Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two lectin-resistant mutants derived from Madin Darby canine kidney cells, with constitutive alterations in the asparagine-linked carbohydrate moieties, retained the characteristic structural and functional epithelial polarity of the parental cells. A ricin-resistant cell line was unable to incorporate galactose-sialic acid into glycoproteins and, from the pattern of cross-resistance to other lectins, appears to be different from previously described lines resistant to this lectin: the mutation in a concanavalin A-resistant line results, probably, in the production of defective carbohydrate cores of glycoproteins. In spite of glycosylation defects which result in an increased electrophoretic mobility of many cellular glycoproteins, both mutants retained the typical asymmetric structure of the plasma membrane (microvilli on the apical surface, junctional elements on the basolateral surface), functional tight junctions, and unidirectional active transport of electrolytes and water. These results suggest that glycoproteins with terminal galactose-sialic acid moieties are not critically involved in the development and maintenance of polarity in epithelial cells. The mutant cells, particularly the ricin-resistant line, exhibited, however, morphological and electrophysiological changes which suggest a quantitative effect of the mutations on intracellular traffic of membranes and tight junction formation. The cell lines described in this paper, the first lectin-resistant mutants of epithelial lineage, should prove useful tools for studying the peculiarities of glycosylating pathways in polarized cells.
Mol Cell Biol 1982 Oct
PMID:Lectin-resistant mutants of polarized epithelial cells. 717 11

The alpha-sarcin loop of Escherichia coli 23S rRNA is a universally-conserved structure involved in the binding of elongation factors Tu and G and is the site of action of the ribosome-inactivating proteins (RIPs). One such group, the N-glycosidase RIPs, act by the removal of a single adenine residue (A2660) believed to exist in a GAGA-containing tetraloop structure. The action of two RIPs, the catalytic A-chain from the heterodimeric toxic lectin ricin (RTA) and the single-chain RIP pokeweed antiviral protein (PAP), which are known to be highly homologous in tertiary structure, was determined on native ribosomes or naked 23S rRNA containing mutations designed to affect the structure of the GAGA tetraloop. One such mutant rRNA containing G2663C, which abolishes the potential tetraloop by disrupting the Watson-Crick base-pair involved in closing it, resulted in a loss of depurination by RTA, but not by PAP. A similar result was observed for mutant G2661A. The double mutant C2658G + G2663C, which restores the tetraloop-closing base-pair but in the reverse orientation, resulted in sensitivity to both PAP and RTA, as in the wild-type. Thus, the tetraloop structure is required for the action of RTA, but not of PAP, and unlike RTA, PAP does not require G at position 2661. RNA containing the G2664C mutation, which lies outside the tetraloop, served as a substrate for both PAP and RTA. The comparison of the recognition elements for PAP and RTA was made with naked (deproteinised) rRNA, because RTA does not act on E. coli ribosomes. However, PAP is active on E. coli ribosomes, and it was found that the action of PAP on ribosomes containing the above mutations paralleled exactly that on the corresponding naked rRNAs. It is concluded that the recognition elements for PAP and RTA differ and may account, at least in part, for the fact that PAP but not RTA catalyses the depurination of E. coli ribosomes.
J Mol Biol 1995 Dec 15
PMID:The action of pokeweed antiviral protein and ricin A-chain on mutants in the alpha-sarcin loop of Escherichia coli 23S ribosomal RNA. 750 Mar 55

The N-terminal sequence of the three isoforms of gelonin is identical. Cyanogen bromide cleavage of gelonin produced fragments of Mr 17,000, 13,000, 11,000 and 7,000. The apparent Mr 17,000 component was identified as the N-terminal fragment and represents the major antigenic domain of the protein as it reacted with antibody to the native protein but this fragment did not inhibit protein synthesis in the in vitro translation assay. Our data may suggest possibilities for separation of antigenic and catalytic domains of this ribosome inactivating protein.
Biochem Mol Biol Int 1993 Nov
PMID:Structural characterization of gelonin: evidence for separate antigenic and cytotoxic domains. 750 82

