Acceptor proteins

Clapp A.R., Mendintz I.L., Mauro J.M., Fisher B.R., Bawendi M.G., Mattoussi H. Fluorescence Resonance Energy Transfer Between Quantum Dot Donors and Dye-Labeled Protein Acceptors,./. Am. Chem. Soc. 2004 126 301-310. 

Free steroids that do not bind with plasma proteins enter target cells by passive diffusion and bind with cytoplasmic soluble-binding proteins (acceptor region), forming a steroid-protein complex. This enters the nucleus, where it interacts with steroid receptors on chromatin. 

Clapp, A. R., I. L. Medintz, J. M. Mauro, B. R. Fisher, M. G. Bawendi, and H. Mattoussi. Fluorescence resonance energy transfer between quantum dot donors and dye-labeled protein acceptors. J. Am. Chem. Soc. 126, 301-310 (2004). 

Enzymic transfer of D-xylose from uridine 5 -(D-xylopyranosyI-HC pyrophosphate) to L-serine residues of endogenous protein acceptors from (a) a cell tumor of the mouse188 and (b) chick-embryo cartilage189 occurs in cell-free extracts of both of these tissues, in the absence of biosynthesis of protein. The enzyme preparations employed were from the supernatant liquor, although activity was also present in the insoluble fractions. In these two types of tissue, the acceptors are heparin and chondroitin sulfate, respectively, but the presence of other D-xylose-containing glycoproteins in ascites fluid from... 

Coumarin (2H-l-benzopyran-2-one) is a known inhibitor of cellulose formation,355-357 and Hopp and coworkers358 found that, in membranes from the alga Prototheca zopfii, it inhibits the transfer in vitro of the lipid-linked cello-oligosaccharide to its protein acceptor (see Section II,2,b). 

Jump, D.B. and Smulson, M. (1980) Purification and characterization of the major non-histone protein acceptor for poly (adenosine diphosphate ribose) in HeLa cell nuclei. Biochemistry, 19, 1024-1030. 

Steroid receptors control gene expression in target cells. An understanding of the molecular interactions between receptors and specific nuclear components is crucial for elucidating the mechanism of hormone action. Receptor binding to at least three structural elements of nuclei has been described. These include the nuclear matrix, nucleoacidic chromatin proteins (acceptor proteins), and specific DNA sequences in 5 upstream elements of hormone responsive genes. 

UDPglucose + acceptor protein — acceptor protein-glucose + UDP... 

Ninety percent of the three-center hydrogen bonds formed by main-chain N-H groups involve at least one protein acceptor atom the other acceptor being either a water molecule (53%) or another protein atom (47%). With side-chain N-H groups, one half interact with water molecules, the other half with one or more protein acceptors. O... 

NADH-cytochrome f>o reductase (9) and NADPH-cytochrome P-450 reductase (10, 11) are microsomal enzymes. The latter has been referred to until very recently as NADPH-cytochrome c reductase, since that is how it is assayed, but there is no cytochrome c in microsomes and its physiological acceptor seems to be cytochrome P-460. It is thus distinguished from NADH-putidaredoxin reductase (12), NADPH-adrenodoxin reductase (13), and NADH-rubredoxin reductase (14). The adrenodoxin reductase and the rubredoxin reductase, together with their respective iron-sulfur protein acceptors, each constitute a cytochrome P-460 reductase system. 

A third species, Fx, the spectrum of which considerably deviates from that of a ferredoxin, is observed under highly reducing conditions [43,44], From Mossbauer studies it was calculated that Fx is a 4Fe-4S iron-sulfur protein [45], It is still not quite certain, however, whether under physiological conditions Fx really acts as an obligatory electron acceptor. In spite of the above-mentioned uncertainties, EPR is the only technique that is capable of furnishing detailed information on the various iron-sulfur protein acceptors their optical absorbance difference spectra all show a rather uninformative weak band around 430 nm,... 

The terminal phosphate group is the site of attachment of the achvated oligosaccharide, which is subsequently transferred to the protein acceptor. Dolichol phosphate resides in the ER membrane with its phosphate terminus on the cytoplasmic face. 

