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Allosteric regulation of an enzyme. In the fields of biochemistry and pharmacology an allosteric regulator (or allosteric modulator) is a substance that binds to a site on an enzyme or receptor distinct from the active site, resulting in a conformational change that alters the protein's activity, either enhancing or inhibiting its function.
On the other hand, a protein may interact briefly and in a reversible manner with other proteins in only certain cellular contexts – cell type, cell cycle stage, external factors, presence of other binding proteins, etc. – as it happens with most of the proteins involved in biochemical cascades. These are called transient interactions.
Single-chain sites (of “monodesmic” ligands, μόνος: single, δεσμός: binding) are formed by a single protein chain, while multi-chain sites (of "polydesmic” ligands, πολοί: many) [26] are frequent in protein complexes, and are formed by ligands that bind more than one protein chain, typically in or near protein interfaces ...
Efflux pumps generally consist of an outer membrane efflux protein, a middle periplasmic protein, an inner membrane protein, and a transmembrane duct. The transmembrane duct is located in the outer membrane of the cell. The duct is also bound to two other proteins: a periplasmic membrane protein and an integral membrane transporter.
Cell membrane receptors can be further classified into ion channel linked receptors, G-Protein coupled receptors and enzyme linked receptors. Ion channels receptors are large transmembrane proteins with a ligand activated gate function. When these receptors are activated, they may allow or block passage of specific ions across the cell membrane.
When a surface is exposed to a multi-protein solution, adsorption of certain protein molecules are favored over the others. Protein molecules approaching the surface compete for binding sites. In multi-protein system attraction between molecules can occur, whereas in single-protein solutions intermolecular repulsive interactions dominate.
Protein folding must be thermodynamically favorable within a cell in order for it to be a spontaneous reaction. Since it is known that protein folding is a spontaneous reaction, then it must assume a negative Gibbs free energy value. Gibbs free energy in protein folding is directly related to enthalpy and entropy. [12]
This process is called promoter escape, and is another step at which regulatory elements can act to accelerate or slow the transcription process. Similarly, protein and nucleic acid factors can associate with the elongation complex and modulate the rate at which the polymerase moves along the DNA template.