Cunsolo Vincenzo, Costa Alessia, Saletti Rosaria, Muccilli Vera, Foti Salvatore
Dipartimento di Scienze Chimiche, Università degli Studi di Catania, Viale A. Doria 6, I-95125 Catania, Italy.
Rapid Commun Mass Spectrom. 2007;21(8):1438-46. doi: 10.1002/rcm.2978.
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.
报道了从西西里岛东部“拉古萨纳”品种的一头驴的乳样乳清组分中，通过反相高效液相色谱/电喷雾电离质谱（RP-HPLC/ESI-MS）分析检测到的一种次要成分——β-乳球蛋白II新变体的序列测定。对该乳样乳清组分进行直接RP-HPLC/ESI-MS分析，基于完整蛋白质的相对分子质量（M(r)）测定，鉴定出一种β-乳球蛋白II新变体。在研究的乳清组分中检测到一种新蛋白质，其实验测定的M(r)为18311 Da，是次要成分。对该新蛋白质胰蛋白酶消化产物进行基质辅助激光解吸/电离飞行时间（MALDI-TOF）质谱和RP-HPLC/ESI-MS/MS分析表明，相对于β-乳球蛋白II A序列，它有两个氨基酸取代，即在第110位Pro→Cys取代，在第162位Asp→Gly取代。与其他哺乳动物β-乳球蛋白一样，驴和马的β-乳球蛋白II中未直接测定的四个半胱氨酸之间的二硫键显示存在于Cys(106)-Cys(120)和Cys(66)-Cys(161)之间。来自驴的新β-乳球蛋白II变体命名为D。
