The primary structure of water buffalo alpha(s1)- and beta-casein identification of phosphorylation sites and characterization of a novel beta-casein variant.
The primary structure of water buffalo alpha(s1)-casein and of beta-casein A and B variants has been determined using a combination of mass spectrometry and Edman degradation procedures. The phosphorylated residues were localized on the tryptic phosphopeptides after performing a beta-elimination/thiol derivatization. Water buffalo alpha(s1)-casein, resolved in three discrete bands by isoelectric focusing, was found to consist of a single protein containing eight, seven, or six phosphate groups. Compared to bovine alpha(s1)-casein C variant, the water buffalo alpha(s1)-casein presented ten amino acid substitutions, seven of which involved charged amino acid residues. With respect to bovine betaA2-casein variant, the two water buffalo beta-casein variants A and B presented four and five amino acid substitutions, respectively. In addition to the phosphoserines, a phosphothreonine residue was identified in variant A. From the phylogenetic point of view, both water buffalo beta-casein variants seem to be homologous to bovine betaA2-casein.
Ferranti
P
P
Dipartimento di Scienza degli Alimenti, Università degli Studi dI Napoli Federico II, Portici, Italy. ferranti@unina.it
Scaloni
A
A
Caira
S
S
Chianese
L
L
Malorni
A
A
Addeo
F
F
D000595:Amino Acid Sequence; D000818:Animals; D002020:Buffaloes; D002364:Caseins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D002417:Cattle; D007525:Isoelectric Focusing; D008894:Milk Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D008969:Molecular Sequence Data; D010766:Phosphorylation; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity