Studies on the molecular recognition of synthetic methyl β-lactoside analogs by ricin, a cytotoxic plant lectin

Authors

  • Alfonso RIVERA-SAGREDO,

    1. Grupo de Carbohidratos, Institute de Quimica Orgánica, Consejo Superior de Investigaciones Cientificas, Madrid, Spain
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  • Dolores SOLIS,

    1. Instituto de Quimica Fisica ‘Rocasolano’, Consejo Superior de Investigaciones Cientificas, Madrid, Spain
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  • Teresa DIAZ-MAURIÑO,

    1. Instituto de Quimica Fisica ‘Rocasolano’, Consejo Superior de Investigaciones Cientificas, Madrid, Spain
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  • Jesús JIMENEZ-BARBERO,

    Corresponding author
    1. Grupo de Carbohidratos, Institute de Quimica Orgánica, Consejo Superior de Investigaciones Cientificas, Madrid, Spain
      Correspondence to M. Martin-Lomas and J. Jiménez-Barbero, Grupo de Carbohidratos, Instituto de Quimica Orgánica, C.S.I.C., Juan de la Cierva 3, E-28006 Madrid, Spain
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  • Manuel MARTIN-LOMAS

    Corresponding author
    1. Grupo de Carbohidratos, Institute de Quimica Orgánica, Consejo Superior de Investigaciones Cientificas, Madrid, Spain
      Correspondence to M. Martin-Lomas and J. Jiménez-Barbero, Grupo de Carbohidratos, Instituto de Quimica Orgánica, C.S.I.C., Juan de la Cierva 3, E-28006 Madrid, Spain
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Correspondence to M. Martin-Lomas and J. Jiménez-Barbero, Grupo de Carbohidratos, Instituto de Quimica Orgánica, C.S.I.C., Juan de la Cierva 3, E-28006 Madrid, Spain

Abstract

The binding of methyl β-lactoside and of all possible monodeoxy derivatives of methyl β-lactoside to the galactose-specific highly cytotoxin lectin ricin, has been investigated. The distribution of low-energy conformers of the disaccharide structures has been first determined using molecular-mechanics calculations and high-resolution NMR spectroscopy. The nuclear Overhauser enhancements and specific deshieldings observed are in agreement with a similar distribution of low-energy conformers for all studied compounds which may be described by a major conformer defined by φ (H1′-C1′-O1′-C4) and Ψ (C1′-O1′-C4-H4) torsion angles of 49° and 5°, respectively, with contribution of conformers with angles φ/Ψ 24°/– 59°, 22°/– 32° and 6°/– 44°. Assuming that the disaccharides bind to the lectin in these preferred conformations, the apparent dissociation constants for the ricin-disaccharide complexes have been interpreted in terms of specific polar and nonpolar interactions. In agreement with X-ray data, the hydroxyl groups at positions 3, 4 and 6 of the β-d-galactopyranose moiety appear as key polar groups in the interaction with ricin. These results are in contrast to previous results which have established that position 6 is not involved in lectin binding. An important nonpolar interaction involving position 3 of the β-d-glucopyranose moiety, seems to be operative. The distribution of low-energy conformers of these disaccharide structures permits this interaction to take place with the hydroxyl group at this position intramolecularly bonded, thus rendering this region of the molecule more lipophylic in character for acceptance into nonpolar regions of the combining site.

Enzyme
 

Lactoperoxidase (EC 1.11.1.7)

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