Open AccessThe phosphorylation pattern of human α s1 ‐casein is markedly different from the ruminant species
Author(s) -
Sørensen Esben S.,
Møller Lise,
Vinther Maria,
Petersen Torben E.,
Rasmussen Lone K.
Publication year - 2003
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1046/j.1432-1033.2003.03755.x
Subject(s) - phosphorylation , casein kinase 2 , casein , casein kinase 1 , biochemistry , peptide sequence , amino acid , protein phosphorylation , biology , amino acid residue , chemistry , protein kinase a , gene , mitogen activated protein kinase kinase
Caseins are highly phosphorylated milk proteins assembled in large colloidal structures termed micelles. In the milk of ruminants, α s1 ‐casein has been shown to be extensively phosphorylated. In this report we have determined the phosphorylation pattern of human α s1 ‐casein by a combination of matrix‐assisted laser desorption mass spectrometry and amino acid sequence analysis. Three phosphorylation variants were identified. A nonphosphorylated form, a variant phosphorylated at Ser18 and a variant phosphorylated at Ser18 and Ser26. Both phosphorylation sites are located in the amino acid recognition sequence of the mammary gland casein kinase. Notably, no phosphorylations were observed in the conserved region covering residues Ser70–Glu78, which is extensively phosphorylated in the ruminant α s1 ‐caseins.