Primary structure of ovine alpha s1-caseins: localization of phosphorylation sites and characterization of genetic variants A, C and D

J Dairy Res. 1995 May;62(2):281-96. doi: 10.1017/s0022029900030983.

Abstract

The primary structures of ovine alpha s1-casein variants A, C and D (formerly called Welsh variant) were determined. Separation of variants from whole casein was achieved using a fast and reliable reversed-phase HPLC method. Extended structural characterization of the purified proteins using electrospray mass spectrometry, automated Edman degradation and peptide mapping by means of HPLC-fast atom bombardment-mass spectrometry demonstrated that the mature protein was a mixture of two molecular species that differed in the deletion of residues 141-148 and were therefore 199 and 191 residues long respectively. The 199 residue peptide chain, which accounted for approximately 80% of the entire translated alpha s1-casein, was as long as its caprine and bovine counterparts, and had a 98 and 89% degree of identity with those two proteins respectively. Nine serine residues (positions 12, 44, 46, 64 to 68 and 75) were fully phosphorylated in alpha s1-casein A, whereas Ser115 and Ser41 were phosphorylated by approximately 50 and approximately 20% respectively. The differences between the three genetic variants A, C and D were simple silent substitutions, which however involved the degree to which the protein was phosphorylated. Variant C differed from variant A in the substitution Ser13-->Pro13 which determined the loss of the phosphate group on site 12 of the protein chain, SerP12-->Ser12. A further substitution, SerP68-->Asn68 caused the disappearance of both phosphate groups in the phosphorylated residues Ser64 and Ser66 in variant D; in this last casein variant there was no evidence of phosphorylation at Ser41.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Binding Sites
  • Caseins / chemistry*
  • Caseins / genetics
  • Caseins / metabolism
  • Cattle
  • Chromatography, High Pressure Liquid
  • Genetic Variation*
  • Molecular Sequence Data
  • Peptide Fragments / chemistry
  • Peptide Fragments / isolation & purification
  • Peptide Mapping
  • Phosphates / metabolism*
  • Phosphorylation
  • Phosphoserine / metabolism
  • Spectrometry, Mass, Fast Atom Bombardment
  • Trypsin / metabolism

Substances

  • Caseins
  • Peptide Fragments
  • Phosphates
  • Phosphoserine
  • Trypsin