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Binding of a ligand to a binding site on protein often triggers a change in conformation in the protein and results in altered cellular function. Hence binding site on protein are critical parts of signal transduction pathways. [10] Types of ligands include neurotransmitters, toxins, neuropeptides, and steroid hormones. [11]
The first description of cooperative binding to a multi-site protein was developed by A.V. Hill. [4] Drawing on observations of oxygen binding to hemoglobin and the idea that cooperativity arose from the aggregation of hemoglobin molecules, each one binding one oxygen molecule, Hill suggested a phenomenological equation that has since been named after him:
One manifestation of this is enzymes or receptors that have multiple binding sites where the affinity of the binding sites for a ligand is apparently increased, positive cooperativity, or decreased, negative cooperativity, upon the binding of a ligand to a binding site. For example, when an oxygen atom binds to one of hemoglobin's four binding ...
Each curve corresponds to a different Hill coefficient, labeled to the curve's right. The vertical axis displays the proportion of the total number of receptors that have been bound by a ligand. The horizontal axis is the concentration of the ligand. As the Hill coefficient is increased, the saturation curve becomes steeper.
In DNA-ligand binding studies, the ligand can be a small molecule, ion, [1] or protein [2] which binds to the DNA double helix. The relationship between ligand and binding partner is a function of charge, hydrophobicity, and molecular structure. Binding occurs by intermolecular forces, such as ionic bonds, hydrogen bonds and Van der Waals forces.
Molecular binding occurs in biological complexes (e.g., between pairs or sets of proteins, or between a protein and a small molecule ligand it binds) and also in abiologic chemical systems, e.g. as in cases of coordination polymers and coordination networks such as metal-organic frameworks.
However, for many cell surface receptors, ligand-receptor interactions are not directly linked to the cell's response. The activated receptor must first interact with other proteins inside the cell before the ultimate physiological effect of the ligand on the cell's behavior is produced. Often, the behavior of a chain of several interacting ...
It is associated with the binding and unbinding reaction of receptor (R) and ligand (L) molecules, which is formalized as: R + L ⇌ RL. The reaction is characterized by the on-rate constant k on and the off-rate constant k off, which have units of M −1 s −1 and s −1, respectively. In equilibrium, the forward binding transition R + L → ...