LA-ICP-MS-quantitated boronate affinity magnetic Zr-MOFs prepared via post-modification for glycopeptides enrichment

Glycoproteins are critical in various biological processes and attract lots of attention of researchers. It still remains a challenge to detect glycopeptides by mass spectrometry because of their low abundance with heterogeneity and lability, as well as signal suppression by non-glycopeptides. The boronate affinity-based enrichment is an effective solution for detecting cis-diols-containing compounds including glycopeptides in complex matrices. However, there has not been any report about absolute quantitation of boron in the absorbent materials for glycopeptides, which obstructed the tailored design of boronate affinity materials and deeper understanding of interaction mechanisms.

This work presents the development of a boronic acid-functionalized magnetic zirconium metal-organic framework (mMOF-AAPBA) with actual boron content for specific capture of glycopeptides. The synthesized nanocomposite could enrich glycopeptides by magnetic solid-phase extraction (MSPE) via the synergistic effect of hydrophilic interaction and boronate affinity. After full characterization including quantitative analysis of boron by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), mMOF-AAPBA was applied as MSPE absorbent to capture glycopeptides. Under the optimized conditions, it could enrich 28 glycopeptides both from horseradish peroxidase and immunoglobulin digests, with a limit of detection of 1 fmol μL^-1 coupled with matrix-assisted laser desorption/ionization time of flight mass spectrometry. The boronate affinity absorbent also possessed great ability of anti-interference and good reusability. Furthermore, it possessed high performance in enriching glycopeptides in real samples including human saliva and traditional Chinese medicine injections.

In the preparation of the boron-containing nanocomposites, there is a special interest that an accurate protocol was established to assay boron based on LA-ICP-MS assisted by home-made matrix reference substances for the first time. These findings highlight the quantitative boron-containing mMOF-AAPBA as a robust affinity material for glycopeptide enrichment in real biological samples, offering potential applications in glycoproteomics and other cis-diols compound related researches.