Ligand Fitting
Ligand Fitting - Related Videos
02:40
Ligand Binding Sites
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2020
Proteins are dynamic macromolecules that carry out a wide variety of essential processes; however, the activities of most proteins depend on their interactions with other molecules or ions, known as ligands. Protein-ligand interactions are quite specific; even though numerous potential ligands surround a cellular protein at any given time, only a particular ligand can bind to that protein. Moreover, a ligand binds only to a dedicated area on the surface of the protein, known as the...
02:51
Metal-Ligand Bonds
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2020
The hemoglobin in the blood, the chlorophyll in green plants, vitamin B-12, and the catalyst used in the manufacture of polyethylene all contain coordination compounds. Ions of the metals, especially the transition metals, are likely to form complexes. In these complexes, transition metals form coordinate covalent bonds, a kind of Lewis acid-base interaction in which both of the electrons in the bond are contributed by a donor (Lewis base) to an electron acceptor (Lewis acid). The Lewis acid in...
00:49
Ligand Binding and Linkage
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2020
Allosteric proteins have more than one ligand binding site; the binding of a ligand to any of these sites influences the binding of ligands to the other sites. When a protein is allosteric, its binding sites are called coupled or linked. In the case of enzymes, the site that binds to the substrate is known as the active site and the other site is known as the regulatory site. When a ligand binds to the regulatory site, this leads to conformational changes in the protein that can influence the...
01:13
Induced-fit Model
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2019
Most chemical reactions in cells require enzymes—biological catalysts that speed up the reaction without being consumed or permanently changed. They reduce the activation energy needed to convert the reactants into products. Enzymes are proteins, that usually work by binding to a substrate—a reactant molecule that they act upon. Enzymes exhibit substrate specificity, meaning that they can only bind to certain substrates. This is mainly determined by the shape and chemical characteristics of...
08:45
Isothermal Titration Calorimetry for Measuring Macromolecule-Ligand Affinity
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Cited by 84 •
2011
A general protocol for the use of isothermal titration calorimetry to monitor the binding thermodynamics for biological systems with moderate binding affinities is presented.
FAQs
Electron density provides the experimental signal against which a ligand model is evaluated. Software compares the proposed atomic arrangement with that density and adjusts the ligand’s position, orientation, and conformation to improve agreement. This relationship helps distinguish a plausible binding pose from one that merely appears chemically reasonable but does not adequately match the crystallographic evidence.
Chemical geometry restraints prevent refinement from producing unreasonable bond lengths, bond angles, or related structural features while the model is adjusted to fit electron density. They create a balance between experimental agreement and chemically credible structure. This is especially important when the density is not sufficient by itself to define every aspect of the ligand conformation confidently.
The fitting process evaluates three central aspects of a ligand model: its position within the binding site, its orientation, and its conformation. Refining these variables changes how the atoms occupy the observed density and how the molecule is arranged relative to the macromolecule. Their combined adjustment determines whether the resulting pose provides a consistent structural interpretation.
A useful model must satisfy two requirements at once: it should agree with the experimental electron density and preserve reasonable chemical geometry. A pose that fits density but distorts bonds or angles is not reliable, while a chemically tidy pose that disagrees with the density is also problematic. Considering both criteria supports more defensible interpretation of binding-site structures.
An accurately fitted ligand model can reveal how the small molecule is positioned in a binding site and which structural features may contribute to its interactions with the macromolecule. These observations help researchers interpret binding-site organization and examine enzyme mechanisms. The resulting model also provides a basis for comparing ligand poses across related structures.
Reliable ligand poses support compound design by showing how candidate molecules occupy a macromolecular binding site. Researchers can compare these poses to guide optimization for improved activity or selectivity. Because the interpretation depends on a structurally credible model, fitting also helps ensure that decisions about molecular changes are based on ligand arrangements consistent with experimental density and chemical geometry.