The Primary Structure of Caprine PP3: Amino Acid Sequence, Phosphorylation, and Glycosylation of Component PP3 from the Proteose-Peptone Fraction of Caprine Milk

¹ Protein Chemistry Laboratory, Department of Molecular and Structural Biology, University of Aarhus, DK-8000 Aarhus, Denmark

Proteose-peptone component 3 is a phosphorylated glycoprotein that was isolated from the proteosepeptone fraction of caprine milk. By mass spectrometric analysis, amino acid sequencing, and polymerase chain reaction analysis, the primary structure has been determined and has been shown to contain 136 amino acids. Phosphorylations were identified at Ser₃₀ and Ser₄₁. A partial glycosylation was present at Thr₁₆, and a N-linked glycosylation was present at Asn₇₈. Galactosamine was the amino sugar detected at Thr₁₆. Glucosamine and galactosamine were the amino sugars found in the carbohydrate group linked to Asn₇₈. The caprine amino acid sequence exhibits 88% identity with the bovine proteose-peptone component 3 sequence. However, when compared with the bovine sequence, the caprine sequence contains an insertion of a serine residue at position 25.

Key Words: proteose-peptone component 3 • caprine milk • primary structure • amino acid sequence

Submitted on November 26, 1997
Accepted on March 27, 1998