Combining chymotrypsin/trypsin digestion to identify hydrophobic proteins from oil bodies.

Oil bodies, lipid-storage organelles, are stabilized by a number of specific proteins. These proteins are very hydrophobic, which complicates their identification by "classical" proteomic protocols using trypsin digestion. Due to the lack of trypsin cleavage sites, the achievable protein coverage is limited or even insufficient for reliable protein identification. To identify such proteins and to enhance their coverage, we introduced a modified method comprising standard three-step procedure (SDS-PAGE, in-gel digestion, and LC-MS/MS analysis). In this method, chymotrypsin, single or in combination with trypsin, was used, which enabled to obtain proteolytic peptides from the hydrophobic regions and to identify new oil bodies' proteins. Our method can be easily applied to identification of other hydrophobic proteins.