Molecular Characterization and Evolution of a Ficolin in the Primitive Fish, Acipenser baerii

Abstract

Ficolins are structurally and functionally homologous to MBL and can activate the lectin pathway of the complement cascade in mammals, however, nothing is known about the molecular identity of ficolins in teleosts. Here, we report the first identification of a ficolin gene in a primitive chondrostean sturgeon, Acipenser baerii, enabling investigation of its molecular characterization, evolutionary dynamics, and functional attributes. Nucleotide sequence of the identified A. baerii ficolin (AbFCN) comprised 3,439 bp with open reading frame (ORF) 963, encoding 320 amino acid residues protein, consisting of a signal peptide (Met1―Cys25), a collagen-like domain (Leu47―Asn111) and two cysteine residues (Cys269―Cys282) within a C terminal fibrinogen binding domain (Arg121―Phe320). Multiple sequence alignment and phylogenetic analysis revealed that AbFCN had high sequence similarity (>50%) with mammalian ficolins and shared ancestor within human FCN-3. RT-qPCR analysis of tissue distribution showed the highest expression in the liver and lowest expression in the heart. Collectively, this study provides the first molecular identity of the prototype ficolin in teleost and enhances our understanding of ficolin’s roles in teleost. Further research will explore in-depth functional study.