About: Cooperativity is a(n) research topic. Over the lifetime, 7027 publication(s) have been published within this topic receiving 258930 citation(s). The topic is also known as: cooperativity.
Papers published on a yearly basis
TL;DR: The criteria for a high affinity, stereoselective, pharmacologically distinct cannabinoid receptor in brain tissue have been fulfilled.
Abstract: The determination and characterization of a cannabinoid receptor from brain are reported. A biologically active bicyclic cannabinoid analgetic CP-55,940 was tritium-labeled to high specific activity. Conditions for binding to rat brain P2 membranes and synaptosomes were established. The pH optimum was between 7 and 8, and specific binding could be eliminated by heating the membranes to 60 degrees. Binding to the P2 membranes was linear within the range of 10 to 50 micrograms of protein/ml. Specific binding (defined as total binding displaced by 1 microM delta 9-tetrahydrocannabinol (delta 9-THC) or 100 nM desacetyllevonantradol) was saturable. The Kd determined from Scatchard analysis was 133 pM, and the Bmax for rat cortical P2 membranes was 1.85 pmol/mg of protein. The Hill coefficient for [3H]CP-55,940 approximated 1, indicating that, under the conditions of assay, a single class of binding sites was determined that did not exhibit cooperativity. The binding was rapid (kon approximately 2.6 x 10(-4) pM-1 min-1) and reversible (Koff approximately 0.016 min-1) and (koff' greater than 0.06 min-1). The two Kd values estimated from the kinetic constants approximately 55 pM and exceeded 200 pM, respectively. The binding of the agonist ligand [3H]CP-55,940 was decreased by the nonhydrolyzable GTP analog guanylylimidodiphosphate. The guanine nucleotide induced a more rapid dissociation of the ligand from the binding site, consistent with an allosteric regulation of the putative receptor by a G protein. The binding was also sensitive to MgCl2 and CaCl2. Binding of [3H]CP-55,940 was displaced by cannabinoid drugs in the following order of potency: CP-55,940 greater than or equal to desacetyllevonantradol greater than 11-OH-delta 9-THC = delta 9-THC greater than cannabinol. Cannabidiol and cannabigerol displaced [3H]CP-55,940 by less than 50% at 1 microM concentrations. The (-)-isomer of CP-55,940 displaced with 50-fold greater potency than the (+)-isomer. This pharmacology is comparable to both the inhibition of adenylate cyclase in vitro and the analgetic activity of these compounds in vivo. The criteria for a high affinity, stereoselective, pharmacologically distinct cannabinoid receptor in brain tissue have been fulfilled.
TL;DR: The helix, s Applequist, 1963) in which the Zimm-Bragg parameters u and s are defined respectively as the cooperativity factor for helix initiation, and the equi- librium constant for converting a coil residue to a helical helix.
Abstract: The helix, s Applequist, 1963) in which the Zimm-Bragg parameters u and s are defined respectively as the cooperativity factor for helix initiation, and the equi- librium constant for converting a coil residue to a helical ~~~~
TL;DR: The 3D structure of the fibrils comprising Aβ(1–42), which was obtained by using hydrogen-bonding constraints from quenched hydrogen/deuterium-exchange NMR, side-chain packing constraints from pairwise mutagenesis studies, and parallel, in-register β-sheet arrangement from previous solid-state NMR studies, explains the sequence selectivity, the cooperativity, and the apparent unidirectionality of Aβ fibril growth.
Abstract: Alzheimer's disease is the most fatal neurodegenerative disorder wherein the process of amyloid-beta (Abeta) amyloidogenesis appears causative. Here, we present the 3D structure of the fibrils comprising Abeta(1-42), which was obtained by using hydrogen-bonding constraints from quenched hydrogen/deuterium-exchange NMR, side-chain packing constraints from pairwise mutagenesis studies, and parallel, in-register beta-sheet arrangement from previous solid-state NMR studies. Although residues 1-17 are disordered, residues 18-42 form a beta-strand-turn-beta-strand motif that contains two intermolecular, parallel, in-register beta-sheets that are formed by residues 18-26 (beta1) and 31-42 (beta2). At least two molecules of Abeta(1-42) are required to achieve the repeating structure of a protofilament. Intermolecular side-chain contacts are formed between the odd-numbered residues of strand beta1 of the nth molecule and the even-numbered residues of strand beta2 of the (n - 1)th molecule. This interaction pattern leads to partially unpaired beta-strands at the fibrillar ends, which explains the sequence selectivity, the cooperativity, and the apparent unidirectionality of Abeta fibril growth. It also provides a structural basis for fibrillization inhibitors.
