Characterization of an Equine α-S2-Casein Variant Due to a 1.3 kb Deletion Spanning Two Coding Exons.

The study examines mare’s milk, focusing on characterizing two main forms of a milk protein called equine αS2-casein. The researchers uncovered that these two forms resulted from a 1.3 kilobase deletion within the genome that spans two coding exons.

Background of the Study

• The investigation was performed as mare’s milk has become increasingly significant in Europe due to its health benefits and lower allergenic potential compared to cows’ milk.
• The allergenicity of milk can be affected by different genetic variants, so the researchers set out to explore these in relation to mare’s milk, which has been less studied in this way than classical dairy species’ milk.

Discovery of Genetic Variability

• The researchers discovered two main types of a particular protein called equine αS2-casein in mare’s milk, which they found to be the result of a genomic 1.3 kilobase in-frame deletion encompassing two coding exons.
• One of these exons represents a genetic duplication specific to equids, which is a group of mammals that includes horses and related animals.
• Validation of these discoveries was performed through cDNA sequencing from mare’s milk of horses with different genotypes.

Verification at Protein Level

• The research team also confirmed at the protein level using SDS-page and in-gel digestion techniques with subsequent LC-MS analysis that both proteins resulting from the genomic deletion were actually being expressed in the mare’s milk.

Historical Development of the Deletion

• The team also compared the sequence with already published sequences from other members of the Equidae family and confirmed that the deletion likely happened before the ancestor of present-day asses and zebras diverged from the horse lineage.

In conclusion, the study adds new insights to the understanding of the genetic variability in mare’s milk and the allergenicity of horse milk proteins.