Receptors sequential types

The ion channel receptors are multi-subunit proteins which may be either homomeric (made up of multiple copies of a single type of subunit) or heteromeric (composed of more than one subunit type). These subunits come together after synthesis in the endoplasmic reticulum to form the mature receptor. Notice that stoichiometry is denoted by a subscript number. A receptor composed of two a and three /I subunits is therefore denoted as having a stoichiometry of This can cause confusion when related subunits are given sequential numbers /II, j]2, 3, etc. The convention is therefore that subunits are numbered normally while stoichiometry is indicated by subscripts so that a pentamer of a4 and j33 subunits might have a stoichiometry of a42/133. 

Another major protein component of clathrin-coated vesicles, generally known as adaptins, bind and link clathrin coats to the membrane [5], Multiple types of adaptins have been described, each type binding a unique set of cargo receptors and associated to a specific membrane organelle. Different sets of adaptins participate in forming the coat assembly complexes for the Golgi (API) and the plasma membrane (AP2). Sequential assembly and... 

The FhuA receptor of E. coli transports the hydroxamate-type siderophore ferrichrome (see Figure 9), the structural similar antibiotic albomycin and the antibiotic rifamycin CGP 4832. Likewise, FepA is the receptor for the catechol-type siderophore enterobactin. As monomeric proteins, both receptors consist of a hollow, elliptical-shaped, channel-like 22-stranded, antiparallel (3-barrel, which is formed by the large C-terminal domain. A number of strands extend far beyond the lipid bilayer into the extracellular space. The strands are connected sequentially using short turns on the periplasmic side, and long loops on the extracellular side of the barrel. 

Padwa et al. (187,188) concisely summarized his domino cycloaddition/ A -acyliminium ion cyclization cascade process, which involves sequentially the generation of an isomiinchnone 1,3-dipole, intramolecular 1,3-dipolar cycloaddition reaction, 77-acyliminium ion formation, and, hnally, Mannich cyclization. Kappe and co-workers (189) utilized Padwa s cyclization-cycloaddition cascade methodology to construct several rigid compounds that mimic the putative receptor-bound conformation of dihydropyridine-type calcium channel modulators. 

FIGURE 23.7 Dopamine (DA) is synthesized within neuronal terminals from the precursor tyrosine by the sequential actions of the enzymes tyrosine hydroxylase, producing the intermediary L-dihydroxyphenylalanine (Dopa), and aromatic L-amino acid decarboxylase. In the terminal, dopamine is transported into storage vesicles by a transporter protein (T) associated with the vesicular membrane. Release, triggered by depolarization and entry of Ca2+, allows dopamine to act on postsynaptic dopamine receptors (DAR). Several distinct types of dopamine receptors are present in the brain, and the differential actions of dopamine on postsynaptic targets bearing different types of dopamine receptors have important implications for the function of neural circuits. The actions of dopamine are terminated by the sequential actions of the enzymes catechol-O-methyl-transferase (COMT) and monoamine oxidase (MAO), or by reuptake of dopamine into the terminal. 

Fig. 5.2 Early G-protein signaling events at the AT]R. Phospholipases C and D are sequentially activated by heterotrimeric G-protein subunits to produce important second messengers such as IP3 and DAG. See text for details. ATiR, angiotensin II type 1 receptor DAG, diacylglycerol IP3, inositol 1,4,5-trisphosphate PA, phosphatidic acid PC, phosphatidylcholine PIP2, phosphatidylinositol-4,5-bisphosphate PKC, protein kinase C PLC, phospholipase C PLD, phospholipase D.

Van der Poll T, Malefyt RW, Coyle SM, Lowry SF. Antiinflammatory cytokine responses during chnical sepsis and experimental endotoxemia Sequential measurements of plasma soluble interleukin (IL)-1 receptor type II, IL-10, IL-13. J Infect Dis 1997 175 118-122. 

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