Characterization and bacterial-binding activity of a novel C-type lectin from the red-spotted grouper, Epinephelus akaara

Because of their specific binding to carbohydrates, lectins play a crucial role in pathogen recognition and clearance in vertebrate animals. Previously, only two types of collectins had been isolated from bony fish: mannan-binding lectin (MBL) and galactose-binding lectin (GalBL). We sequenced a novel collectin (designated EALec1) from the red-spotted grouper, Epinephelus akaara. The gene structure of EALec1 and the alignment of the carbohydrate recognition domain of the three collectins demonstrated that EALec1 is a new type of collectin derived from MBL. We examined the expression pattern of the EALec1 transcripts in 12 tissues of the red-spotted grouper. The EALec1 gene was found to have multiple copies; their transcripts were detected in all 12 tissues. EALec1 was also recombined and expressed in Escherichia coli to investigate its immune functions and carbohydrate-binding characterization. We concluded that EALec1 belongs to the mannan-binding lectin group, despite its different Ca2+-dependent sites in the carbohydrate recognition domain, and that it is involved in the recognition and clearance of invaders in the red-spotted grouper.