Ser71 of αS1‐Casein is Phosphorylated in Breast Milk—Evidence from Targeted Mass Analysis. Issue 12 (4th October 2017)

• Record Type: Journal Article
• Authors: König, Simone; Altendorfer, Irina; Saenger, Thorsten; Bleck, Ellen; Vordenbäumen, Stefan; Schneider, Matthias; Jose, Joachim
• Is Part Of: Molecular nutrition & food research. Volume 61:Issue 12(2017)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2017-10-04
• Subjects: αS1‐casein -- breast milk -- mass spectrometry -- phosphorylation -- phosphosite S71; Food -- Biotechnology -- Periodicals; Food -- Microbiology -- Periodicals; Nutrition -- Periodicals; Food -- Toxicology -- Periodicals; Nutrition -- Periodicals; Food Microbiology -- Periodicals; Food Technology -- Periodicals; Molecular Biology -- Periodicals; 664.0705
• DOI: 10.1002/mnfr.201700496
• Languages: English
• ISSNs: 1613-4125

Abstract

Abstract : Scope: The casein phosphoproteins in mother's milk supply calcium and phosphate ions and make them biologically available to the newborn. Human αS1‐casein is of particular interest being also an autoantigen and proinflammatory cytokine. Phosphorylation of αS1‐casein by casein kinase 2 completely abolishes binding to toll‐like receptor 4 and proinflammatory effects. It is, however, not known, which amino acids are affected. Therefore, breast milk samples were analyzed in an effort to detect the phosphorylation sites of αS1‐casein. Methods and results: Breast milk samples were tryptically digested. Target tandem MS analysis confirmed the known phosphorylation sites S33 and S41; evidence for pS89 was found in some samples. Experimental support for the presence of pS31 and pS34 was weak. Phosphorylation of a new site in αS1‐casein, S71, was reproducibly measured in all samples, albeit at much lower intensity than pS33 and pS41. Conclusion: Phospho‐occupancy rates varied greatly and could not be confidently correlated to other parameters within the cohort of 20 donors. The new phosphosite S71 is located in the neighborhood of the serine‐rich region and may contribute to the cluster of high charge density at normal milk pH, likely exerting an influence on protein tertiary structure and thus function. Abstract : αS1‐casein phosphorylation at S71 is detected in breast milk by tandem mass spectrometry. The site is located in a sequences region different from that in other mammalian species but close to the conserved phosphoserine‐rich region. Phosphorylation at S71 influences the local negative charge density with an impact on protein tertiary structure.