Étude protéomique de la microhétérogénéité des caséines [alpha]s1 et [bêta] équines : identification des variants transcriptionnels et de phosphorylation ; identification des sites phosphorylés de la caséine [bêta]

Abstract : Equine [bêta]-casein ([bêta]-CN) and [alpha]s1-casein ([alpha]s1-CN) have a variable phosphorylation degree and are good models for the study of the influence of phosphorylation degree and peptide sequence on chelation of caseinophosphopeptides (CPP) with minerals of nutritional interest. Before considering such study, structure of caseins must be precisely determined. Our work has been devoted to the characterization of post-transcriptional and post-translational variants of [alpha]s1-CN and [bêta]-CN. Concerning [alpha]s1-CN, the full-length protein, three alternative splicing variants involving exons 7 and 14 and four variants involving cryptic splice site resulting in deletion of residue Gln91 have been identified in mare's milk after chromatographic fractionation and mass spectrometric analysis. The phosphorylation degree of these variants varies between 2 and 8 phosphate groups. Finally, 36 isoforms of [alpha]s1-CN have been identified. Isolation of each phosphorylation variant (having 3 to 7 phosphate groups) of [bêta]-CN by chromatography, and characterization of modified forms of [bêta]-CN by non enzymatic deamidation of residue Asn135 permits the establishment of bidimensional cartography of [bêta]-CN with precision. After hydrolysis by trypsin, CPP of each phosphorylation variant have been prepared by affinity chromatography to titanium dioxide, a recent technology, which allowed to locate by mass tandem spectrometry the phosphorylated sites of [bêta]-CN (Ser9, Ser10, Thr12, Ser18, Ser23, Ser24, Ser25). It was shown that the phosphorylation of [bêta]-CN is not a random process but follows a sequential way
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Aurélie Mateos. Étude protéomique de la microhétérogénéité des caséines [alpha]s1 et [bêta] équines : identification des variants transcriptionnels et de phosphorylation ; identification des sites phosphorylés de la caséine [bêta]. Sciences agricoles. Institut National Polytechnique de Lorraine, 2008. Français. ⟨NNT : 2008INPL089N⟩. ⟨tel-01753053⟩

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