Binding and Uptake of the Toxic Lectins Abrin and Ricin by Mammalian Cells

Olsnes, Sjur; Sandvig, Kirsten; Refsnes, Karin; Fodstad, Øystein; Pihl, Alexander

doi:10.1007/978-1-4684-2772-1_13

Cited by 7 publications

(12 citation statements)

References 22 publications

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“…Since we have found earlier that the toxic effect is determined by the amount of toxin bound to the cells [6,7], the inhibition of protein synthesis by abrin at different cell densities was measured. In agreement with the results above, it was found ( fig.3), that a 3-4-times higher concentration of abrin is necessary to give 50% inhibition of protein synthesis when the cell density is raised from 5.…”

Section: Resultsmentioning

confidence: 99%

Cell density affects the binding of the toxic lectin abrin to HeLa cells in monolayer cultures

Sandvig

1978

FEBS Letters

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Section: Resultsmentioning

confidence: 99%

Cell density affects the binding of the toxic lectin abrin to HeLa cells in monolayer cultures

Sandvig

1978

FEBS Letters

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“…Olsnes and co-workers [4] observed that the time to achieve 50% inhibition of protein synthesis by ricin and abrin in HeLa cell is proportional to the reciprocal of the square root of the number of bound toxins. Assuming that the toxin binding is a linear function of concentrations added to the cell culture medium in the concentration range used, we have plotted the lag times as a function of inverse of the square root of toxin concentrations.…”

Section: Rate Of Protein Synthesis Inhibition In Thymocytementioning

confidence: 99%

“…A detailed study by Olsnes and co-workers [4] revealed that the length of the lag depends on the concentration of the toxin at certain concentration range and attains a constant time period at excess toxin concentration. Olsnes et al [4] also differentiated these two phases of the lag into a minimum lag (concentration independent) pertaining to the time for toxin entry into the cytosol and a concentration-dependent lag, at limiting concentrations of toxin, which supposedly corresponds to a first-order processing event prior to the first-order inactivation of protein synthesis. Based on the observation that the concentration-dependent lag period decreases in high pH and increases in low pH, Esworthy and Neville [5] proposed a pH-dependent chemical or enzymic processing event that governs the dose-dependent lag time.…”

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confidence: 99%

“…The inhibition of protein synthesis studied in cells in v i m is charac-terized by a monoexponential decrease in the radioactiveamino-acid incorporation following a period of no measurable intoxication, or a lag period [4].…”

mentioning

confidence: 99%

“…To account for the observed difference in the dose-dependent lag times, functional and structural variables of the toxins such as receptor-binding efficiency of B subunit and low-pH-induced structural alterations; a possible step that the toxin may encounter in the low-pH endosomal compartments, are measured and compared. Reduction of the disulfide bridge that connects the A and B subunits constitutes an obligatory step in the intoxication process [4]. Kinetics of intersubunit disulfide reduction in the four toxins are determined under a variety of conditions and its possible causal relationship with the observed difference in the dose-dependent lag period is investigated.…”

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The variants of the protein toxins abrin and ricin

Hegde

Karande

Podder

1993

European Journal of Biochemistry

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Kinetic data on inhibition of protein synthesis in thymocyte by three abrins and ricin have been obtained. The intrinsic efficiencies of A chains of four toxins to inactivate ribosomes, as analyzed by k,-versus-concentration plots were abrin 11, 111 > ricin > abrin I. The lag times were 90, 66, 75 and 105 min at a 0.0744 nM concentration of each of abrin I, 11, 111 and ricin, respectively. To account for the observed differences in the dose-dependent lag time, functional and structural variables of toxins such as binding efficiency of B chains to receptors and low-pH-induced structural alterations have been analyzed. The association constants obtained by stopped flow studies showed that abrin-I (4.13 X 1O'M-I s-]) association with putative receptor (4-methylumbelliferyI-a-~-galactoside) is nearly two times more often than abrin 111 (2.6X 105M-' s-') at 20°C. Equilibrium binding constants of abrin I and I1 to thymocyte at 37°C were 2.26 X lo7 M-' and 2.8 X 107 M ' respectively. pH-induced structural alterations as studied by a parallel enhancement in 8-anilino-L-naphthalene sulfonate fluorescence revealed a high degree of qualitative similarity. These results taken with a nearly identical concentration-independent lag time (minimum lag of 41 -42 min) indicated that the binding efficiencies and internalization efficiencies of these toxins are the same and that the observed difference in the dose-dependent lag time is causally related to the proposed processing event. The rates of reduction of inter-subunit disulfide bond, an obligatory step in the intoxication process, have been measured and compared under a variety of conditions. Intersubunit disulfide reduction of abrin I is fourfold faster than that of abrin I1 at pH 7.2. The rate of disulfide reduction in abrin I could be decreased 11-fold by adding lactose, compared to that without lactose. The observed differences in the efficiencies of A chains, the dose-dependent lag period, the modulating effect of lactose on the rates of disulfide reduction and similarity in binding properties make the variants a valuable tool to probe the processing events in toxin transport in detail.The phytotoxins abrin and r i c h contain two different subunits that play distinct roles in the potent cytotoxicities of the proteins [ 11. The B subunit. which contains two galactose-binding sites, binds cell surface glycoproteins and glycolipids containing terminal galactose and facilitates the entry of toxic A chain into the cytosol [ l , 21. The A subunit is an enzyme that depurinates a single base, adenine 4324, of the 28s rRNA thereby inactivating protein synthesis [3]. The action of these toxins on eucaryotic cells thus involves a minimum of three sequential steps; binding to plasma-membrane receptors by the B-chain, transmembrane transport of the whole toxin or the toxic chain into the cytosol and inactivation of protein synthesis by the catalytic A chain. The first and last steps have been studied in detail but the mechanism underlying toxin transport remains a puzzle.There ha...

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Properties and action mechanism of the toxic lectin modeccin: Interaction with cell lines resistant to modeccin, abrin, and ricin

Olsnes

Sandvig²,

Eiklid

et al. 1978

J Supramol Struct

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The toxic lectin modeccin, which inhibits protein synthesis in eukaryotic cells, is cleaved upon treatment with 2-mercaptoethanol into two peptide chains which move in polyacrylamide gels at rates corresponding to molecular weights 28,000 and 38,000. After reduction, the toxin loses its effect on cells, while its ability to inhibit cell-free protein synthesis increases. Like abrin and ricin it inhibits protein synthesis by inactivating the 60S ribosomal subunits. Modeccin binds to surface receptors containing terminal galactose residues. Competition experiments with various glycoproteins indicate that the modeccin receptors are different from the abrin receptors. In addition, they were present on HeLa cells in much smaller numbers. Moreover, mutant lines resistant to abrin and ricin were not resistant to modeccin and vice-versa. The toxin resistance of various mutant cell lines could not be accounted for by a reduced number of binding sites on cells. The data are consistent with the view that the cells possess different populations of binding sites with differences in ability to facilitate the uptake of the toxins and that in the resistant lines the most active receptors have been reduced or eliminated.

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Binding and Uptake of the Toxic Lectins Abrin and Ricin by Mammalian Cells

Cited by 7 publications

References 22 publications

Cell density affects the binding of the toxic lectin abrin to HeLa cells in monolayer cultures

Cell density affects the binding of the toxic lectin abrin to HeLa cells in monolayer cultures

The variants of the protein toxins abrin and ricin

Properties and action mechanism of the toxic lectin modeccin: Interaction with cell lines resistant to modeccin, abrin, and ricin

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