Receptor refers to any biological macromolecule that can combine with hormones, neurotransmitters, drugs or intracellular signal molecules and cause changes in cell function.[1]
According to the position of receptors in cells, they can be divided into cell surface receptors and intracellular receptors.The receptor itself contains at least two active sites: one is the active site that recognizes and binds ligands;The other is the functional active site responsible for generating response response. This site can generate response response only after it is combined with the ligand to form a binary complex and allosteric, thus starting a series of biochemical reactions, and ultimately leading to biological effects of target cells.
1. Cell membrane receptor
Most ligand signal molecules are hydrophilic biological macromolecules, such as cytokines, protein polypeptide hormones, water-soluble hormones, prostaglandins, hydrophilic neurotransmitters, etc. Since they cannot penetrate the target cell membrane into the cell, the receptors of these ligand signal molecules are located on the target cell membrane.
2. Intracellular receptors
The receptor of most ligand signal molecules is on the surface of the target cell, because the signal molecules are hydrophilic and cannot pass through the cell membrane.However, some ligand signal molecules can directly pass through the target cell membrane and interact with the cytoplasmic or nuclear receptors. By regulating the transcription of specific genes, the expression of gene expression products can be up or down regulated, thus starting a series of biochemical reactions, and ultimately leading to biological effects in target cells.Such signal molecules include fat soluble steroid hormones, thyroid hormones, retinoic acid and gaseous nitric oxide.
function
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The receptor has two functions:
The first function is to recognize their own specific signal molecules (ligands) and bind to them.It is through the recognition of receptors and signal ligand molecules that cells can recognize and receive a specific signal in an environment full of numerous biological molecules.The second function is to accurately amplify and transmit the recognized and received signals to the cell interior, thus starting a series of intracellular signal cascade reactions, and finally leading to specific cellular biological effects.
Characteristics of receptor ligand binding
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The binding between receptor and ligand results in the activation of receptor and the basic steps of subsequent signal transmission of receptor activation.Under physiological conditions, the binding between receptor and ligand is not mediated by covalent bond, but mainly depends on ionic bond, hydrogen bond, van der Waals force and hydrophobic interaction.When binding with ligand, receptor has the characteristics of saturation, high affinity, specificity, reversibility and so on.
