Secretory proteins as potential semiochemical carriers in the horse.

The research identifies two soluble proteins in horse sweat and parotid gland as potential carriers for semiochemicals, substances involved in chemical communication between animals. One protein, lipocalin allergen EquC1, shows selectivity for volatile compounds with a specific chain structure, suggesting a role in the chemical communication between horses. The second protein belongs to the parotid secretory proteins group, but its specific function remains unclear.

Introduction and Objective

• This study centered on the investigation of secretory proteins in horse sweat and parotid gland. The aim was to establish if these proteins play a role in semiochemical transport, which involves substances that trigger communication between animals via chemical signals.

Protein Characterization

• Two soluble proteins were identified and characterized for structural and functional properties. The first, lipocalin allergen EquC1, is already known though the study refined its understanding. The second protein is newly reported in horses and belongs to a group of parotid secretory proteins.

Lipocalin Allergen EquC1

• This protein was reviewed for its glycosylation sites, areas where sugar chains attach to proteins. The protein had a different glycosylation pattern than previously reported.
• The protein, when purified from horse sweat, contained oleamide and other organic molecules. The researchers suggest this protein could be acting as a carrier for these molecules.
• Binding experiments conducted indicated selectivity toward volatile compounds with 9-11 carbon chains, suggesting this protein could be involved in the chemical communication between horses.

Parotid Secretory Protein

• The second protein was sequenced and its post-translational modifications studied. This protein has cysteine residues, two of which were involved in a disulfide bridge, a bond that helps stabilize a protein’s structure.
• A model based on similar proteins showed this protein has a long hydrophobic barrel, a structural feature common in proteins involved in binding and transport activities.
• However, binding experiments failed to identify any specific ligands for this protein, leaving its physiological role undefined in this study.

Conclusion

• The research provides compelling evidence that the lipocalin allergen EquC1 protein could be involved in semiochemical communication in horses. The role of the parotid secretory protein, however, remains unclear.