Molecule-receptor binding transducers

The polymers used for fluorescence detection discussed thus far have all used either a synthetically linked polymer as the signal transducer for enhanced detection or some type of hybridization of the polymer with a receptor for ligand-receptor binding signaling. One of the most notable aspects of CPs is their ability to act as direct reporters for the detection of small molecules, or for conformational changes and protein aggregates. 

Cell Surface Receptors These receptors are on the cell surface and have an affinity for hydrophilic binding molecules. Signals are transduced from external stimuli to the cytoplasm and affect cellular pathways via these surface receptors. There are three main superfamilies (groups) of cell surface receptors G-protein coupled receptors, ion channel receptors, and catalytic receptors using enzymatic activities. 

Hormones act by binding to receptors, which are usually protein molecules. Receptors have two functions first, they bind the hormone, and secondly, they transduce (change the type of) the signal to affect the metabolism of the recipient cell. The ability of a cell to respond to a hormone depends on two properties of the receptor molecule how many of them are on a particular cell, and how well they bind the hormone. The first property is called the receptor number, and the second is called the affinity of the receptor for the hormone. The biochemical responsiveness of a cell to a hormone (or a drug, or a neurotransmitter) depends on the number of occupied receptors on the responsive cell. Suppose that a hormone binds to a receptor with a dissociation constant given by the following equation ... 

Physiochemical and structural differences between opioid agonists can influence affinity and binding kinetics at mu receptors, as well as their ability to activate G proteins and other transducer molecules [1,3]. Receptor binding affinity influences agonist association/dis-association kinetics as well as pharmacological onset and duration of activity. The intrinsic efficacy of a given... 

Signal-transducing receptors are plasma membrane proteins that bind specific molecules, such as growth factors, hormones, or neurotransmitters, and then transmit a signal to the cell s interior, causing the cell to respond in a... 

Chemokines are small chemotactic cytokines that act as important messenger molecules between cells of the immune system. Chemokines produce their effects by activating a family of G-protein-coupled receptors. Chemokine receptors are all seven-transmembrane glycoproteins that are structurally related. They may be characterized into those that bind to specific ligands, or those that bind several chemokine ligands. There are also virally encoded (viral) chemokine receptors that represent shared receptors that have been transduced into the viral genome during evolutionary history (Premack and SchaU 1996). 

The most common second messenger activated by protein/peptide hormones and catecholamines is cyclic adenosine monophosphate (cAMP). The pathway by which cAMP is formed and alters cellular function is illustrated in Figure 10.1. The process begins when the hormone binds to its receptor. These receptors are quite large and span the plasma membrane. On the cytoplasmic surface of the membrane, the receptor is associated with a G protein that serves as the transducer molecule. In other words, the G protein acts as an intermediary between the receptor and the second messengers that will alter cellular activity. These proteins are referred to as G proteins because they bind with guanosine nucleotides. In an unstimulated cell, the inactive G protein binds guanosine diphosphate (GDP). When the hormone... 

The neurotrophins interact with two distinct cell surface receptor species [5,6,9] (Fig. 27-2). The neurotrophins bind to the Trk family of receptors, which serve as the principal signal transducer for this class of growth factors. The Trk receptors comprise a small, highly related family of molecules that possess an extracellular ligand binding domain that selectively interacts with the individual neurotrophin species. Trk A specifically binds NGF, TrkB interacts with BDNF and NT4/5, and TrkC preferentially binds NT3. Importantly, the Trk receptors have an intracellular tyrosine kinase domain that is activated upon neurotrophin binding. The kinase domains of the Trk family members are highly conserved and the Trks differ mainly in the structure of their extracellular domains. Trk receptor expression is limited to neurons and the... 

The first molecule, the Ca2+ channel, is required for coupling at the triad. Skeletal muscle contains higher concentrations of this L-type Ca2+ channel that can be accounted for on the basis of measured voltage-dependent Ca2+ influx because much of the Ca2+ channel protein in the T-tubular membrane does not actively gate calcium ion movement but, rather, acts as a voltage transducer that links depolarization of the T-tubular membrane to Ca2+ release through a receptor protein in the SR membrane. The ryanodine receptor mediates sarcoplasmic reticulum Ca2+ release. The bar-like structures that connect the terminal elements of the SR with the T-tubular membrane in the triad are formed by a large protein that is the principal pathway for Ca2+ release from the SR. This protein, which binds the... 

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