The remarkable resistance of isolated ribosomes to gelonin is overcome by cofactors present in post-ribosomal supernatants. In rat liver post-ribosomal supernatant RNA is the cofactor responsible of the sensitization of ribosomes. Isolated RNA, which consists mostly of deacylated tRNA, accounts for less than 10 per cent of the activity of the original supernatant. The activity of the supernatant is completely destroyed by micrococcal nuclease and RNAase A and also by proteinase K, suggesting that some protein enhances the effect of RNA. RNA has a role also in the sensitization of ribosomes to alpha-sarcin, an RNAase which inactivates ribosomes by hydrolyzing a single phosphodiester bond in the same region of 28S rRNA which is the target of the N-glycosidase activity of gelonin.
Biochem Mol Biol Int 1994 Mar
PMID:RNA present in post-ribosomal supernatants makes ribosomes susceptible to inactivation by gelonin and alpha-sarcin. 751 79

A chimeric toxic protein was prepared from the mistletoe lectin I A-chain and ricin B-chain by using the disulfide exchange reaction. Ricin and chimeric protein were indistinguishable in binding to immobilized asialofetuin in ELISA. The chimeric protein was more toxic for Jurkat cells than native mistletoe lectin I, but not as effective as native ricin. In the presence of NH4Cl, which enhances the toxicity of some toxins and immunotoxins, but does not influence ricin toxicity, both ricin and chimeric toxin had equal cytotoxic activity. The possibility is discussed that the ricin B-chain protects the ricin A-chain from degradation during delivery from the cell surface to the place where it is translocated into the cytosol.
Mol Biol (Mosk)
PMID:[Chimeric toxin of the A-subunit of viscumin and the B-subunit of ricin]. 751 22

The goal of this study was to exploit molecular recognition of cell surface receptors by viral surface glycoproteins as a means for the selective intracellular delivery of macromolecules. To accomplish this, artificial viral envelopes (AVE) resembling the human immunodeficiency virus-1 (HIV-1) were designed as a model system. Recombinant HIV-1 surface glycoprotein gp160 (HIV-1 rgp160) was inserted in the artificial envelope by a two-step detergent dialysis process. The artificial HIV-1 envelope recognized the CD4 cell surface receptor. FITC-dextran and ricin A were employed as model macromolecules as they cannot passively diffuse across cell membranes. Selective transfer of FITC-dextran encapsulated in HIV-1 rgp160 AVE into a CD4-positive cell line (REX-1B) versus a CD4-negative cell line (KG-1) was demonstrated. Ricin A at concentrations as low as 2 ng/ml arrested cell growth of CD4-positive MOLT-4 cells, whereas 8 ng/ml ricin A in solution had no effect on cell growth. The arrest of cell growth was reverted in the presence of excess anti-gp120 monoclonal antibody. Naked envelopes (without HIV-1 rgp160 inserted) were also found to interact with cells and transfer material, although less efficiently and in a non-specific manner. Viral mimicry using AVE may be a means for targeted intracellular delivery of peptides, proteins, enzymes, toxins, oligodeoxynucleotides, gene constructs, and other non-diffusive, labile or toxic macromolecules.
J Mol Recognit
PMID:(Patho)physiologic pathways to drug targeting: artificial viral envelopes. 754 Dec 29

Ricin is an RNA N-glycosidase that hydrolyzes a single adenine base from a conserved loop of 28S ribosomal RNA, thus inactivating protein synthesis. Molecular-dynamics simulation methods are used to analyze the structural interactions and thermodynamics that govern the binding of formycin 5'-monophosphate (FMP) and several of its analogs to the active site of ricin A-chain. Simulations are carried out initiated from the X-ray crystal structure of the ricin-FMP complex with the ligand modeled as a dianion, monoanion and zwitterion. Relative changes in binding free energies are estimated for FMP analogs constructed from amino substitutions at the 2- and 2'-positions, and from hydroxyl substitution at the 2'-position.
J Comput Aided Mol Des 1995 Jun
PMID:Simulation analysis of formycin 5'-monophosphate analog substrates in the ricin A-chain active site. 756 75

