Insertion of a casein kinase recognition sequence induces phosphorylation of ovine β-lactoglobulin in transgenic mice

Abstract

We have shown that the cellular mechanisms of the mammary gland can be used to produce a phosphorylated form of a normally unphosphorylated milk protein. This was achieved by the insertion of a β-casein DNA sequence coding for a group of mammary gland casein kinase recognition sites into ovine β-lactoglobulin. Transgenic mice carrying this modified gene were generated and lactating females were shown to produce a novel β-lactoglobulin in their milk. The infrared spectrum, reactivity to anti-phosphoserine antibody and reduction of electrophoretic mobility on treatment with alkaline phosphatase showed that the novel protein recovered from the milk whey (serum) was phosphorylated and molecular mass determination by mass spectrometry was consistent with the phosphorylation of one or two residues. A similar level of phosphorylation was measured by quantitative infrared spectroscopy. Centrifugation of the milk to pellet the casein micelles showed that most of the phosphorylated β-lactoglobulin was in the whey and hence not incorporated into casein micelles.