DYNAMICS OF THE LENS-CULINARIS AGGLUTININ-LACTOTRANSFERRIN AND SEROTRANSFERRIN COMPLEXES, FOLLOWED BY FLUORESCENCE INTENSITY QUENCHING OF FLUORESCEIN (FITC) WITH IODIDE AND TEMPERATURE

Dynamics of the fluorescent Lens culinaris agglutinin-fluorescein comp lex (LCA-FITC) are studied in absence and in presence of two glycoprot eins, lactotransferrin (LTF) and serotransferrin (STF). Glycans of the serotransferrin are not fucosylated, while those of the lactotransfer rin have an alpha-1,6-fucose bound to the N-acetylglucosamine residue linked to the peptide chain, and an alpha-1,3-fucose bound to the N-ac etyllactosamine residues. Interaction between the lectin and the two g lycoproteins occurs via the carbohydrate residues. Affinity between LC A and LTF is 50 times higher than that between LCA and STF, as a resul t of the alpha-1,6-fucose-LCA linkage. In the present work, we studied the effect of the tight bond between the alpha-1,6-fucose and LCA on the dynamics of the amino acids of the lectin, by fluorescence intensi ty quenching with iodide and by thermal intensity quenching. Fluoresce nce intensity quenching with iodide indicates that the bimolecular dif fusion constant of iodide is 2.402 +/- 0.068 x 10(9) and 1.160 +/- 0.0 90 x 10(9) M-1 s(-1), when the interaction occurs with free fluorescei n and with fluorescein bound to LCA, respectively. Binding of STF or L TF to the LCA-FITC complex yields a bimolecular diffusion constant of 1.675 +/- 0.06 x 10(9) and 1.155 +/- 0.087 x 10(9) M-1 s(-1), respecti vely. Thermal intensity quenching does not occur for fluorescein free in solution while it is linear with temperature with a relative change of 0.656%, 0.889% and 0.488% for FITC-LCA, FITC-LCA-LTF and FITC-LCA- STF complexes, respectively. Fluorescence intensity quenching with iod ide and thermal quenching experiments indicate that the dynamics of LC A increase as the result of the flexibility of the carbohydrate residu es (case of STF-LCA complex), and the presence of the a-1,6-fucose inh ibits the effect of the other carbohydrate residues as the result of t he tight bond that exists between the fucose and the lectin (case of L TF-LCA complex). (C) 1998 Elsevier Science B.V. All rights reserved.