A Rapid and Reliable Method for Total Protein Extraction from Succulent Plants for Proteomic Analysis

Crassulacean acid metabolism plants have some morphological features, such as succulent and reduced leaves, thick cuticles, and sunken stomata that help them prevent excessive water loss and irradiation. As molecular constituents of these morphological adaptations to xeric environments, succulent plants produce a set of specific compounds such as complex polysaccharides, pigments, waxes, and terpenoids, to name a few, in addition to uncharacterized proteases. Since all these compounds interfere with the analysis of proteins by electrophoretic techniques, preparation of high quality samples from these sources represents a real challenge. The absence of adequate protocols for protein extraction has restrained the study of this class of plants at the molecular level. Here, we present a rapid and reliable protocol that could be accomplished in 1 h and applied to a broad range of plants with reproducible results. We were able to obtain well-resolved SDS/PAGE protein patterns in extracts from different members of the subfamilies Agavoideae (Agave, Yucca, Manfreda, and Furcraea), Nolinoideae (Dasylirion and Beucarnea), and the Cactaceae family. This method is based on the differential solubility of contaminants and proteins in the presence of acetone and pH-altered solutions. We speculate about the role of saponins and high molecular weight carbohydrates to produce electrophoretic-compatible samples. A modification of the basic protocol allowed the analysis of samples by bidimensional electrophoresis (2DE) for proteomic analysis. Furostanol glycoside 26-O-β-glucosidase (an enzyme involved in steroid saponin synthesis) was successfully identified by mass spectrometry analysis and de novo sequencing of a 2DE spot from an Agave attenuata sample.