title: Casein-derived bioactive phosphopeptides: role of phosphorylation and primary structure in promoting calcium uptake by HT-29 tumor cells.
abstract: Casein phosphopeptides beta-CN(1-25)4P and alpha(s1)-CN(59-79)5P, from beta- and alpha(s1)-casein, respectively, both carrying the characteristic 'acidic motif' Ser(P)-Ser(P)-Ser(P)-Glu-Glu, were chemically synthesized and administered to HT-29 cells differentiated in culture, which are a used model of intestinal epithelium for absorption studies. Both casein phosphopeptides caused an increase of [Ca(2+)](i) due to influx of extracellular Ca(2+). The response was quantitatively higher with beta-CN(1-25)4P than alpha(s1)-CN(59-79)5P. The synthetic peptide corresponding to the 'acidic motif' was ineffective and the dephosphorylated form of beta-CN(1-25)4P almost inactive. The lack of the N-terminally located five amino acids, or sequence modifications within the N-terminal segment of beta-CN(1-25)4P, caused a total loss of activity, whereas the lack of the C-terminal segment preserved activity. In conclusion, the influx of calcium into HT-29 cells caused by beta-CN(1-25)4P appears to depend on the phosphorylated 'acidic motif' and the preceding N-terminal region.
authors.affiliation: The Medical Faculty, University of Milan, L.I.T.A., Via Fratelli Cervi 93, 20090 Segrate, Milan, Italy.
authors.forename: Anita
authors.initials: A
authors.lastname: Ferraretto
authors.forename: Claudia
authors.initials: C
authors.lastname: Gravaghi
authors.forename: Amelia
authors.initials: A
authors.lastname: Fiorilli
authors.forename: Guido
authors.initials: G
authors.lastname: Tettamanti
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism*; D002364:Caseins / Q000737:chemistry* / Q000494:pharmacology*; D019073:HT29 Cells; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D017136:Ion Transport; D007700:Kinetics; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry* / Q000494:pharmacology*; D010748:Phosphopeptides / Q000737:chemistry / Q000494:pharmacology; D010766:Phosphorylation
chemical_list: D002364:Caseins; D010446:Peptide Fragments; D010748:Phosphopeptides; C092814:alpha-casein (59-79); C412562:caseinophosphopeptide 1-25; D002118:Calcium