Deep Insight into the IntrinsicProteins of Sesame OBs by LC−MS/MS
In previous studies, the intrinsic proteins of sesame OBs were examined by SDS−PAGE (or Tricine−SDS−PAGE) combined with in-gel digestion and MALDI−MS or MALDI−MS/MS. It was clarified that on SDS−PAGE gel, there were two steroleosin bands with apparent MWs of 41 and 39 kDa, one caleosin band with apparent MW of 27 kDa, and two oleosin bands with apparent MWs of 17 and 15 kDa (Lin et al., 2005). These apparent MWs were well consistent with their corresponding theoretical MWs. On Tricine−SDS−PAGE gel, the apparent MWs of steroleosins, caleosin, and oleosins were smaller than the corresponding theoretical MWs, however (Zhao et al., 2016). By using in-gel digestion and MALDI−MS or MALDI−MS/MS, just one kind of protein was identified for each band (Lin et al., 2005; Zhao et al., 2016).
LC−MS/MS is a powerful tool used for proteomics with extremely high detection limit. In this study, the pH 7-OB was used for the LC−MS/MS analysis (Table 1). Comprehensively speaking, the results from LC−MS/MS were consistent with those from the two previous studies (Lin et al., 2005; Zhao et al., 2016). However, there were two kinds of steroleosins with MWs around 39 kDa. Here, please note that 11-beta-hydroxysteroid dehydrogenase-like 6 was similar protein to steroleosin (Katavic, Agrawal, Hajduch, Harris, & Thelen, 2006). In addition to 27 kDa caleosin, there were one kind of peroxygenase-like 6 (similar protein to caleosin) (Hanano et al., 2006) and four kinds of oil body-associated proteins with MWs around 27 kDa, but the five proteins showed obviously lower relative abundances than caleosin. Actually, three kinds of oleosins showed MWs around 17 kDa, while four kinds of oleosins had MWs around 15 kDa. It was found that the 17 (AAG23840.1) and 15 kDa (ACH85187.1) oleosins with high relative abundances were identified in previous studies (Zhao et al., 2016). To the best of our knowledge, this study was the first time to show the deep insight into the intrinsic proteins of sesame OBs.