INTRODUCTION OF SELECTIN-LIKE BINDING-SPECIFICITY INTO A HOMOLOGOUS MANNOSE-BINDING PROTEIN

The structures of the ligand-binding C-type carbohydrate-recognition d omains of selectin cell adhesion molecules and of mannose-binding prot eins (MBPs) are similar to each other even though these proteins bind very different carbohydrate ligands. Our current understanding of liga nd binding by E-selectin is based on structural studies of unliganded E-selectin and of MBP-carbohydrate complexes, combined with results fr om mutagenesis of E-selectin. Five regions of E-selectin that differ i n sequence from the corresponding regions of MBP have been introduced into the carbohydrate-recognition domain of MBP. Four of the changes h ave little effect on ligand binding. Insertion of one stretch of posit ively charged amino acids alters the sugar binding selectivity of the domain so that it now binds HL-60 cells and serum albumin derivatized with sialyl-Lewis(x) tetrasaccharide, thus mimicking the properties of E-selectin.