Hagfish C1q: its unique binding property.

Area of Science:

• Immunology
• Marine Biology
• Biochemistry

Background:

• The complement system is crucial for innate immunity, involving pattern-recognition molecules (PRMs) that identify and eliminate pathogens.
• Hagfish possess a unique immune system, and understanding their PRMs offers insights into early vertebrate immune evolution.
• C1q is a key PRM in mammalian complement, initiating classical pathway activation.

Purpose of the Study:

• To identify and characterize a novel pattern-recognition molecule in the hagfish complement system.
• To determine the molecular identity and microbial binding properties of this hagfish PRM.
• To elucidate the specific molecular targets recognized by the hagfish PRM on microbial surfaces.

Main Methods:

• Hagfish serum proteins were purified using GlcNAc-agarose affinity chromatography and sequential elution with GlcNAc and EDTA.
• Protein identification was performed using SDS-PAGE, and a C1q homolog was identified via cDNA analysis.
• Microbial binding assays were conducted in a Ca(2+)-dependent manner, with target specificity determined using various microbial components and affinity matrices.

Main Results:

• A 26 kDa protein, identified as hagfish C1q (HaC1q), was isolated from the EDTA eluate.
• HaC1q demonstrated Ca(2+)-dependent binding to microbial ligands including lipopolysaccharide, lipoteichoic acid, and peptidoglycan.
• HaC1q specifically bound to GlcNAc-agarose and Sepharose 6B, indicating agarobiose as a target, with high density required for stable binding.

Conclusions:

• Hagfish C1q (HaC1q) functions as a pattern-recognition molecule in the hagfish innate immune system.
• HaC1q recognizes agarobiose-like structures on microbial surfaces, mediating pathogen elimination.
• The findings provide insights into the evolution of C1q and complement-mediated immunity in primitive vertebrates.