The crystal structure of abrin-a, a type II ribosome-inactivating protein from the seeds of Abrus precatorius, has been determined from a novel crystalline form by the molecular replacement method using the coordinates of ricin. The structure has been refined at 2.14 A to a R-factor of 18.9%. The root-mean-square deviations of bond lengths and angles from the standard values are 0.013 A and 1.82 degrees, respectively. The overall protein folding is similar to that of ricin, but there are differences in the secondary structure, mostly of the A-chain. Several parts of the molecular surface differ significantly; some of them are quite near the active site cleft, and probably influence ribosome recognition. The positions of invariant active site residues remain the same, except the position of Tyr74. Two water molecules of hydrogen-bonded active site residues have been located in the active site cleft. Both of them may be responsible for hydrolyzing the N-C glycosidic bond. The current abrin-a structure is lactose free; this is probably essential for abrin-a crystallization. The B-chain is a glycoprotein, and the positions of several sugar residues of two sugar chains linked to earlier predicted glycosylation sites were determined. One of the sugar chains is a bridge between two neighboring molecules, since one of its mannose residues is connected to the galactose binding site of the neighboring molecule. Another sugar chain covers the surface of the B-chain.
J Mol Biol 1995 Jul 14
PMID:Crystal structure of abrin-a at 2.14 A. 760 80

Gelonin is a single chain ribosome inactivating protein (RIP) with potential application in the treatment of cancer and AIDS. Diffraction quality crystals grown using PEG3350, belong to the space group P21, with a = 49.4 A, b = 44.9 A, c = 137.4 A and beta = 98.4 degrees, and contain two molecules in the asymmetric unit. Diffraction data collected to 1.8 A resolution has a Rm value of 7.3%. Structure of gelonin has been solved by the molecular replacement method, using ricin A chain as the search model. Crystallographic refinement using X-PLOR resulted in a model for which the r.m.s deviations from ideal bond lengths and bond angles are 0.012 A and 2.7 degrees, respectively. The final R-factor is 18.4% for 39,806 reflections for which I > 1.0 sigma (I). The C alpha atoms of the two molecules in the asymmetric unit superpose to within 0.38 A for 247 atom pairs. The overall fold of gelonin is similar to that of other RIPs such as ricin A chain and alpha-momorcharin, the r.m.s.d. for C alpha superpositions being 1.3 and 1.4 A, respectively. The catalytic residues (Glu166, Arg169 and Tyr113) in the active site form a hydrogen bond scheme similar to that observed in other RIPs. The conformation of Tyr74 in the active site, however, is significantly different from that in alpha-momorcharin. Three well defined water molecules are located in the active site cavity, and one of them, X319, superposes to within 0.2 A of a corresponding water molecule in the structure of alpha-momorcharin. Any of the three could be the substrate water molecule in the hydrolysis reaction catalysed by gelonin. Difference electron density for a N-linked sugar moiety has been observed near only one of the two potential glycosylation sites in the sequence. The amino acid at position 239 has been established as Lys by calculation of omit electron density maps. The two cysteine residues in the sequence, Cys44 and Cys50, form a disulphide bond, and are therefore not available for disulphide conjugation with antibodies. Based on the structure, the region of the molecule that is involved in intradimer interactions is suggested to be suitable for introducing a Cys residue for purposes of conjugation with an antibody to produce useful immunotoxins.
J Mol Biol 1995 Jul 14
PMID:X-ray structure of gelonin at 1.8 A resolution. 760 81

A computer model of dianthin 30, a type 1 ribosome-inactivating protein (RIP), is constructed by homology modeling using two known X-ray structures; a type 1 RIP, pokeweed antiviral protein (PAP), and chain A of a type 2 RIP, ricin. The 3D structure is refined by molecular dynamics and its binding site compared with those of PAP and ricin using molecular electrostatic potential mapping. The differences in the maps obtained clearly show how, despite the similarity of the topology of the binding site, differences in electrostatic potential can account for the experimentally observed differences in substrate recognition and binding. This demonstrates the potential of these techniques for guiding further experimental analyses.
J Mol Graph 1995 Apr
PMID:Substrate recognition by ribosome-inactivating protein studied by molecular modeling and molecular electrostatic potentials. 761 90


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