Recombinant production and characterization of the carbohydrate recognition domain from Atlantic salmon C-type lectin receptor C (SCLRC)

The Atlantic salmon C-type lectin receptor C (SCLRC) locus encodes a potential oligomeric type II receptor. C-type lectins recognize carbohydrates in a Ca2+-dependent manner through structurally conserved, yet functionally diverse, C-type lectin-like domains (CTLDs). Many conserved amino acids in animal CTLDs are present in SCLRC, with the notable exception of an asparagine crucially involved in Ca2+- and carbohydrate-binding, which is tyrosine in SCLRC. SCLRC also contains six cysteines that form three disulfide bonds. Although SCLRC was originally identified as an up-regulated transcript responding to Aeromonas salmonicida infection, the biological role of this protein is still unknown. To study the structure and ligand binding properties of SCLRC, we created a homology model of the 17 kDa CTLD and produced it as an affinity-tagged protein in the periplasm of Escherichia coli by co-expression of proteins that facilitate disulfide bond formation. The recombinant form of SCLRC was characterized by a protease protection assay, a solid-phase carbohydrate-binding assay, and frontal affinity chromatography. On the basis of this characterization, we classify SCLRC as a C-type lectin that binds to mannose and its derivatives.