Herring antifreeze protein: primary structure and evidence for a C-type lectin evolutionary origin.

A complementary DNA (cDNA) for a type II antifreeze protein (AFP) was isolated from an Atlantic herring liver cDNA library and sequenced. The predicted protein sequence is homologous to those of the type II fish AFP from smelt and sea raven; it is also homologous to the carbohydrate recognition domains (CRD) of calcium-dependent (C-type) lectins and similar domains in lectin-like proteins. Herring belong to the infradivision Clupeomorpha, which is distinct from the Euteleostei to which all other AFP-producing fish belong. The occurrence of type II AFP in widely divergent fish groups and their homology to C-type lectin CRDs suggest that type II AFPs evolved from these lectins. Amino acid residues forming the hydrophobic cores of rat mannose-binding protein A (MBP-A) that are conserved in character among C-type lectins are also conserved in the herring AFP. The herring AFP also requires Ca2+ for thermal hysteresis activity. These results suggest that herring AFP is structurally and functionally similar to the CRDs of C-type lectins and related domains in other proteins.