L-cysteine-modified metal-organic frameworks as multifunctional probes for efficient identification of N-linked glycopeptides and phosphopeptides in human crystalline lens

Highly selective enrichment of N-linked glycopeptides and phosphopeptides from complex biological samples is extremely important prior to mass spectrometry analysis due to their low abundance as well as numerous extrinsic interferences. In this work, L-cysteine (L-Cys)-modified multifunctional metalorganic frameworks denoted as Fe3O4@PDA@MIL-125@Au@ L-Cys (mMIL-125@Au@L-Cys) were prepared by modifications step by step. By combining hydrophilic interaction chromatography (HILIC) with metal oxide affinity chromatography (MOAC), the as-prepared material was firstly utilized to identify N-linked glycopeptides and phosphopeptides from tryptic digests of horseradish peroxidase (HRP) and beta-casein (beta-casein), respectively, with the help of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) and exhibited outstanding sensitivity (0.1 fmol mu L-1), great reusability (5 circles) and high selectivity (1: 100). Based on this, it was further applied into the enrichment of glycopeptides and phosphopeptides from tryptic digests of 100 mu g human crystalline lens proteins. In the end, 81 N-linked glycopeptides corresponding to 35 glycoproteins and 175 phosphopeptides ascribed to 55 phosphorylated proteins were identified, respectively. The remarkable results were benefitted from the merits of improved hydrophilicity from L-Cys, strong affinity of Ti-O centers, numerous reaction sites on the large surface of MOFs and superparamagnetism from Fe3O4 cores. The design of mMIL-125@Au@L-Cys not only served as a multifunctional probe for efficient identification of N-linked glycopeptides and phosphopeptides in human crystalline lens, but also set a precedent for fabricating more MOFs with post-modifications for further proteomics research. (C) 2019 Elsevier B.V. All rights reserved.