Biomaterial Database

Liver cytosol corticosteroid binder IB, a new binding protein. 1975

G Litwack, and S A Rosenfield

A new binding protein named corticosteroid Binder IB elutes just after ligandin in DEAE-Sephadex chromatograms. It has been partially purified to about 2500-fold over cytosol proteins. Calculation of the number of steroid binding sites, assuming one site per molecule of Binder IB fraction after DEAE-Sephadex chromatography, suggests a concentration of the binding protein of about 0.0004% of cytosol proteins. Its pI value is judged to be 7.5 to 8 from it elution position on DEAE-Sephadex chromatograms. IB has an apparent molecular weight of 30,500 +/- 10% by gel filtration and a Stokes radius of 20 A. Binder IB binds radioactive dexamethasone, cortisol, and corticosterone in vitro with estimated KD values of 1, 13, and 25 nM, respectively. Saturation curves are abnormal, showing two phases. The saturation curves within the physiological range of concentrations of steroid are abnormal and suggestive of cooperativity. The second phase, at concentrations of glucocortidoids above saturation and physiological levels, shows extensive binding. After fractionation from other steroid binding proteins, the specificity of binding from competition studies in vitro is dexamethasone greater than or equal to cortisol = corticosterone = estradiol-17beta greater than or equal to deoxycorticosterone = dihydrotestosterone greater than aldosterone = cortexolone greater than testosterone. Other steroids tested are less efficient ligands. The binding is probably noncovalent, but strong; and the complex becomes more dissociable as purification proceeds, suggesting a conformational change in the protein. Storage and rebinding with steroid are possible throughout the purification process, although extensive ligand dissociation and denaturation of the protein occur after the final purification step. Binding in vitro is temperature-sensitive and binding is sharply pH dependent with an optimum at 7.5. The ligand is the unmetabolized steroid as judged by extraction of steroid-IB complex with methylene chloride and subsequent thin layer chromatography. The physiological function of this protein is unknown at present and purification fo the major corticosteroid hormone receptor to homogeneity may be required before the function of Binder IB is fully understood.

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008099	Liver	A large lobed glandular organ in the abdomen of vertebrates that is responsible for detoxification, metabolism, synthesis and storage of various substances.	Livers
D008297	Male		Males
D008970	Molecular Weight	The sum of the weight of all the atoms in a molecule.	Molecular Weights,Weight, Molecular,Weights, Molecular
D011485	Protein Binding	The process in which substances, either endogenous or exogenous, bind to proteins, peptides, enzymes, protein precursors, or allied compounds. Specific protein-binding measures are often used as assays in diagnostic assessments.	Plasma Protein Binding Capacity,Binding, Protein
D011506	Proteins	Linear POLYPEPTIDES that are synthesized on RIBOSOMES and may be further modified, crosslinked, cleaved, or assembled into complex proteins with several subunits. The specific sequence of AMINO ACIDS determines the shape the polypeptide will take, during PROTEIN FOLDING, and the function of the protein.	Gene Products, Protein,Gene Proteins,Protein,Protein Gene Products,Proteins, Gene
D011956	Receptors, Cell Surface	Cell surface proteins that bind signalling molecules external to the cell with high affinity and convert this extracellular event into one or more intracellular signals that alter the behavior of the target cell (From Alberts, Molecular Biology of the Cell, 2nd ed, pp693-5). Cell surface receptors, unlike enzymes, do not chemically alter their ligands.	Cell Surface Receptor,Cell Surface Receptors,Hormone Receptors, Cell Surface,Receptors, Endogenous Substances,Cell Surface Hormone Receptors,Endogenous Substances Receptors,Receptor, Cell Surface,Surface Receptor, Cell
D003345	Corticosterone	An adrenocortical steroid that has modest but significant activities as a mineralocorticoid and a glucocorticoid. (From Goodman and Gilman's The Pharmacological Basis of Therapeutics, 8th ed, p1437)
D003600	Cytosol	Intracellular fluid from the cytoplasm after removal of ORGANELLES and other insoluble cytoplasmic components.	Cytosols
D003907	Dexamethasone	An anti-inflammatory 9-fluoro-glucocorticoid.	Hexadecadrol,Decaject,Decaject-L.A.,Decameth,Decaspray,Dexasone,Dexpak,Hexadrol,Maxidex,Methylfluorprednisolone,Millicorten,Oradexon,Decaject L.A.