Signal transduction refers to the process by which a cell stimulates an information molecule through a membrane or an intracellular receptor, and is transformed by an intracellular signal transduction system, thereby affecting the biological function of the cell. Water-soluble information molecules and prostaglandins (lipid-soluble) must first bind to the membrane receptor, initiate a cascade of intracellular signal transduction, transduce the extracellular signal transmembrane into the cell; fat-soluble information molecules can enter the cell, bind to the cytoplasmic or nuclear receptor, and induce a cell-specific response by altering the transcriptional activity of the target gene.
1. Cyclic receptor (ion channel receptor)
Most of cyclic receptor are neurotransmitter receptors, the receptor molecules constitute ion channels. The receptor binds to the signal molecule and becomes allosteric, causing the channel to open or close and a rapid transient effect.
2. Serpentine receptor
There are more than 100 transmembrane α-helical receptors, all of which are single polypeptide glycoproteins, such as G protein-coupled receptors.
3. Single transmembrane alpha-helical receptor
Single transmembrane alpha-helical receptor included tyrosine protein kinase receptors and non-tyrosine protein kinase receptors.
(1) Such receptors as protein kinase receptors include growth factor receptors, insulin receptors and so on. After binding to the corresponding ligand, the receptor dimerizes or multimerizes, exhibits tyrosine protein kinase activity, catalyzes the phosphorylation of the receptor itself and the substrate tyrosine.
(2) Non-tyrosine protein kinase receptors, such as growth hormone receptors, interferon receptors, and so on. When the receptor binds to the ligand, a different downstream non-receptor type TPK can be coupled and activated to deliver a regulatory signal.
Intracellular receptor located in the cytosol or nucleus, after binding to the signal molecule, the receptor acts as a trans-acting factor that binds to the DNA cis-acting element and activates gene transcription and expression, including steroid hormone receptors, thyroid hormone receptors and so on. The intracellular receptors are all single-chain proteins with four structural regions: highly variable region, DNA binding region, hormone binding region and hinge region.
Interaction characteristics:1 high affinity, 2 highly specific, 3 saturable
1. Receptor: A special protein located on or in the cell membrane that specifically recognizes and binds to biologically active molecules, thereby causing biological effects. The membrane receptors are mostly mosaic glycoproteins: all intracellular receptors are DNA-binding proteins. Receptors play an extremely important role in the process of cell information transmission.
2. G protein: guanylate-binding protein, is a kind of peripheral protein that is located on the cytoplasmic surface of cell membrane and can bind to GDP or GTP. It consists of three subunits: α, β and γ. It is a non-activated type that exists as a trimer and binds to GDP. When the α subunit binds to GTP and causes the βγ dimer to shed, it becomes activated, which acts on different hormones of the membrane receptor, and mediates the activity of certain ion channels or enzymes on the plasma membrane through different G proteins. Thereby affecting the intracellular second messenger concentration and subsequent biological effects.
Apoptosis is an active signal-dependent process that can be induced by many factors, such as radiation exposure, ischemia and hypoxia, viral infections, drugs, and toxins. Most of these factors trigger the mechanism of apoptosis by activating death receptors. Death receptors are present on the cell surface. It belongs to the tumor necrosis factor receptor superfamily. When they are activated by binding to the corresponding ligands or antibodies, their cytoplasmic regions can bind to some signal transduction proteins, of which cytoplasmic proteins containing the death domain are important. They bind to the death receptor via the death domain, and also bind to the downstream capase protease, allowing the death signal on the cell membrane surface to be transmitted to the cell.