Hydrazide-functionalized magnetic microspheres for the selective enrichment of digested tryptophan-containing peptides in serum

The extreme complexity of protein samples is becoming a great challenge for proteomic analysis, especially for those having large dynamic range of protein abundance. To solve this problem, and to overcome the limitation of the current proteomic technologies, a new method using hydrazide-functionalized magnetic microspheres was established in this study. With this method, tryptophan (Trp)-containing peptides can be selectively and sensitively enriched from complex and low-volume samples. Furthermore, combined with 1D-LC-MS/MS analysis, the strategy was successfully applied to the proteomic study of mouse serum. The proportion of Trp-containing peptides was increased from 19.4% to 80.2% through enrichment, and the complexity of the sample was reduced more than two times. An additional 113 Trp-containing peptides and 48 novel proteins were detected compared to the conventional method. This enrichment method provides a means for identifying more proteins as potential biomarkers in serum and other complex samples.