Phosphorylation of α_(s1)-casein is regulated by different genes

摘要

Casein phosphorylation is a posttranslational modification catalyzed by kinase enzymes that attach phosphate groups to specific A A in the protein sequence. This modification is one of the key factors responsible for the stabilization of calcium phosphate nanoclusters in casein micelles and for the internal structure of the casein micelles. α_(s1)-Casein (α_(s1)-CN) is of special interest because it constitutes up to 40% of the total casein fraction in milk, and it has 2 common phosphorylation states, with 8 (α_(s1)-CN-8P) and 9 (α_(s1)-CN-9P) phosphor-ylated serine residues. Factors affecting this variation in the degree of phosphorylation are not currently known. The objective of this research was to determine the genetic background of α_(s1)-CN-8P and α_(s1)-CN-9P. The genetic and phenotypic correlation between α_(s1)-CN-8P and α_(s1)-CN-9P was low (0.18 and 0.19, respectively). This low genetic correlation suggests a different genetic background. These differences were further investigated by means of a genome-wide association study, which showed that both α_(s1)-CN-8P and α_(s1)-CN-9P were affected by a region on Bos taurus autosome (BTA) 6, but only α_(s1)-CN-8P was affected by a region on BTA11 that contains the gene that encodes for β-lactoglobulin (β-LG), and only α_(s1)-CN-9P was affected by a region on BTA14 that contains the diacylglycerol acyltransfer-ase 1 (DGAT1) gene. Estimated effects of (3-LG protein genotypes showed that only α_(s1)-CN-8P was associated with the β-LG A/B polymorphism (g.1772G＞A and g.3054C＞T); the AA genotype of (3-LG was associated with a lower concentration of α_(s1)-CN-8P (-0.32% wt/ wt) than the BB genotype (+0.41% wt/wt). Estimated effects of DGAT1 K232A genotypes showed that only α_(s1)l-CN-9P was associated with the DGAT1 gene polymorphism; DGAT1 AA genotype was associated with a higher α_(s1)-CN-9P concentration (+0.53% wt/wt) than the DGAT1 KK genotype (-0.44% wt/wt). The results give insight in phosphorylation of α_(s1)l-CN-8P and α_(s1)- CN-9P, which seem to be regulated by a different set of genes.