The primary structure of a low-Mr multiphosphorylated variant of beta-casein in equine milk.
Highly phosphorylated casein with a low molecular mass was isolated from Haflinger mare's milk by RP-HPLC. It accounts for 4.0% of the casein content. Its mass was determined by LC-ESI-MS before and after treatment by alkaline phosphatase. The molecular mass found for the apo-form (10,591 +/- 2 Da) is in agreement with its primary structure, which was established by ESI-MS/MS from tryptic peptides. It appeared that this short protein (94 amino acid residues) is an internally truncated form of the full-length equine beta-casein (226 residues). This low-Mr variant of equine beta-casein displays a large deletion (residues 50-181), due to a cryptic splice site usage occurring within exon 7 during the course of primary transcripts processing. The phosphorylation pattern of this equine beta-casein variant was investigated by LC-ESI-MS and 2-DE. Seven phosphorylation forms were identified with one to seven phosphate groups with pIs ranging between 4.67 and 4.01. The major isoforms carry five and six phosphate groups.
Miclo
Laurent
L
Unité de Recherche sur l'Animal et les Fonctionnalités des Produits Animaux , U.C. L'Institut National de la Recherche Agronomique 340, Nancy-Université, Vandoeuvre-lès-Nancy, France. Laurent.Miclo@scbiol.uhp-nancy.fr
Girardet
Jean-Michel
JM
Egito
Antonio S
AS
Mollé
Daniel
D
Martin
Patrice
P
Gaillard
Jean-Luc
JL
D000595:Amino Acid Sequence; D000818:Animals; D002364:Caseins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D015180:Electrophoresis, Gel, Two-Dimensional; D005260:Female; D006736:Horses; D013058:Mass Spectrometry; D008892:Milk / Q000737:chemistry*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010455:Peptides / Q000737:chemistry / Q000235:genetics; D020033:Protein Isoforms / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
D002364:Caseins; D010455:Peptides; D020033:Protein Isoforms