Integrative profiling of metabolites and proteins: improving pattern recognition and biomarker selection for systems level approaches.

Methods such as mRNA expression profiling have provided a vast amount of genomic and transcriptomic information about plants and other organisms. However, there is explicit indication that considerable metabolic control is executed on the metabolite and on the protein level including protein modifications, thereby constituting the phenotypic plasticity. Consequently, the analysis of the molecular phenotype demands the step toward mass spectrometry (MS)-based postgenomic techniques such as metabolomics and proteomics. This chapter describes a straightforward protocol for simultaneously extracting metabolites and proteins from the same biological sample in preparation for MS analysis. Furthermore, protocols for profiling polar metabolites using gas chromatography time-of-flight MS and for shotgun proteomics using liquid chromatography-MS are discussed. A practical course is laid out that outlines all the basic steps, from harvesting to data analysis. These steps enable the correlative study of metabolite and protein dynamics with minimal technical variation. Biological variability of independent samples is exploited for variance analysis and pattern recognition.