title: Spectroscopical studies on the structural organization of the lectin discoidin I: analysis of sugar- and calcium-binding activities.
abstract: One of the common characteristics observed in different families of sugar-binding proteins is the presence of aromatic residues in the proximity of the functional sugar-binding site (Quiocho, F. (1986) Annu. Rev. Biochem. 55, 287-315). This general property has made these proteins a very appropriate subject for studies using intrinsic fluorescence assays. In the present report we have studied the sugar binding activity of the lectin discoidin I, using a fluorescence-monitored titration assay. The galactose binding has been estimated, with an affinity constant of 1.8.10(-7) M-1 in the absence of calcium. In the presence of 1 mM Ca2+, the Kd of galactose binding is lowered to 2.7.10(-8) M-1. Calcium binding, by itself, seems to occur as two components with Kd values of 10(-7) and 10(-6) M-1. From these data, and sequence comparison of discoidin I with other lectins, a general model for ligand binding has been proposed in which a sequence from position 176 to 188, together with another region close to an apolar tryptophan residue, most probably Trp-50, would participate in the calcium- and sugar-binding site(s) of this protein.
authors.affiliation: Instituto de Investigaciones Biomédicas, Facultad de Medicina, Universidad Autónoma de Madrid, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Valencia
authors.forename: A
authors.initials: A
authors.lastname: Pestaña
authors.forename: A
authors.initials: A
authors.lastname: Cano
mesh_terms: D000116:Acetylgalactosamine / Q000378:metabolism; D000117:Acetylglucosamine / Q000378:metabolism; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D050260:Carbohydrate Metabolism; D004023:Dictyostelium / Q000032:analysis*; D000070821:Discoidins; D005656:Fungal Proteins / Q000378:metabolism*; D005690:Galactose / Q000378:metabolism; D037102:Lectins / Q000378:metabolism; D015800:Protozoan Proteins; D013050:Spectrometry, Fluorescence
chemical_list: D000070821:Discoidins; D005656:Fungal Proteins; D037102:Lectins; D015800:Protozoan Proteins; D000116:Acetylgalactosamine; D002118:Calcium; D000117:Acetylglucosamine; D005690:Galactose