Vesicle transport is that macromolecular substances and granular substances cannot pass through the cell membrane. It is transported across the cell membrane in another special way, that is, the substance is covered by the membrane, forms vesicles, and Membrane fusion or rupture is completed, so it is also called vesicle transport.
Vesicles are very common membrane structures in eukaryotic cells. It does not exist as a relatively stable intrinsic cellular structure like the endoplasmic reticulum, Golgi complex, lysosome and peroxisome, but it is still an indispensable important functional structural component and Vector functions and manifestations of intracellular substance-directed transport. There are at least 10 types of vesicles responsible for the targeted transport of intracellular materials. Clathrin with vesicles, COPI and COPⅡ with vesicles are the three types of vesicles that are well known. Clathrin has the involvement of clathrin, adapter protein, and dynein to form vesicles.
This method is mainly seen in the transport of proteins between organelles, such as the transport of proteins from the endoplasmic reticulum to the Golgi apparatus and from the Golgi apparatus to lysosomes, secretory vesicles, cytoplasmic membranes, extracellular and so on. Vesicle transport process is called vesicle transport. Transport vesicles have a diameter of 50-100 nm and are usually formed in a budding manner from one organelle. The vesicles contain the transported protein. When it reaches the target organelle, it fuses with it and transports the protein from one organelle to another. The transport of proteins through the secretory pathway can be divided into at least three different stages. First, the protein is exported from the endoplasmic reticulum and then presented to the Golgi apparatus; second is the transport within the Golgi apparatus; and finally the transport after the Golgi apparatus. This step includes Transport of proteins from the reverse Golgi network of the Golgi apparatus to the endosome and plasma membrane. The transport of proteins from the endoplasmic reticulum to the Golgi apparatus and within the Golgi apparatus is concentrated, often referred to as the quality control of secreted proteins. Although vesicles can be considered as one of the important overall functional structural components of the endometrial system. However, unlike membrane organelles such as the endoplasmic reticulum, Golgi complex, lysosome, and peroxisome, they are not a relatively stable intrinsic structure in the cell, but only a carrier and functional manifestation of the intracellular material directed transport.
Clathrin vesicles are the most thoroughly studied type of vesicles. The surface of such vesicles is covered with a layer of fibrous filamentous protein, which is named as a grid. The typical clathrin has a vesicle diameter that is generally between 50 and 100 nm. The cytoplasmic membrane is concave, or the Golgi body is opposite to the convex sac of the membrane. Grid egg gate molecules are composed of 3 heavy chains and 3 light chains. Each heavy chain is combined with a light chain to form an abducted arm. The 3 arms are combined to form a clathrin. Spatial structure, so clathrin is also called three-arm protein. The molecular weight of clathrin heavy chain is 180KD, and the light chain is 35-40KD. Clathrin covers the surface of spherical transport vesicles, which greatly increases the tension of the latter.
Figure 1. Cartoon representation of the molecular structure of protein registered with 1c9l code.
Clathrins themselves cannot capture transport molecules, and their vesicle-capture specific molecules rely on adapter proteins to achieve them. On the one hand, the adapter protein forms the inner structure of the vesicle relative to the outer clathrin framework, and on the other hand, it also mediates the connection of clathrin with the transmembrane receptor of the capsule, thereby forming and maintaining the clathrin-vesicle. Integrated structural system. There are four kinds of adapter proteins that have been discovered. They selectively bind to different receptor-transporter molecular complexes to form specific transport vesicles for different substance transport. As a result of this complex interaction, the transported substances with vesicles entering the grid are concentrated. Among them, three adapter proteins (AP1, AP2, and AP3) have been identified.
Figure 2. Adaptor protein
The production of clathrin vesicles is a very complicated process, involving the participation and role of many factors. In the formation of vesicles, in addition to clathrin and adaptor proteins, dynein is also referred to as chopped protein-a special protein in the cytoplasm that can bind and hydrolyze GTP, which has an extremely important role. The prion protein is composed of 900 amino acids. When the membrane sac buds form, the prion protein binds to GTP and aggregates to form a ring in the neck of the convex (or concave) budding membrane sac. The pinch protein ring constricted to the heart until the vesicles break off and form. Once the vesicles sprout, they will immediately take off the clathrin cover, transform into non-transported vesicles, and begin the transport operation.
Figure 3. Cytoplasmic dynein on a microtubule.
1. Samora CP.; et al. MAP4 and CLASP1 operate as a safety mechanism to maintain a stable spindle position in mitosis. Nature Cell Biology. 2011, 13 (9): 1040–50.