The N-terminal lectin domain (Nh) of the tandem repeat-type nematode galectin LEG-1 has a lower affinity for sugars than the C-terminal lectin domain. To confirm that LEG-1 forms a complex with N-acetyllactosamine-containing glycoproteins, we used several mutants of LEG-1 in which a unique cysteine residue was introduced into the Nh domain and examined their binding to bovine asialofetuin with a photoactivatable sulfhydryl crosslinking reagent. A crosslinked product was formed with the Q38C mutant, strongly suggesting the low-affinity interaction of Nh with the glycoprotein could be detected with this system. (c) 2006 Elsevier Inc. All rights reserved.