Functionalized receptor

The relationship between the two receptors for NGF is complex and not yet completely understood. It has been suggested that the functional form of the NGF receptor is a heterodimer of p75 and pl40 proteins. BDNF and NT-3 bind to p75, but the functional receptors for these neurotrophins are the proto-oncogene products of and trkQ. 

The number of functioning receptors controls the magnitude of the initial stimulus given to the cell by an agonist. Number of receptors on the cell surface is one means the cell can control its stimulatory environment. Thus, it is not surprising that receptor density varies with different cell types. Potentially, this can be used to control... 

HT3 receptors are an exception to the general nomenclature of numbering subunits and denoting stoichiometry by subscripts. The 5-HT3 receptor subtype is denoted by the subscript 3 and the two known subunits are referred to as A and B . When expressed alone, 5-HT3-A subunits form functional homomeric receptors but these have a much smaller single channel conductance (less than 1.0 pS) and altered pharmacology compared to native 5-HT3 receptors. Native 5-HT3 receptors are likely to be pentameric heteromers of 5-HT3-A and 5-HT3-B subunits. 5-HT3-B subunits, unlike 5-HT3-A subunits, do not form functional receptors when expressed alone but when co-expressed with 5-HT3-A subunits, the receptors formed have functional properties similar to native 5-HT3 receptors. Synaptic transmission mediated by 5-HT3 receptors has been... 

Heterologous desensitisation refers to the desensitisation of the response to one agonist by the application of a different agonist. For example, desensitisation of a response to adrenaline by application of 5-HT is mediated by protein kinase A or protein kinase C because these kinases can phosphorylate receptors which are not occupied by agonist. Phosphorylation disrupts the receptor-G-protein interaction and induces the binding of specific proteins, arrestins which enhance receptors internalisation via clathrin-coated pits. Thus desensitisation of G-protein-coupled receptors results in a decrease in the number of functional receptors on the cell surface. 

Lasagni L, Francalanci M, Annunziato F, et al. An alternatively spliced variant of CXCR3 mediates the inhibition of endothelial cell growth induced by IP-10, Mig, and I-TAC, and acts as functional receptor for platelet factor 4. J Exp Med 2003 197(11) 1537—1549. 

The diversity of the GABAa subunits (Figure 3.2d) is reflected in a very complex pharmacology. Expression of the subunits in heterologous systems shows that the combinations a, (3, and y can yield functional receptors, indicating that the limitation in subunit combination is defined by expression levels and most likely cell-dependent assembly mechanisms also. The pj to p3 subunits mainly co-assemble with each other to form the GABAC receptors. 

The kainate receptors are composed of subunits from the GluR5-GluR7 class and the KA1-KA2 class of subunits. Homomeric receptors of the former class generate functional receptors and bind kainate with an affinity of 50 to 100 nM. KA1 or KA2 do not generate functional channels, but the receptors bind kainate with an affinity of 5 to 10 nM. Homomeric GluR6 and KA2 receptors are neither activated by AMPA, nor do they bind AMPA. Interestingly, when they are co-expressed, heteromeric receptors respond to AMPA. 

Schmidt I don t know whether I can answer the why question, but the how question has a conceptual framework to build it around. What you are looking for is some kind of phosphorylation target of cyclin B that is a non-cell cycle functioning receptor. You are looking for some cell cycle receptor sitting in the membrane that cyclin B goes over to, puts the phosphate on, activates it and says now I am receptive . 

Beauchamp, C.O., Gonias, S.L., Menapace, D.P., and Pizzo, S.V. (1983) A new procedure for the synthesis of polyethylene glycol-protein adducts Effects on function, receptor recognition, and clearance of superoxide dismutase, lactoferrin, and a2macroglobulin. Anal. Biochem. 131, 25-33. 

The answer is a. (Katzung, p 590.) Bile acids are absorbed primarily in the ileum of the small intestine. Cholestyramine binds bile acids, preventing their reabsorption in the jejunum and ileum. Up to 10-fold greater excretion of bile acids occurs with the use of resins. The increased clearance leads to increased cholesterol turnover of bile acids. Low-density lipoprotein receptor upregulation results in increased uptake of LDL. This does not occur in homozygous familial hypercholesterolemia because of lack of functioning receptors. 

The intrinsic complexity and the multiplicity of cholinergic receptors became evident upon elucidation of their primary structures. In the CNS, at least nine different sequences of a subunits and three different sequences of (3 subunits of the nicotinic receptor have been identified [10, 11]. Expression of the cloned genes encoding certain subunit combinations yields functional receptors with different sensitivities toward various toxins and agonists. 

GABAb receptors are heterodimers. Two GABAb receptor subunits have been cloned, R1 and R2. Neither of these appears to express functional receptors on their own, but they are active when coexpressed, suggesting that a dimer is trafficked to the cell surface and forms an active complex. Evidence shows that the R1 subunit contains the GABA binding site while the R2 subunit interacts with the G protein [14]. 

AA metabolites and PAF have initially been studied in terms of their roles in the inflammatory response, such as increased vascular permeability and the activation of and infiltration by inflammatory cells. It is now becoming apparent, however, that these bioactive lipids have significant neurobiological actions in ion channel functions, receptors, neurotransmitter release, synaptic plasticity and neuronal gene expression. 

The general mechanism of Ca2+ wave propagation is believed to be as follows. An event occurs that results in a small rise of intracellular Ca2+ near an SR release receptor (either ryanodine receptor or inositol-1,4,5-trisphosphate [InsPs] receptor). The release of SR Ca2+ results in a local increase of cytoplasmic Ca2+. The nascent cytoplasmic Ca2+ then diffuses to adjacent release sites, causing further SR release. This process is a regenerative process and will remain so as long as the receptors are functional and the SR Ca2+ stores are sufficient. The Ca2+ wave can then be envisioned as a series of SR Ca2+ release events that are dependent upon local Ca2+ concentrations, receptor function, receptor density and diffusion of cytoplasmic Ca2+. The rate of propagation of the Ca2+ wave is possibly dependent upon any of these processes. 

Patemain, A. V., Herrera, M. T Nieto, M. A., and Lerma, J. (2000) GluR5 and GluR6 kainate receptor subunits coexist in hippocampal neurons and coassemble to form functional receptors../. Neurosci. 20, 196-205. 

Sovago J, Dupuis DS, Gulyas B, Hall H. 2001. An overview on functional receptor autoradiography using [ SjGTPyS. Brain Res Rev 38 149-164. 

Barnard EA, MEedi R, Sumikawa K. 1982. Translational of exogenous messenger RNA coding for nicotinic acetylcholine receptors produces functional receptors in Xenopus oocytes. Proc R Soc Lond B 215 241. 

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