Crosslinking of N-acetyllactosamine-containing glycoproteins to galectin-1 with an introduced cysteine using a photoactivatable sulfhydryl reagent

Relatively weak interactions between galectins and their potential ligands can hinder identification of physiological lectin ligands using conventional methods such as affinity purification. We have employed a combination of cysteine mutagenesis with chemical crosslinking using a photoactivatable sulfhydryl reagent benzophenone-4-maleimide to obtain a covalent complex between human galectin-1 and the model glycoprotein ligands asialofetuin and laminin which contain an N-acetyllactosamine structure. A crosslinked product was obtained only when galectin-1 with an introduced cysteine interacted with these glycoproteins via their carbohydrate moiety. This procedure should be useful for the detection of important, and as yet unidentified, ligands for galectins which cannot be currently detected because of their relatively weak interaction.