Mass spectral analysis of domestic and wild equine apoA-I and A-II: detection of unique dimeric forms of apoA-II.

The research explores the protein structure of apolipoprotein A-II in different species of horses and donkeys. The study identified unique dimeric forms of the protein and suggests that small amounts of it and apoA-I are acylated.

Objective of the Research

• The purpose of the study was to determine whether the apoA-II of different species of horses and donkeys form monomers or dimers, that is, whether they remain as single units or pair up. The researchers were particularly interested in identifying differences in protein structure among different equine species.

Methods Used

• The research team isolated high density lipoproteins from the plasma of seven different equines: a domestic horse, a donkey, two types of zebras, a Przewalski’s horse, a Somali ass, and a kiang.
• The researchers used a combination of ultracentrifugation and liquid chromatography with electrospray-ionization mass spectrometry to determine the molecular masses of apoA-I and apoA-II.

Observations and Conclusions

• The study found that apolipoprotein A-II forms homodimers (i.e., two identical proteins) in all seven equines. This suggests that, unlike the apolipoprotein A-II of other primates, the equine version of this protein consistently forms pairs.
• The researchers discovered unique dimers in donkeys. The dimers consisted of proapolipoprotein A-II linked to either a mature apoA-II monomer or another proapoA-II via a disulfide bond.
• The study’s data also indicate that small amounts of apoA-I and apoA-II are acylated. Acylation is a process in which an acyl group is added to a compound, suggesting that these proteins might undergo a modification after they’re produced.