Biomaterial Database

Linkages between the dissociation of alpha beta tubulin into subunits and ligand binding: the ground state of tubulin is the GDP conformation. 1994

K E Shearwin, and B Perez-Ramirez, and S N Timasheff

Graduate Department of Biochemistry, Brandeis University, Waltham, Massachusetts 02254-9110.

The effects of ligands on the dissociation of the alpha beta tubulin dimer into the two subunits were investigated using calf brain tubulin. Sedimentation equilibrium studies showed a number of linkages. In the absence of magnesium in the medium, tubulin-GTP, tubulin-GDP, and tubulin with the exchangeable site unoccupied associate with essentially the same strength (K alpha beta = 1 x 10(7) M-1). This indicates that the ground state of tubulin (i.e., in the absence of magnesium) is not affected by occupancy of the exchangeable nucleotide binding site (E site). The alpha beta association is enhanced by magnesium ions. The association of tubulin with GDP in the E site is linked to the uptake of twice as many magnesium ions as that of tubulin with GTP in the E site. This suggests that magnesium binding is linked to an E-site-related conformational change. Consideration of the linkages between the binding of magnesium ions, E-site occupancy, and tubulin conformation in terms of the model [Howard, W. D., & Timasheff, S. N. (1986) Biochemistry 25, 8292-8300] in which the tubulin alpha beta dimer exists in an equilibrium between two conformations, a microtubule-forming ("straight") state favored by GTP and a double-ring-forming ("curved") state favored by GDP, leads to the conclusion that the ground state of tubulin is the ring-forming or "curved" conformation. Thus, in the absence of magnesium, the tubulin heterodimer exists in the ring-forming conformation, whether the E site is occupied by GTP or GDP.(ABSTRACT TRUNCATED AT 250 WORDS)

UI	MeSH Term	Description	Entries
D007477	Ions	An atom or group of atoms that have a positive or negative electric charge due to a gain (negative charge) or loss (positive charge) of one or more electrons. Atoms with a positive charge are known as CATIONS; those with a negative charge are ANIONS.
D008024	Ligands	A molecule that binds to another molecule, used especially to refer to a small molecule that binds specifically to a larger molecule, e.g., an antigen binding to an antibody, a hormone or neurotransmitter binding to a receptor, or a substrate or allosteric effector binding to an enzyme. Ligands are also molecules that donate or accept a pair of electrons to form a coordinate covalent bond with the central metal atom of a coordination complex. (From Dorland, 27th ed)	Ligand
D008870	Microtubules	Slender, cylindrical filaments found in the cytoskeleton of plant and animal cells. They are composed of the protein TUBULIN and are influenced by TUBULIN MODULATORS.	Microtubule
D009690	Nucleic Acid Conformation	The spatial arrangement of the atoms of a nucleic acid or polynucleotide that results in its characteristic 3-dimensional shape.	DNA Conformation,RNA Conformation,Conformation, DNA,Conformation, Nucleic Acid,Conformation, RNA,Conformations, DNA,Conformations, Nucleic Acid,Conformations, RNA,DNA Conformations,Nucleic Acid Conformations,RNA Conformations
D002417	Cattle	Domesticated bovine animals of the genus Bos, usually kept on a farm or ranch and used for the production of meat or dairy products or for heavy labor.	Beef Cow,Bos grunniens,Bos indicus,Bos indicus Cattle,Bos taurus,Cow,Cow, Domestic,Dairy Cow,Holstein Cow,Indicine Cattle,Taurine Cattle,Taurus Cattle,Yak,Zebu,Beef Cows,Bos indicus Cattles,Cattle, Bos indicus,Cattle, Indicine,Cattle, Taurine,Cattle, Taurus,Cattles, Bos indicus,Cattles, Indicine,Cattles, Taurine,Cattles, Taurus,Cow, Beef,Cow, Dairy,Cow, Holstein,Cows,Dairy Cows,Domestic Cow,Domestic Cows,Indicine Cattles,Taurine Cattles,Taurus Cattles,Yaks,Zebus
D006153	Guanosine Diphosphate	A guanine nucleotide containing two phosphate groups esterified to the sugar moiety.	GDP,Guanosine 5'-Diphosphate,Guanosine 5'-Trihydrogen Diphosphate,5'-Diphosphate, Guanosine,5'-Trihydrogen Diphosphate, Guanosine,Diphosphate, Guanosine,Diphosphate, Guanosine 5'-Trihydrogen,Guanosine 5' Diphosphate,Guanosine 5' Trihydrogen Diphosphate
D006160	Guanosine Triphosphate	Guanosine 5'-(tetrahydrogen triphosphate). A guanine nucleotide containing three phosphate groups esterified to the sugar moiety.	GTP,Triphosphate, Guanosine
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D001665	Binding Sites	The parts of a macromolecule that directly participate in its specific combination with another molecule.	Combining Site,Binding Site,Combining Sites,Site, Binding,Site, Combining,Sites, Binding,Sites, Combining
D013816	Thermodynamics	A rigorously mathematical analysis of energy relationships (heat, work, temperature, and equilibrium). It describes systems whose states are determined by thermal parameters, such as temperature, in addition to mechanical and electromagnetic parameters. (From Hawley's Condensed Chemical Dictionary, 12th ed)	Thermodynamic