TL;DR: Ca(2+) regulation of contraction in vertebrate striated muscle is exerted primarily through effects on the thin filament, which regulate strong cross-bridge binding to actin, and the physiological observations of steady-state and transient mechanical behavior are supported.
Abstract: Ca(2+) regulation of contraction in vertebrate striated muscle is exerted primarily through effects on the thin filament, which regulate strong cross-bridge binding to actin. Structural and biochemical studies suggest that the position of tropomyosin (Tm) and troponin (Tn) on the thin filament determines the interaction of myosin with the binding sites on actin. These binding sites can be characterized as blocked (unable to bind to cross bridges), closed (able to weakly bind cross bridges), or open (able to bind cross bridges so that they subsequently isomerize to become strongly bound and release ATP hydrolysis products). Flexibility of the Tm may allow variability in actin (A) affinity for myosin along the thin filament other than through a single 7 actin:1 tropomyosin:1 troponin (A(7)TmTn) regulatory unit. Tm position on the actin filament is regulated by the occupancy of NH-terminal Ca(2+) binding sites on TnC, conformational changes resulting from Ca(2+) binding, and changes in the interactions among Tn, Tm, and actin and as well as by strong S1 binding to actin. Ca(2+) binding to TnC enhances TnC-TnI interaction, weakens TnI attachment to its binding sites on 1-2 actins of the regulatory unit, increases Tm movement over the actin surface, and exposes myosin-binding sites on actin previously blocked by Tm. Adjacent Tm are coupled in their overlap regions where Tm movement is also controlled by interactions with TnT. TnT also interacts with TnC-TnI in a Ca(2+)-dependent manner. All these interactions may vary with the different protein isoforms. The movement of Tm over the actin surface increases the "open" probability of myosin binding sites on actins so that some are in the open configuration available for myosin binding and cross-bridge isomerization to strong binding, force-producing states. In skeletal muscle, strong binding of cycling cross bridges promotes additional Tm movement. This movement effectively stabilizes Tm in the open position and allows cooperative activation of additional actins in that and possibly neighboring A(7)TmTn regulatory units. The structural and biochemical findings support the physiological observations of steady-state and transient mechanical behavior. Physiological studies suggest the following. 1) Ca(2+) binding to Tn/Tm exposes sites on actin to which myosin can bind. 2) Ca(2+) regulates the strong binding of M.ADP.P(i) to actin, which precedes the production of force (and/or shortening) and release of hydrolysis products. 3) The initial rate of force development depends mostly on the extent of Ca(2+) activation of the thin filament and myosin kinetic properties but depends little on the initial force level. 4) A small number of strongly attached cross bridges within an A(7)TmTn regulatory unit can activate the actins in one unit and perhaps those in neighboring units. This results in additional myosin binding and isomerization to strongly bound states and force production. 5) The rates of the product release steps per se (as indicated by the unloaded shortening velocity) early in shortening are largely independent of the extent of thin filament activation ([Ca(2+)]) beyond a given baseline level. However, with a greater extent of shortening, the rates depend on the activation level. 6) The cooperativity between neighboring regulatory units contributes to the activation by strong cross bridges of steady-state force but does not affect the rate of force development. 7) Strongly attached, cycling cross bridges can delay relaxation in skeletal muscle in a cooperative manner. 8) Strongly attached and cycling cross bridges can enhance Ca(2+) binding to cardiac TnC, but influence skeletal TnC to a lesser extent. 9) Different Tn subunit isoforms can modulate the cross-bridge detachment rate as shown by studies with mutant regulatory proteins in myotubes and in in vitro motility assays. (ABSTRACT TRUNCATED)