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

Area of Science:

• Molecular Biology
• Evolutionary Biology
• Biochemistry

Background:

• Antifreeze proteins (AFPs) are crucial for fish survival in cold environments.
• Type II AFPs are found in various fish species, but their evolutionary origins remain debated.
• Atlantic herring (Clupeomorpha) are evolutionarily distinct from other known AFP-producing fish (Euteleostei).

Purpose of the Study:

• To isolate and characterize a type II antifreeze protein (AFP) from Atlantic herring.
• To investigate the evolutionary relationship between type II AFPs and other protein families.
• To determine the functional and structural properties of herring AFP.

Main Methods:

• Isolation and sequencing of a complementary DNA (cDNA) encoding type II AFP from an Atlantic herring liver cDNA library.
• Bioinformatic analysis to compare the herring AFP sequence with known proteins, including C-type lectins.
• Biochemical assays to assess the calcium dependence and thermal hysteresis activity of the herring AFP.

Main Results:

• A type II AFP complementary DNA (cDNA) was successfully isolated and sequenced from Atlantic herring.
• The herring AFP sequence showed significant homology to type II fish AFPs and to carbohydrate recognition domains (CRDs) of calcium-dependent (C-type) lectins.
• Herring AFP demonstrated a requirement for Ca2+ for its thermal hysteresis activity, similar to C-type lectins.

Conclusions:

• Type II antifreeze proteins (AFPs) likely evolved from C-type lectins, as evidenced by homologous domains and conserved residues.
• The presence of type II AFP in the evolutionarily distinct herring suggests a broader evolutionary origin for these proteins.
• Herring AFP functions similarly to the carbohydrate recognition domains of C-type lectins, requiring calcium for activity.