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

Genetic screening of caseins in caprine milk samples enabled the identification of two novel ?-casein (?-CN) phenotypes, C2 and F1, expressed at lower levels (3.3 and 2.7 g L-1 per allele, respectively) than reference ?-CN C (4.7 g L-1 per allele), and another lacking in ?S-complex. The ?-CN C2 and F1 primary structures, determined by MS analysis, corresponded to ?-CN C and F, respectively. The reasonable hypothesis supporting the low expression of both variants considers the C2 and F1 alleles as deriving from ?-CN C1 and ?-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 ?-CN component was determined by a proteomic approach for the first time. Caprine milk containing low levels of antigenic ?S1-, ?S2- and ?-CN can be used for infant formula production and drinking milk for people with cows' milk protein allergy.