TWO-DIMENSIONAL ELECTROPHORESIS IN COMBINATION WITH MASS SPECTROMETRY TO STUDY NELLORE CATTLE DIVERGENTLY GROUPED FOR MEAT QUALITY OR FEED EFFICIENCY TRAITS

Brazilian beef production is the second largest in the world, and 80% of the national herd has the influence of Bos indicus cattle, mainly Nellore breed. However, few studies have used a proteomic approach to investigate some important traits such as meat quality or feed efficiency (FE) of this breed. We described results two proteomic studies with Nellore cattle based on the separation of proteins (muscle or liver) by two-dimensional gel electrophoresis (2D-PAGE) and protein characterization by electrospray ionization mass spectrometry (ESI-MS). In study I, meat samples (L. thoracis) of 1084 animals were used and the meat tenderness was measured as shear force (SF). A total of 40 specimens were selected and divided into two groups: animals with tender meat (TE) or tough meat (TO), in which SF was 4.07 ± 0.68 and 7.58 ± 1.53 kg, respectively. In study II, Nellore cattle were classified according to FE as residual feed intake (RFI). After weaning, 128 Nellore cattle underwent a FE test to identify their RFI class (low or high). this total, 20 animals were assigned to the finishing period in individual pens. Low RFI animals (more efficient, n = 10) consumed -1.16 kg / day, whereas high RFI animals (less efficient, n = 10) consumed +1.22 kg / day. The animals were slaughtered with an average body weight of 557.65 ± 10.39 kg. In studies I and II, approximately 3 g of muscle and hepatic tissue each group were used for protein extraction. A 250 µg protein mass was used for the first dimension of 2D-PAGE. Bovine muscle or liver extracts were loaded onto 13 cm isoelectric focusing strips with a pH 3-10 and 4-7 gradient immobilized on ampholytes. The gels of the groups in both approaches (TO vs. TE; or High vs. Low-RFI) were scanned and the images were analyzed using the ImageMaster Platinum software to measure isoelectric point and molecular weight proteins parameters. The protein spots in which volume (V%) and relative intensity differed (P < 0.05) among experimental groups were selected for characterization by ESI-MS methods. The tryptic digestion was performed using a DigestZP In-Gel kit and the ESI-MS runs were processed using ProteinLynx Global Server (Waters) software and analyzed in the database using the MASCOT system (Matrix Science). In muscle, the mean number of protein spot found in the TE and the TO group gels were 186 ± 20 and 146.5 ± 16.5, respectively. In liver (study II), protein spot High and Low-RFI groups were 279 ± 30 and 215 ± 26, respectively. The 2D-PAGE and ESI-MS efficiently separated and allowed the identification of proteins in muscle and liver. Pyruvate kinase (PK) was inferred to be related to beef tenderness (TO vs. TE), whereas hemoglobin (HB) was related to FE (High vs. Low RFI) in liver. The biological functions of these proteins, such as glycolytic metabolism (PK) or oxygen transport activity (HB), may help to explain phenotypic differences in Nellore cattle.