Zebrafish do not have a calprotectin ortholog

Area of Science:

• Immunology
• Biochemistry
• Comparative Genomics

Background:

• Calprotectin, a heterodimer of S100A8 and S100A9, is crucial for mammalian innate immunity, exhibiting antibacterial and pro-inflammatory roles.
• Understanding calprotectin's regulation and function aids in diagnostics and therapy for inflammatory diseases and host-microbe interactions.
• Previous studies suggested zebrafish s100a10b as a functional analog of calprotectin based on sequence and expression patterns.

Purpose of the Study:

• To investigate whether zebrafish possess a calprotectin ortholog or a paralog with convergent immune functions.
• To rigorously assess the antimicrobial and pro-inflammatory activities of candidate zebrafish S100 proteins.

Main Methods:

• Bioinformatic analysis to identify zebrafish S100 orthologs and paralogs.
• Recombinant expression and purification of four candidate zebrafish S100 proteins.
• In vitro assays for antimicrobial activity, transition metal binding site analysis via structural modeling, and Toll-like receptor 4 activation assays.

Main Results:

• Zebrafish lack orthologs for mammalian S100A8 and S100A9.
• None of the tested zebrafish S100 proteins, including s100a10b, demonstrated antimicrobial activity comparable to mammalian calprotectin.
• Structural modeling revealed no predicted antimicrobial transition metal binding sites in zebrafish S100 complexes, and none activated Toll-like receptor 4.

Conclusions:

• Zebrafish do not possess a calprotectin ortholog.
• No identified zebrafish S100 proteins have convergently evolved functions analogous to mammalian calprotectin's antimicrobial or pro-inflammatory roles.
• This study refutes the hypothesis of zebrafish s100a10b as a functional calprotectin equivalent.