins. One function of clathrin and AP2 complex-mediated endocytosis is to regulate the number of GABA_A receptors available at the cell surface .

References

External links

* * {{InterPro content, IPR008968 Peripheral membrane proteins Protein families

See also

References

External links