Microscale solution IEF combined with 2-D DIGE substantially enhances analysis depth of complex proteomes such as mammalian cell and tissue extracts.

Current gel-based protein profiling methods such as 2-DE and fluorescent 2-D difference in gel electrophoresis (DIGE) evaluate small portions of complex proteomes. Hence, sample prefractionation is essential for more comprehensive proteome coverage and detection of low-abundant proteins. In this study, we describe the combination of DIGE labeling with microscale solution IEF (MicroSol-IEF) fractionation and subsequent analysis on slightly overlapping narrow pH range 2-D gels. By fluorescently tagging and mixing samples and controls prior to prefractionation, complications resulting from minor run-to-run variations during MicroSol-IEF separations of multiple samples are avoided. This greatly improves the reliability of quantitative comparisons. To illustrate its utility, this 3-D DIGE strategy was applied to analysis of human melanoma cells and mouse lung tissue extracts. Approximately 1000 reproducible spots can be obtained from narrow range 2-D gels of individual MicroSol-IEF fractions, and approximately 6000 spots can be obtained from entire proteomes. Quantitative changes in closely related samples could be more reliably detected and the method has a greatly increased capacity to distinguish between closely related protein isoforms. Thus the 3-D DIGE strategy produces a powerful method for more comprehensive and more reliable quantitative comparisons of protein profiles of very complex proteomes.