Proteomic characterisation and phylogenetic derivation of ovine ?S1-CN B and ?S1-CN G genetic variants

A combination of chromatographic, immunoelectrophoretic and mass spectrometric methods was applied to healthy individual milk of ovine massese breed. Caseome of ?S1-casein (?S1-CN) fraction was characterised in homozygous and heterozygous phenotypes for the novel B and G genetic variants. Using ovine ?S1-CN C counterpart as reference, amino acid substitutions and phosphorylated components were determined. The replacement of p.Arg90>His and p.Ile194>Thr were found in ?S1-CN B variant, while the single p.Ile194>Thr substitution occurred in ?S1-CN G variant. The quali-quantitative composition of phosphorylated ?S1-CN components in milk of animals bearing each variant was defined, highlighting possible genetic markers for assessment of dairy product quality. The heterogeneity of the electrophoretic profiles of the corresponding caseomes was due to the number of phosphorylated components and their net charge and pI values, and updated the ovine ?S1-CN phylogenetic tree, suggesting ?S1-CN G as the ancestral variant of ?S1-CN B and other variants.