Differences in Beef Quality between Angus (<i>Bos taurus taurus</i>) and Nellore (<i>Bos taurus indicus</i>) Cattle through a Proteomic and Phosphoproteomic Approach

Proteins are the major constituents of muscle and are key molecules regulating the metabolic changes during conversion of muscle to meat. Brazil is one of the largest exporters of beef and most Brazilian cattle are composed by zebu (Nellore) genotype. Bos indicus beef is generally leaner and tougher than Bos taurus such as Angus. The aim of this study was to compare the muscle proteomic and phosphoproteomic profile of Angus and Nellore. Seven animals of each breed previously subjected the same growth management were confined for 84 days. Proteins were extracted from Longissimus lumborum samples collected immediately after slaughter and separated by two-dimensional electrophoresis. Pro-Q Diamond stain was used in phosphoproteomics. Proteins identification was performed using matrix assisted laser desorption/ionization time-of-flight mass spectrometry. Tropomyosin alpha-1 chain, troponin-T, myosin light chain-1 fragment, cytoplasmic malate dehydrogenase, alpha-enolase and 78 kDa glucose-regulated protein were more abundant in Nellore, while myosin light chain 3, prohibitin, mitochondrial stress-70 protein and heat shock 70 kDa protein 6 were more abundant in Angus (P<0.05). Nellore had higher phosphorylation of myosin regulatory light chain-2, alpha actin-1, triosephosphate isomerase and 14-3-3 protein epsilon. However, Angus had greater phosphorylation of phosphoglucomutase-1 and troponin-T (P<0.05). Therefore, proteins involved in contraction and muscle organization, myofilaments expressed in fast or slow-twitch fibers and heat shock proteins localized in mitochondria or sarcoplasmic reticulum and involved in cell flux of calcium and apoptosis might be associated with differences in beef quality between Angus and Nellore. Furthermore, prohibitin appears to be a potential biomarker of intramuscular fat in cattle. Additionally, differences in phosphorylation of myofilaments and glycolytic enzymes could be involved with differences in muscle contraction force, susceptibility to calpain, apoptosis and postmortem glycolysis, which might also be related to differences in beef quality among Angus and Nellore.蛋白质是肌肉的核心组成成分，亦是调控肌肉向肉品转化过程中代谢变化的关键分子。巴西是全球最大的牛肉出口国之一，该国绝大多数肉牛均以瘤牛（Nellore，内洛尔牛）基因型为主。印度瘤牛（Bos indicus）牛肉通常较安格斯牛所属的普通牛（Bos taurus）更为精瘦且肉质更坚韧。本研究旨在对比安格斯牛与内洛尔瘤牛的肌肉蛋白质组与磷酸化蛋白质组特征。本研究选取两个品种各7头此前均接受统一生长管理的肉牛，实施为期84天的圈养饲养。于屠宰后即刻采集的腰最长肌（Longissimus lumborum）样本中提取蛋白质，并通过二维电泳进行分离。磷酸化蛋白质组学分析采用Pro-Q Diamond染料进行染色。蛋白质鉴定通过基质辅助激光解吸电离飞行时间质谱技术完成。原肌球蛋白α-1链、肌钙蛋白-T、肌球蛋白轻链-1片段、细胞质苹果酸脱氢酶、α-烯醇化酶与78 kDa葡萄糖调节蛋白在内洛尔牛中表达量显著更高；而肌球蛋白轻链3、增殖抑制蛋白（prohibitin）、线粒体应激蛋白70以及热休克蛋白70 kDa 6型在安格斯牛中表达量显著更高（P<0.05）。内洛尔牛的肌球蛋白调节轻链-2、α-肌动蛋白-1、磷酸丙糖异构酶与14-3-3蛋白ε的磷酸化水平更高；而安格斯牛的磷酸葡萄糖变位酶-1与肌钙蛋白-T的磷酸化水平则显著更高（P<0.05）。因此，参与肌肉收缩与肌纤维构建、在快肌或慢肌纤维中表达的肌丝蛋白，以及定位于线粒体或肌浆网、参与细胞钙流与细胞凋亡的热休克蛋白，可能与安格斯牛与内洛尔牛的牛肉品质差异相关。此外，增殖抑制蛋白（prohibitin）有望成为肉牛肌内脂肪含量的潜在生物标志物。另外，肌丝蛋白与糖酵解酶的磷酸化差异，可能与肌肉收缩力、钙蛋白酶敏感性、细胞凋亡以及死后糖酵解的差异相关，而这些差异同样可能与安格斯牛与内洛尔牛的牛肉品质差异有关。