Chemical crosslinking coupled with mass spectrometry (CXMS) has emerged as a powerful technique to obtain the dynamic conformations and interaction interfaces of protein complexes. Limited by the poor cell membrane permeability, chemical reactivity, and biocompatibility of crosslinkers, in vivo crosslinking to capture the dynamics of protein complexes with finer temporal resolution and higher coverage is attractive but challenging. In this work, a trifunctional crosslinker bis(succinimidyl) with propargyl tag (BSP), involving compact size, proper amphipathy, and enrichment capacity, was developed to enable better cell membrane permeability and efficient crosslinking in 5 min without obvious cellular interference. Followed by a two-step enrichment method based on click chemistry at the peptide level, 13,098 crosslinked peptides (5068 inter-crosslinked peptides and 8030 intra-crosslinked peptides) were identified under the data threshold of peptide-spectrum matches (PSMs) ≥2 on the basic of the FDR control of 1%, which was the most comprehensive dataset for homo species cells by a non-cleavable crosslinker. Besides, the interactome network comprising 1519 proteins connected by 2913 interaction edges in various intracellular compartments, as well as 80S ribosome structural dynamics, were characterized, showing the great potential of our in vivo crosslinking approach in minutes. All these results demonstrated that our developed BSP could provide a valuable toolkit for the in-depth in vivo analysis of protein–protein interactions (PPIs) and protein architectures with finer temporal resolution.
The protein structures and interactions that maintain and regulate cellular processes in different subcellular organelles are heterogeneous and dynamic. However, it remains challenging to characterize the subcellular specificity and translocation of protein complexes in terms of conformation and interactions. Herein, we developed a spatially resolved protein complex profiling approach by biocompatible chemical cross-linking in living cells (SPACX) to monitor the dynamics of protein conformation, interactions and translocation. The advancement of fast capturing protein complexes in the physiological state, coupled with efficient enrichment of the cross-linked peptides, ensured deep-coverage analysis of the protein interactome in living cells. By ensemble structure refinement with cross-linking restraints, subcellular-specific conformation heterogeneity was identified for PTEN. PTEN displayed a broader range of dynamic conformation changes on the dual specificity domains in the nucleus than in the cytoplasm. Moreover, based on conformational differences, different interacting assemblies involving 25 cytoplasm-exclusively and 18 nucleus-exclusively PTEN-interacting proteins were found to account for diverse biological functions. Upon ubiquitin-proteasome system (UPS) stress, the assembly of PTEN and its interacting partners changed obviously during translocation. We newly identified 36 PTEN-interacting proteins, which were found to be highly enriched in functional pathways closely related to cell apoptosis. Inspiringly, the interactions among PTEN isoforms and their interacting proteins were accessible by the determination of sequence-unique cross-linking interfaces for direct interactions. All these results indicate the promise of SPACX to elucidate the functional heterogeneity of proteins in individual subcellular sociology.
The transmembrane part of the S6 inner helix of the Kv1.2 potassium channel is a pivotal part in sustaining channel activity. However, the role of its extreme C-terminal end, which is located on the cytoplasmic side of the channel, is largely unknown. Here, we investigated the role of the extreme C-terminal end of the S6 inner helix (the HRET region) by constructing a series of C-terminal-truncated mutations related to this region in the C-terminal-truncated Kv1.2 channel. Mutations on Thr421 or Glu420 significantly altered the activation of the truncated channel. Mutations on Arg419 demonstrated that neutral or basic, but not acidic amino acid, is essential at the position for the truncated channel activation, and no functional channel was observed when the channel was truncated from His418. Hence, our results indicate that the extreme C-terminal end of the S6 inner helix plays an important regulatory role in the activation of the C-terminal-truncated Kv1.2 channel.
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