membrane coat

Definition

Target type: cellularcomponent

Any of several different proteinaceous coats that can associate with membranes. Membrane coats include those formed by clathrin plus an adaptor complex, the COPI and COPII complexes, and possibly others. They are found associated with membranes on many vesicles as well as other membrane features such as pits and perhaps tubules. [GOC:mah]

Membrane coats are specialized protein structures that assemble on the cytoplasmic face of cellular membranes. These coats serve as platforms for the recruitment and sorting of specific cargo molecules, playing crucial roles in various cellular processes, including endocytosis, exocytosis, and vesicle trafficking. The key components of membrane coats include:

1. **Coat Proteins:** These proteins are the building blocks of the coat structure. They typically have a characteristic domain structure, including a cargo-binding domain and a self-association domain. Examples include clathrin, COPI, COPII, and retromer.
2. **Adaptor Proteins:** These proteins act as intermediaries between cargo molecules and coat proteins. They possess specific binding sites for both cargo and coat components, ensuring the selective packaging of cargo into coated vesicles. Examples include AP1, AP2, and GGAs.
3. **Regulatory Proteins:** These proteins regulate the assembly and disassembly of coat structures. They can interact with coat proteins, adaptor proteins, or other cellular factors to control the timing and location of coat formation. Examples include dynamin and BAR domain proteins.

The specific composition and organization of the coat can vary depending on the type of membrane and the cellular process involved. For instance, clathrin coats are primarily involved in endocytosis, while COPI and COPII coats play critical roles in the transport of proteins between the Golgi apparatus and the endoplasmic reticulum.

**Clathrin-coated vesicles (CCVs)** are a prominent example of coated vesicles. Clathrin is a triskelion-shaped protein that assembles into a lattice-like structure, forming the characteristic polyhedral shape of CCVs. The assembly of clathrin coats is driven by the interactions between clathrin triskelia and adaptor proteins, such as AP2. These adaptors link cargo molecules, such as transmembrane receptors and signaling molecules, to the clathrin lattice.

**COPI-coated vesicles** are involved in retrograde transport from the Golgi apparatus to the endoplasmic reticulum (ER). COPI coats are composed of seven subunits, including α, β, β′, γ, δ, ε, and ζ. They bind to cargo proteins that have ER retention signals and facilitate their return to the ER.

**COPII-coated vesicles** mediate anterograde transport from the ER to the Golgi apparatus. COPII coats are made up of four major proteins: Sec13/31, Sec23/24, Sar1, and Sec16. They interact with cargo proteins that have ER export signals and direct their movement to the Golgi.

**Retromer** is a protein complex that mediates the retrieval of transmembrane cargo from endosomes to the Golgi apparatus. It consists of a cargo-selective sorting complex (CSC) and a membrane-associated protein complex (MAC). The CSC recognizes specific cargo proteins, while the MAC anchors the retromer complex to the endosomal membrane.

In summary, membrane coats are dynamic and highly organized structures that play essential roles in intracellular trafficking and membrane dynamics. Their assembly and disassembly are tightly regulated, ensuring the accurate and efficient transport of cargo molecules within the cell.'
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Proteins (2)

Compounds (21)