X-ray crystal structure of the human dimeric S-Lac lectin, L-14-II, in complex with lactose at 2.9-A resolution.

Abstract

S-Lac lectins are a family of soluble lactose-binding animal lectins, some of which have been implicated in modulating cell-cell and cell-matrix interactions through specific carbohydrate-mediated recognition.W e report here the x-ray crystal StNCtUre of a representative member of this family, the human dime5ic S-Lac lectin, L-14-11, in complex with lactose, at 2.9-A resolution.The two-fold symmetric dimer is made up of two extended anti-parallel P-sheets, which associate in a P-sandwich motif.Remarkably, the L-14-11 monomer shares not only the same topology, but a very similar P-sheet structure with that of the leguminous plant lectins, suggesting a conserved structure-function relationship.Carbohydrate binding by L-14-11 was found to involve protein residues that are very highly conserved among all S-Lac lectins.These residues map to a single DNA exon, suggesting a carbohydrate binding cassette common to all S-Lac lectins.