The primary structure of the ovine beta-caseins

Area of Science:

• Biochemistry
• Proteomics
• Dairy Science

Background:

• Ovine whole casein comprises multiphosphorylated beta-casein components.
• Two distinct components, beta 1 and beta 2-caseins, have been identified.

Purpose of the Study:

• To determine the complete amino acid sequence of ovine beta 1-casein.
• To elucidate the structural differences between ovine beta 1 and beta 2-caseins.
• To compare ovine beta-casein structure with its bovine counterpart.

Main Methods:

• Cyanogen bromide and tryptic digestion were employed.
• Amino acid sequencing was performed on the resulting peptides.
• Hydrophobicity and phosphorylation sites were analyzed.

Main Results:

• Ovine beta 1 and beta 2-caseins share the same polypeptide chain, differing in phosphate content (6 and 5, respectively).
• Ovine beta 1-casein exhibits deletions and conservative amino acid substitutions compared to bovine beta-casein A2.
• Key structural features, including phosphorylated serine clusters and charged amino-terminal regions, are conserved.

Conclusions:

• The substitution of isoleucine at position 12 in bovine beta-casein to threonine in ovine beta-casein creates a new phosphorylation site.
• Partial phosphorylation at this site explains the existence of both ovine beta 1 and beta 2-caseins.
• Ovine beta-casein displays significant homology to bovine beta-casein A2, with distinct phosphorylation patterns.