Proteome-wide profiling of protein assemblies by cross-linking mass spectrometry

TLDR: An integrated workflow that robustly identifies cross-links from endogenous protein complexes in human cellular lysates is described, based on the application of mass spectrometry (MS)-cleavable cross-linkers, sequential collision-induced dissociation (CID)–tandem MS (MS/MS) and electron-transfer Dissociation (ETD)-MS/ MS acquisitions, and a dedicated search engine, XlinkX.

Abstract: A crosslinking-mass spectrometry strategy, including a new proteome database search engine called XlinkX, enables the identification of inter- and intra-protein cross-links in cell lysates on a proteome-wide scale. We describe an integrated workflow that robustly identifies cross-links from endogenous protein complexes in human cellular lysates. Our approach is based on the application of mass spectrometry (MS)-cleavable cross-linkers, sequential collision-induced dissociation (CID)–tandem MS (MS/MS) and electron-transfer dissociation (ETD)-MS/MS acquisitions, and a dedicated search engine, XlinkX, which allows rapid cross-link identification against a complete human proteome database. This approach allowed us to detect 2,426 unique cross-links at a 5% FDR (2,013 intraprotein and 413 interprotein cross-links) or 1,822 cross-links at a 1% FDR (1,622 intraprotein and 200 interprotein cross-links), indicating the detection of 326 or 134 protein-protein interactions at 5% FDR or 1% FDR, respectively, in HeLa cell lysates. We validated the confidence of our cross-linking results by using a target-decoy strategy and mapping the observed cross-link distances onto existing high-resolution structures. Our data provided new structural information about many protein assemblies and captured dynamic interactions of the ribosome in contact with different elongation factors.