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UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-24 9:27 |
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Conference: Bucharest University Faculty of Physics 2011 Meeting
Section: Biophysics; Medical Physics
Title:
Specific interactions the sine qua non for life processes
Authors:
Gabriel Baranga, Doina Gazdaru, Claudia Chilom, Aurel Popescu
Affiliation:
Research Centre in Molecular Biophysics, Department of Electricity Solid State and Biophysics,
Faculty of Physics, University of Bucharest
E-mail
aurel.popescu.46@gmail.com
Keywords:
Specific interactions, affinity constant, ligands, substrates
Abstract:
Life processes are possible only by myriads of correlated biomolecular interactions permanently taking place in all the cells. The most important biomolecular interactions are the specific interactions, conducting to preferential associations between partners. The specific interactions are the result of many synergic factors: a) geometrical shape and electrical charge complementarity of the two partner “surfaces” b) the extensive network of hydrogen bonds formed in the binding site; c) the numerous van der Waals contacts and hydrophobic interactions d) the rigidization of a flexible loop which closes over the bound partner (e.g., ligand), acting like a `lid`. The most interesting specific interactions are the enzyme substrate interactions and the protein-ligand interactions. For enzymes, the natural ligands are the specific substrates which are previously bound to enzyme active sites and then split into products. On the other hand, the external membrane receptors (which are proteins) bind the specific ligands without being chemically modified. In this case, the intact ligands are inducing conformational (allosteric) changes in the receptor proteins. The cellular functions of most proteins are controlled by small ligands that reversibly bind to proteins stimulating (the case of agonists) or inhibiting (the case of antagonists) their functions. The specific interactions are characterized by the affinity constant, Ka, a high affinity meaning a great value for Ka.. The affinity constant for specific interactions, can vary over many orders of magnitude: from ~ 10^4 to 10^10 M^-1. For example, the Xeroderma pigmentosum group C protein binds to human centrin 2, with a Ka of ~ 10^8 M^-1, while the highly specific interaction between some IgG antibodies and their antigens is characterized by an affinity constant of 10^9 M^-1. In the case of association, streptavidin-biotin the affinity constant is even higher. In fact, this is one of the strongest non-covalent interactions known in Nature with Ka = 10^14 M^-1!
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