Multivalent hydrazide-functionalized magnetic nanoparticles for glycopeptide enrichment and identification.

Among the common approaches for global glycopeptide enrichment, hydrazide chemistry is well recognized. However, conventional hydrazide-functionalized products are composed of a single layer of hydrazide functional groups. Due to the limited specific surface area of such a structure, the loading amount of hydrazide groups immobilized on these materials is restricted. Therefore, these materials can only provide a limited reaction rate with glycopeptides in complex protein samples, which is exacerbated by the microheterogeneities of glycosylation. Here, we introduce a new functionalized magnetic nanoparticle coating with hydrazide-modified non-crosslinked polymer chains. The multivalent hydrazide-functionalized particles were synthesized by the surface-initiated atom transfer radical polymerization (SI-ATRP) technique. The density of the hydrazide groups on the surface of these nanoparticles was three-fold higher than that of conventional single-layered materials. The new particles enabled the highly sensitive and selective enrichment of glycopeptides from a digestion mixture of fetuin, even from a background mixture of non-glycosylated protein that was 100-fold more abundant. The recovery ratio of glycopeptides was determined to be 77.8%, and the glycopeptide binding capacity of the materials was determined to be 25 μg mg(-1). Finally, the novel multivalent hydrazide-functionalized particles were applied in the enrichment of N-linked glycopeptides from mouse liver tissues, which resulted in the assignment of 511 unique glycopeptides belonging to 372 different glycoproteins. The results further demonstrated the potential of the multivalent particles for glycopeptide enrichment in complex proteomics samples.