The general function of this complex is that of transferring electrons from ubiquinone (or plastoquinone) to a hydrophilic protein acceptor (cytochrome c or plastocyanin). Therefore, in bacterial photosynthesis, it catalyzes the recycling of electrons from the secondary electron acceptor (Qn) to the secondary electron donor (cyt. Cj), completing thereby the cyclic electron transfer system. In chloroplasts and cyanobacteria, an analogous system transfers the electrons from plastoquinone (the secondary acceptor of PSII, A, 3) to plastocyanin (the secondary donor to PSI, 0, 2) and provides in this way an intersystem redox connection between PSII and PSI. The same complex is also involved in the cycling of electrons around PSI. 

The G proteins are efficient PT substrates only in their trimeric forms, whereas isolated Ga monomers are much less well ADP-ribosylated (Katada et al., 1986). However, peptides composed of only the C-terminal residues of Ga may also be efficiently ADP-ribosylated by PT (Graf et al., 1992), suggesting that the C-terminal region of the full-length Ga may be relatively unavailable in the monomeric form. One of the regions of the SI subunit found to be involved in the interaction with the G protein acceptor substrates is the C-terminal portion of the enzyme. Deletion of this region results in a dramatic decrease of ADP-ribosylation efficiency, whereas binding to the donor substrate NAD"" and the catalytic rate are not affected (Locht etal., 1990 Cortina et al., 1991). 

Specific enzymes link the oligosaccharide units on proteins either to the side-chain oxygen atom of a serine or threonine residue or to the side-chain amide nitrogen atom of an asparagine residue. Protein gly-cosylation takes place in the lumen of the endoplasmic reticulum. The. hi-linked oligosaccharides are synthesized on dolichol phosphate and subsequently transferred to the protein acceptor. Additional sugars are attached in the Golgi complex to form diverse patterns. 

Two different enzymes degrade poly (ADP-ribose) and a third releases the remaining monomeric ADP-ribose from its attachment to the protein acceptor (Figure 2). 

Helmkamp (1980a) studied the effect of the fatty acid composition of the acceptor lipid on the stimulation of phosphatidylinositol transfer from rat liver microsomes to phosphatidylcholine vesicles by bovine brain exchange protein. Acceptor vesicles containing egg phosphatidylcholine or dioleoyl phosphatidylcholine gave approximately the same transfer activity, whereas dielaidoyl phosphatidylcholine or dimyristoyl phosphatidylcholine vesicles produced lower transfer rates. Zborowski and Demel (1982) used the same protein and measured the rate of transfer of phosphatidylinositol from a monolayer to phosphatidylcholine vesicles. Vesicles of egg, dioleoyl, dielaidoyl, and dipalmitoyl phosphatidylcholine, even below its phase transition temperature, all gave equivalent transfer rates. However, a reduced rate was found when dimyristoyl and dilin-oleoyl phosphatidylcholine, and other phosphatidylcholines with two polyunsaturated fatty acids, were used. Table IV shows a comparison of the transfer activities measured in the two assays. The transfer rates are expressed as a percent of the transfer rate obtained with egg phosphatidylcholine acceptor vesicles. 

Phosphoprotein phosphatases are responsible for the cleavage of phosphate groups from their protein acceptors. Some reports suggest that these enzymes can be inhibited by zinc. The actions of cAMP, then, can be seen to be terminated by two mechanisms the breakdown of cAMP by phosphodiesterase and the removal of phosphate groups from phosphoproteins by phosphatases. 

Wu, N., Cane, D.E. Khosla, C. Quantitative analysis of the relative contributions of donor acyl carrier proteins, acceptor ketosynthases, and linker regions to intermodular transfer of intermediates in hybrid polyketide synthases. Biochemistry 41, 5056-5066 (2002). 

Bacteria Protein acceptor Location of glycosylation glycosylation sites Reference(s)... 

Protein acceptor Oligosaccharyitransferase Locus expressing the desired Und-PP-giycan (i.e., O antigen)... 

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