Primary structure of water buffalo α-lactalbumin variants A and B

Abstract

A novel electrophoretic α-lactalbumin (α-la) variant was detected in the Italian water buffalo breed. The isoelectric point of the variant, labelled A, was lower than the most frequent variant B. It presented an allelic frequency of 0·5% compared with the 97·1% of the BB allele. From Liquid Chromatography-Electrospray Ionization/Mass spectrometry, the molecular mass of the two α-la A and B variants were measured as 14235·1±0·8 and 14236·1±0·9 Da, respectively. The two proteins were sequenced and differentiated from one another by a single amino acid substitution, Asn⁴⁵(B)→Asp⁴⁵(A). As this amino acid substitution altered the N-glycosylation sequence consensus Asn45–X–Ser⁴⁶ it may be deduced that the protein glycosylation level of the α-la A would decrease.