title: MS-based characterization of α(s2)-casein isoforms in donkey's milk.
abstract: The primary structure of four α(s2)-casein (CN) isoforms, present as minor components in the dephosphorylated CN fraction of a milk sample collected in Eastern Sicily from an individual donkey belonging to the Ragusano breed at middle lactation stage, was determined, using the known donkey's α(s2)-CN (GenBank Acc. No. CAV00691; M(r) 26,028 Da) as reference. Proteins, with experimentally measured M(r) of 25,429, 21,939, 25,203 and 21,713 Da, were isolated by the combined use of reversed-phase high-performance liquid chromatography (RP-HPLC) and two-dimensional polyacrylamide gel electrophoresis. The major spot of each gel, corresponding to a single protein, was digested by trypsin, α-chymotrypsin and endoproteinase Glu-C. The resulting peptide mixtures were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and capillary RP-HPLC/nano-electrospray ionization tandem mass spectrometry, and the data obtained were used for the sequence determination. The isoforms are produced from differential splicing events involving exons 4, 5 and 6 and parts of the exon 17.
authors.affiliation: Department of Chemical Sciences, University of Catania, Viale A. Doria 6, I-95125, Catania, Italy.
authors.forename: Rosaria
authors.initials: R
authors.lastname: Saletti
authors.forename: Vera
authors.initials: V
authors.lastname: Muccilli
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Cunsolo
authors.forename: Debora
authors.initials: D
authors.lastname: Fontanini
authors.forename: Antonella
authors.initials: A
authors.lastname: Capocchi
authors.forename: Salvatore
authors.initials: S
authors.lastname: Foti
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002364:Caseins / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D015180:Electrophoresis, Gel, Two-Dimensional; D018397:Equidae; D008892:Milk / Q000737:chemistry*; D008969:Molecular Sequence Data; D020033:Protein Isoforms; D016415:Sequence Alignment; D020539:Sequence Analysis, Protein / Q000379:methods; D021241:Spectrometry, Mass, Electrospray Ionization; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D002364:Caseins; D020033:Protein Isoforms