Detection and sequence determination of a new variant beta-lactoglobulin II from donkey.
The sequence determination of a new variant of beta-LG II, detected as a minor component by reversed-phase high-performance liquid chromatography/electrospray ionization mass spectrometry (RP-HPLC/ESI-MS) analysis of the whey fraction from a milk sample taken from an individual donkey belonging to the 'Ragusana' species of eastern Sicily, is reported. Direct RP-HPLC/ESI-MS analysis of the whey fraction from this milk sample allowed the identification of a new variant of beta-LG II, based on the determination of the M(r) of the intact protein. The new protein, with an experimentally determined M(r) of 18311 Da, was detected as a minor component in the whey fraction investigated. Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF)MS and RP-HPLC/ESI-MS/MS analyses of the tryptic digest of the new protein demonstrate that it presents two amino acid substitutions with respect to the sequence of beta-LG II A, namely a substitution Pro-->Cys at position 110, and a substitution Asp-->Gly at position 162. The disulfide bonds between the four cysteines, not directly determined in donkey's and horse's beta-LG II, were shown to occur between Cys(106)-Cys(120) and Cys(66)-Cys(161), as in other mammalian beta-LGs. The new beta-LG II variant from donkey was named D.
Cunsolo
Vincenzo
V
Dipartimento di Scienze Chimiche, Università degli Studi di Catania, Viale A. Doria 6, I-95125 Catania, Italy.
Costa
Alessia
A
Saletti
Rosaria
R
Muccilli
Vera
V
Foti
Salvatore
S
D000595:Amino Acid Sequence; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D018397:Equidae; D007782:Lactoglobulins / Q000032:analysis / Q000737:chemistry*; D008892:Milk / Q000737:chemistry*; D008894:Milk Proteins / Q000737:chemistry; D008969:Molecular Sequence Data; D020539:Sequence Analysis, Protein; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D053719:Tandem Mass Spectrometry; D014357:Trypsin / Q000737:chemistry; D000067816:Whey Proteins
D007782:Lactoglobulins; D008894:Milk Proteins; D000067816:Whey Proteins; D014357:Trypsin