Receptor/translocator protein

Fig. 16. Mitochondrial import of cholesterol. The StAR protein is the major cholesterol (CHOL) carrier bringing the lipid to import sites. The StAR protein is phosphorylated by cyclic AMP-dependent protein kinase (PKA) that is recruited to the mitochondria by the protein PAP7. PAP7 is a binding partner of the peripheral benzodiazepine receptor/translocator protein (TSPO), which forms a complex with the voltage-dependent anion channel (VDAC) and an adenine nucleotide transporter (ANT) at contact sites between the inner and outer mitochondrial membranes. The multiprotein complex constitutes a cholesterol transporter that moves cholesterol from StAR to the inner mitochondrial membrane where the side-chain cleavage enzyme (CYP-11 Al) converts it to pregnenolone (PREG).

An assay that produces multiple biological readouts. Most commonly used in relation to the mathematical analysis of an image acquired using an automated microscope whereby analysis algorithms quantify cellular parameters (e.g., number, motility, neurite outgrowth, size, shape) and subcellular events (e.g., receptor internalization, protein translocation, protein expression nuclei shape). 

The initial step after cellular uptake of T4 is metabolic transformation to 3,5,3, -tri-iodothyronine (T3) (Fig. 52-8), which interacts with cytosolic and nuclear receptors, as well as with synaptosomal membrane binding sites of unknown function [25], Cytosolic receptors are proteins of 70 kDa that do not appear to undergo translocation to cell nuclei, nor do they appear to be nuclear proteins that have leaked out of cell nuclei during cell rupture nuclear receptors are proteins of 50 70 kDa that have both DNA-and hormone-binding domains [25,26,28],... 

Lavin, A., Hahn, D., and Gasiewicz, T. A., Expression of functional aromatic hydrocarbon receptor and aromatic hydrocarbon nuclear translocator proteins in murine bone marrow stromal cells, Arch. Biochem. Biophys., 352, 9, 1998. 

In addition to the HECT domain, there is another domain in many E3s called the WW domain. The WW domain is thus named because of the characteristic tryptophan (W is the single letter code for the amino acid tryptophan) believed to be critical for protein-protein interaction. The WW domain-containing E3s also tend to have a C2 domain. The presence of C2 domain is highly relevant to nervous system function because C2 domain responds to the elevation of intracellular Ca and helps in translocation to the plasma membrane. Therefore, presence of this domain in neuronal HECT E3s might be critical in ligating ubiquitin to neurotransmitter receptors or proteins associated with them. 

Rodig SJ, Rutok IL, Paterson IC et al (2010) The pre-B-cell receptor associated protein VpreBS is a useful diagnostic marker for identifying c-MYC translocated lymphomas. Haematologica 95 2056-2062... 

Fig. 7.10. Functions and regulation of protein kinase C. Receptor-controlled signal pathways lead to formation of the intracellular messenger substances and diacylglycerol (DAG), that, like phorbol ester (TPA), activate protein kinase C (PKC). Translocation to the cell membrane is linked with activation of protein kinase C receptors for protein kinase C, the RACK proteins, are also involved. Substrates of protein kinase C are the MARCKS proteins and other proteins associated with the cytoskeleton. Other substrates are the Raf kinase (see Chapter 10) and the receptor for vitamin D3 (VDR, see Chapter 4).

Proteins, which have many physiological roles in normal cell function, are intimately associated with lipids and may be located throughout lipid bilayers. These proteins may be located on either the surface or traverse the entire structure. Hydrophobic forces are responsible for maintaining the structural integrity of proteins and lipids within membranes, but movement within the membranes may occur. External and internal membrane proteins can function as receptors. Many proteins that traverse the membrane are transport proteins, and are involved in translocation of ligands that is, they are involved in active and facilitated transport. 

Pollenz RS, Sattler CA, Poland A. 1994. The aryl hydrocarbon receptor and aryl hydrocarbon receptor nuclear translocator protein show distinct subcellular localizations in Hepa lclc7 cells by immunofluorescence microscopy. Mol Pharmacol 45 428-438. 

The mRNA for the secretory protein binds to a free cytoplasmic ribosome and protein synthesis begins. The first part of the protein made is the N-terminal signal peptide. A signal recognition particle (SRP), which is a complex of a 7S RNA and six proteins, binds to the signal peptide and stops further protein synthesis. This stops the secretory protein from being released prematurely into the cytosol. The ribosome-mRNA-SRP complex now binds to an SRP receptor, a protein on the surface of the ER. The ER membrane also contains a ribosome receptor protein associated with a protein translocator. In a concerted series of reactions, the ribosome is held tightly by the ribosome receptor protein, the SRP... 

Fig. 11.1 Activation of MAPK pathway by Angll and ET-1 in VSMC. Stimulation of Angll and ET-1 receptors through Gq/n activation enhances the activity of PLCp. Activated PLC 3 converts PIP2 to IP3 and diacylglycerol (DAG). IP3 elevates the concentration of intracellular calcium and DAG activates PKC. PKC and/or Ca2+/calmodulin (CaM)-dependent protein kinases (CaMK) activate nonreceptor (NR) and/or receptor (R) protein tyrosine kinases. Activation of these components signals the stimulation of Ras/Raf/MEK/ERKl/2 and p70 s6k. ERK1/2 and p70 s6k are translocated to nucleus and regulate nuclear events by activating transcription factors through phosphorylation.

Figure 12.6 Roles of signal recognition particles (SRP), SRP receptor (docking protein), ribosome binding proteins (ribophorin I and II), and signal peptidase in translocation of nascent polypeptide chains across ER membrane. AA, amino acids.

This section indicates that is possible to transfect cells with GFP fusion proteins of the AR families. The co-localization of these proteins with fluorescent ligands provides a link that allows comparison with native cell systems that do not possess such useful tags but that bind the fluorescent ligands. However, an additional utility is provided by the ability to label receptors in native systems with GFP, which provides the opportunity for receptor translocation studies in native cells. This has been accomplished on two levels. First, by in vitro transfection of native tissues or cells (see Fig. 1C) and second by creating transgenic mice harboring the GFP-AR constructs (see Chapter 7). 

ReyesH, Reisz-Porszasz S,HankinsonO. 1992. Identification of the Ah receptor nuclear translocator protein (Arnt) as a component of the DNA binding form of the Ah receptor. Science 256 1193-95... 

Probst MR, Reisz-Porszasz S, Agbunag RV, Ong MS, Hankinson O. 1993. Role of the aryl hydrocarbon receptor nuclear translocator protein in aryl hydrocarbon (dioxin) receptor action. Molec. Pharmacol. 44 511-18... 

Holmes JL, Pollenz RS. 1997. Determination of aryl hydrocarbon receptor nuclear translocator protein concentration and subcellular localization in hepatic and nonhepatic cell culture lines development of quantitative Western blotting protocols for calculation of aryl hydrocarbon receptor and aryl hydrocarbon receptor nuclear translocator protein in total cell lysates. Molec. Pharmacol. 52 202-11... 

Rowlands, J.C., I.L. McEwan and J.A. Gustafsson. Trans-activation by the human aryl hydrocarbon receptor and aryl hydrocarbon receptor nuclear translocator proteins direct interactions with basal transcription factors. Mol. Pharmacol. 50 538—548, 1996. 

Necela, B. and R.S. Pollenz. Identification of a novel C-terminal domain involved in the negative function of the rainbow trout Ah receptor nuclear translocator protein isoform a (rtARNTa) in Ah receptor-mediated signaling. Biochem. Pharmacol. 62 307—318, 2001. 

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