Identification of major milk fat globule membrane proteins from pony mare milk highlights the molecular diversity of lactadherin across species.

The research article investigates the milk fat globule (MFGM) proteins found in mare’s milk, a topic previously unexplored, and compares these proteins to those in cow and goat milk. The researchers identified certain common MFGM proteins across the species but also found notable differences in butyrophilin and lactadherin in mare’s milk.

Study Objective and Methodology

• The study aimed to catalog and describe the MFGM proteins present in mare milk in order to understand the specific protein structure in Equidae milk and compare it with Bovidae (cow and goat) milk.
• In this study, mass spectrometry was used to identify major MFGM proteins in mare milk. Notably, the researchers wanted to compare xanthine oxidase, butyrophilin, lactadherin, and adipophilin from mare milk to their counterparts in cow and goat milk.
• Polymerase chain reaction experiments were conducted on the lactadherin transcripts isolated from the milk fat globules.
• Liquid chromatography coupled with tandem mass spectrometry analyses was also performed to confirm the existence of both lactadherin variants in mare MFGM.

Findings from the Study

• While major MFGM proteins that were already identified in cow or goat milk were also found in mare milk, there were observed differences in the MFGM proteins butyrophilin and lactadherin in mare milk.
• The equine butyrophilin was found to be a highly glycosylated 70-kDa protein, different from the 64 and 67 kDa proteins identified in cow and goat butyrophilin.
• More significant differences were observed in lactadherin. In contrast to the one or two polypeptide chains identified in caprine and bovine lactadherin, four isoforms of lactadherin of varying sizes were identified in mare milk
• Two distinct lactadherin transcripts were also identified in the horse mammary gland. Their sequences revealed a potential alternative use of a splice site in the equine lactadherin-encoding gene. This event results in an extra alanine residue in the lactadherin protein sequence, which disrupts a potential atypical N-glycosylation site.

Conclusions Drawn from the Study

• Findings from this study indicate that lactadherin from Equidae milk is more complex than that found in cow and goat milk from the Bovidae family.
• This complexity raises questions about the specific function of these different isoforms in the equine mammary gland, suggesting that further research is necessary to understand this phenomenon.