DM9 Domain Containing Protein Functions As a Pattern Recognition Receptor with Broad Microbial Recognition Spectrum

Area of Science:

• Immunology
• Molecular Biology
• Marine Biology

Background:

• The DM9 domain is found in proteins across diverse species, suggesting conserved functions.
• DM9 domain-containing proteins (DM9CPs) integrate with various protein domains, indicating complex biological roles.
• Understanding DM9CPs is crucial for invertebrate immunity and evolutionary biology.

Purpose of the Study:

• To investigate the biological function and molecular determinants of the DM9 domain using CgDM9CP-1 from the oyster *Crassostrea gigas*.
• To characterize the ligand-binding specificity and pattern recognition capabilities of CgDM9CP-1.
• To elucidate the structural basis of CgDM9CP-1's molecular recognition activity.

Main Methods:

• Protein modeling and characterization of CgDM9CP-1 from *Crassostrea gigas*.
• Ligand-binding assays to determine specificity for d-mannose and pathogen-associated molecular patterns (PAMPs).
• Crystal structure analysis of wild-type and mutant CgDM9CP-1 to identify critical residues for ligand recognition.
• Subcellular localization studies in *C. gigas* hemocytes.

Main Results:

• CgDM9CP-1 exhibits high binding specificity and avidity for d-mannose residues.
• CgDM9CP-1 functions as a pattern recognition receptor (PRR) recognizing diverse PAMPs (LPS, peptidoglycan, mannan, β-1,3-glucan) in a d-mannose-dependent manner.
• Structural analysis identified Asp22 and Lys43 as critical residues for ligand recognition.
• CgDM9CP-1 localizes to the hemocyte surface and translocates to the cytoplasm upon microbial engulfment.

Conclusions:

• CgDM9CP-1 is a functional PRR in *Crassostrea gigas*, playing a role in innate immunity.
• The DM9 domain's d-mannose binding capability is essential for its pattern recognition function.
• This study provides insights into the molecular mechanisms of DM9CPs in invertebrate immune responses.