Development and Characterization of a Fluorinated MS-Cleavable Cross-Linker for Structural Proteomics.

Cross-linking mass spectrometry (XL-MS) is an important method for studying three-dimensional protein structures and mapping protein-protein interactions. Some limitations of XL-MS still consist of its use for in-cell and in vivo applications. To date, cross-linking reagents are urgently needed that can efficiently penetrate the cell membrane to comprehensively map protein-protein interaction networks in intact cells. In this study, the fluorinated MS-cleavable cross-linker bis(pentafluorophenyl) ureido-4,4'-dibutyrate (DPFU) is described. DPFU is based on the MS-cleavable cross-linker disuccinimidyl dibutyric urea (DSBU) with the aim of balancing the hydrophobicity and solubility to improve membrane permeability. DPFU was evaluated for its solubility behavior in different detergent solutions to optimize conditions for its potential application in live cells. Using bovine serum albumin (BSA) as a model protein, XL-MS experiments were conducted across different temperatures and cross-linker concentrations. Solubility assays identified sodium dodecyl sulfate (SDS) as effective for enhancing DPFU solubility in an aqueous environment. DPFU yielded fewer cross-links for BSA than DSBU, highlighting limitations regarding its cross-linking efficiency under similar experimental conditions. This study provides the first insights into fluorinated cross-linkers, suggesting that further optimization is needed for a broader application of DPFU for future in-cell XL-MS studies.