Ti(IV) immobilized bisphosphate fructose-modified magnetic Zr metal organic framework (MOF) for specific enrichment of phosphopeptides

Abstract

Highly selective enrichment of low abundance phosphopeptides from intricate biological samples before mass spectrometry detection is a vital prerequisite for in-depth phosphoproteomics. Herein, a magnetic material mMOF-FBP-Ti4+ is fabricated by grafting UiO-66-NH2 metal–organic framework (Zr-MOF) onto the surface of Fe3O4, and subsequently immobilizing Ti(IV) on the mMOF with fructose 1,6-bisphosphate as chelating ligands. The obtained mMOF-FBP-Ti4+ showed large specific surface area (202.4 m2 g−1) and superparamagnetism (47.5 emu/g). The intrinsic Zr − O clusters of mMOF and the immobilized Ti(IV) ions on the surface of mMOF could interact with phosphopeptides as metal oxide affinity chromatography (MOAC) and immobilized metal affinity chromatography (IMAC), respectively. The introduction of fructose 1,6-bisphosphate also improved the hydrophilicity of the material, which enhanced the hydrophilic chromatography interaction (HILIC) between mMOF-FBP-Ti4+ and phosphopeptides. The above strong affinities provided low limit of detection (0.2 fmol μL−1), high selectivity (α-/β-casein/BSA tryptic digests with a mass ratio of 1:1:500), great reusability (three times circles) and good postenrichment recovery (90.2 %) towards phosphopeptides. Furthermore, the mMOF-FBP-Ti4+ was successfully applied to capture phosphopeptides from non-fat milk tryptic digest and human saliva, indicating its great potential for highly efficient enrichment of low-abundance phosphopeptides in complex biological samples.