Ficolin-2 (L-ficolin)

Ficolin-2, also known as L-ficolin, is synthesized in the liver and secreted into the bloodstream in humans and it is one of the major pattern recognition molecules of plasma/serum. Ficolin-2 has been localized to chromosome 9 (9q34) and contains 288 amino acids producing a 35Kd protein after glycosylation. It is composed of a short N-terminal region implicated in multimer generation, and a collagen-like domain consist of a series of 19 (Gly-X-Y) repeats. Generally, the distribution of serum ficolin-2 is perfectly Gaussian in healthy adult individuals, thus the mean and median are the same. The value has been demonstrated to be between 3 and 4 µg/mL.

It is worth noting that ficolin-2 is one of the few molecules known to activate the lectin pathway of complement activation. The activation is arisen after producing a complex with MBL-associated serine proteases (MASP)-1, -2, and -3. MASP-2 is an important protein for complement activation and its binding takes place at a site on the collagen-like region. Ficolin-2-MASP-2 interaction results in activation of the latter, enabling it to cleave complement components C2 and C4 like the C1q, r, s complex of the classical pathway stated by antigen-antibody formation. L-ficolin has been reported to bind to the Salmonella typhimurium (Ra strain), Pseudomonas aeruginosa, Gram-negative bacteria, Gram-positive species, Escherichia coli, as well as the Staphylococcus aureus and streptococci. Besides, all interactions were partially sensitive to GlcNAc.

Fig. 1 L-ficolin structure.¹

Reference

1. From Wikipedia: By Emw - Own work, CC BY-SA 3.0 https://commons.wikimedia.org/wiki/File:Protein_FCN2_PDB_2j0g.png