Divide and conquer: cleavable cross-linkers to study protein conformation and protein–protein interactions

Chemical cross-linking combined with mass spectrometry (MS) and computational modeling has evolved as an alternative method to address fundamental questions in structural biology. The constraints revealed by the cross-links yield valuable distance information and allow one to deduce three-dimensional structural information on very large and transient protein complexes. During the past few years, technical advances in the cross-linking/MS approach have been enormous, mainly owing to the fantastic advances in MS technology, and it is easily overlooked that significant progress has been made in the design of novel cross-linking reagents. In this review, the advent of cleavable cross-linking reagents will be highlighted. In particular, gas-phase (MS-) cleavable cross-linkers offer unique properties for an automated, data-dependent assignment of cross-linked products based on the generation of characteristic fragment ion signatures in MS/MS and MS3 spectra. Therefore, MS-cleavable cross-linkers are envisioned to hold the key for proteome-wide applications of the chemical cross-linking/MS approach, not only to delineate the conformation of single proteins but also to decipher protein interaction networks.