Dual-Functionalized Magnetic Bimetallic Metal-Organic Framework Composite for Highly Specific Enrichments of Phosphopeptides and Glycopeptides

Abstract In this work, a dual-functionalized magnetic bimetallic metal-organic framework composite denoted as Fe3O4@SiO2@(Zr-Ti-MOF)10-NH2 was ingeniously designed and fabricated by a facial layer-by-layer assembly technique. The composite not only exhibited strong affinity for phosphopeptide due to the coexistence of Zr-O clusters and Ti-O clusters, but also owned great hydrophilicity for glycopeptides relying on abundant hydrophilic NH2 groups, meeting the demand for simultaneously enrichment and sequential elution of phosphopeptides and glycopeptides. As expected, the synthesized composite showed great selectivity (1:2000 molar ratio of β-casein:BSA; 1:50 molar ratio of IgG:BSA), good sensitivity (1 fmol μL-1 for both α-casein and IgG), and good capacity (80 mg g-1 for α-casein and 200 mg g-1 for IgG). By using sequential elution strategy, 29 phosphopeptides and 24 glycopeptides from α-casein and IgG digests mixture could be simultaneously enriched and respectively detected through a single-step enrichment and sequential elution method. Furthermore, the composite was successfully applied to the analysis of intricate biological samples. 4 endogenous phosphopeptides and 20 phosphopeptides were trapped from human serum and non-fat milk tryptic digest respectively. From 0.5 mg of tryptic digest of rat brain, 141 N-linked glycopeptides corresponding to 127 glycoproteins and 918 phosphopeptides corresponding to 397 phosphoproteins were enriched simultaneously and identified respectively, proving the Fe3O4@SiO2@(Zr-Ti-MOF)10-NH2 to be a dependable candidate for the simultaneously enrichment of trace phosphopeptides and glycopeptides in intricate biological samples.