Facile preparation of titanium functionalized cross-linked chitosan polymer for phosphoproteome analysis in serum.

Efficient phosphopeptide enrichment is extremely important for proteomics research. In this work, chitosan (CTs), 2,3-dihydroxyterephthalaldehyde (2,3-DHA), and carbohydrazide (CHZ) are polymerized to generate the polymer (DHA-CTs-CHZ), and then the polymer (DHA-CTs-CHZ) is coupled with a significant number of titanium ions to enrich phosphopeptides. The material exhibits high selectivity (5000:1 M ratio of BSA to β-casein), sensitivity (0.001 fmol/μL), loading (83.3 μg/mg), recovery (98.6 ± 1.2 %), and effective size exclusion for phosphopeptide enrichment. In addition, 46 phosphopeptides and 31 phosphorylated sites associated with 27 phosphorylated proteins were successfully captured from the serum of normal subjects, while 47 phosphopeptides and 35 phosphorylated sites associated with 30 phosphorylated proteins were successfully captured from Alzheimer's disease (AD) patients' serum.