Occurrence of quantitative genetic polymorphism at the caprine β-CN locus, as determined by a proteomic approach

Abstract

Genetic screening of caseins in caprine milk samples enabled the identification of two novel β-casein (β-CN) phenotypes, C2 and F1, expressed at lower levels (3.3 and 2.7 g L−1 per allele, respectively) than reference β-CN C (4.7 g L−1 per allele), and another lacking in αS-complex. The β-CN C2 and F1 primary structures, determined by MS analysis, corresponded to β-CN C and F, respectively. The reasonable hypothesis supporting the low expression of both variants considers the C2 and F1 alleles as deriving from β-CN C1 and β-CN A1 precursors, respectively, and characterised by a genic transition C→T negatively affecting the mRNA stability. Further, phosphorylation of Thr41 responsible for the 7P β-CN component was determined by a proteomic approach for the first time. Caprine milk containing low levels of antigenic αS1-, αS2- and β-CN can be used for infant formula production and drinking milk for people with cows' milk protein allergy.