Cross-linking mass spectrometry (XL-MS) has matured into a potent tool to identify protein-protein interactions or to uncover protein structures in living cells, tissues, or organelles. The unique ability to investigate the interplay of proteins within their native environment delivers valuable complementary information to other advanced structural biology techniques. This Review gives a comprehensive overview of the current possible applications as well as the remaining limitations of the techn ...[more]
Project description:Chemical-Crosslinking Mass Spectrometry (XLMS) using MS-cleavable crosslinkers is fast becoming an established technique in the study of protein-protein interactions for both small and large scale samples. With the increased uptake of XLMS as a technique, different combinations of crosslinker types, fragmentation strategies and analysis programs are being applied to a diverse array of biological samples. This study is focused on understanding how the three variables of an XLMS experiment – crosslinker type, fragmentation and program – could generate differences in identifications, leading to increased biological coverage of a sample. Here we probe for the first time, the known enzyme:substrate interaction between yeast arginine methyltransferase Hmt1p and its substrate, heterologous nucleolar protein Npl3p. We use this known interaction as a platform to compare two analysis programs, MeroX and XlinkX2.0, using two crosslinker types, DSSO and DSBU, and two mass-spectrometry fragmentation strategies, CID/ETD and SteppedHCD. Through these we also compare different algorithm strategies, Precursor and Reporter-Ion, as well as assess the impact of restricting data searches to lysine only crosslinks versus the inclusion of serine, threonine and tyrosine as reactive residues. From this analysis we show direct evidence of Hmt1p in contact with its known methylation sites on Npl3p, the intrinsically disordered “SRGG” region. We also show through our multi-crosslinker, multi-fragmentation and multi-software approach that two approaches leads to greater understanding and depth of a crosslinked sample, and this is due to some combinations of experimental variables creating greater coverage of crosslinks than others.
Project description:We have created a synthetic crosslinked peptide library to benchmark crosslinking mass spectrometry search engines. The unique benefit of the library is knowing which identified crosslinks are true and which are false. The data collected from mass spectrometry measurements of the peptide library were used to assess the most frequently used search algorithms. The datasets included will provide an important resource for the crosslinking community to evaluate and optimise search engines, results from which have far-reaching implications.
Project description:Cross-linking of BSA with a novel cross-linker. Modification of the cross-linker containing peptides with CuAAC-chemistry to attach a cleavable biotin-derivative. Enrichment with streptavidin-beads.
Project description:Cross-linking mass spectrometry (XLMS) is becoming increasingly popular, and current advances are widening the applicability of the technique so that it can be utilized by non-specialist laboratories. Specifically, the use of novel mass spectrometry-cleavable (MS-cleavable) reagents dramatically reduces complexity of the data by providing i) characteristic reporter ions and ii) the mass of the individual peptides, rather than that of the cross-linked moiety. However, optimum acquisition strategies to obtain the best quality data for such cross-linkers with higher energy C-trap dissociation (HCD) alone is yet to be achieved. Therefore, we have carefully investigated and optimized MS parameters to facilitate the identification of disuccinimidyl sulfoxide (DSSO)-based cross-links on HCD-equipped mass spectrometers. From the comparison of 9 different fragmentation energies we chose several stepped- HCD fragmentation methods that were evaluated on a variety of cross-linked proteins. The optimal stepped-HCD method was then directly compared with previously described methods using an Orbitrap Fusion™ Lumos™ Tribrid™ instrument using a high-complexity sample. The final results indicate that our stepped-HCD method is able to identify more cross-links than other methods, mitigating the need for multistage MS (MSn) enabled instrumentation and alternative dissociation techniques.
Project description:Cleavage factor II (CF II) is a poorly characterized component of the multi-protein complex catalyzing 3' cleavage and polyadenylation of mammalian mRNA precursors. We have reconstituted CF II as a heterodimer of hPcf11 and hClp1. The heterodimer is active in partially reconstituted cleavage reactions, whereas hClp1 by itself is not. Pcf11 moderately stimulates the RNA 5' kinase activity of hClp1; the kinase activity is dispensable for RNA cleavage. CF II binds RNA with nanomolar affinity. Binding is mediated mostly by the two zinc fingers in the C-terminal region of hPcf11. RNA is bound without pronounced sequence-specificity, but extended G-rich sequences appear to be preferred. We discuss the possibility that CF II contributes to the recognition of cleavage/polyadenylation substrates through interaction with G-rich far-downstream sequence elements.
Project description:We provide a cross-linking/MS workflow that can be applied to complex systems. The software tool MeroX 2.0 can be used to identify cross-linked peptide on a proteome-wide level. We applied the workflow to extracts of Drosophila embryos and identified 5,129 unique cross-linked residue pairs in biological triplicates.
Project description:To investigate the structural basis of SurA’s chaperone function, we characterized crosslinks between it and two of its clients, OmpA and OmpX, and used those as distance restraints to build structural models.
Project description:Human condensin I and condensin II complexes play essential roles in chromatin condensation during the cell division process. Both complexes use ATP as the energy source to pack extended chromatin into the short form of chromosome. In order to understand the mechanism of their function, we performed cross-linking mass spectrometry (XL-MS) analyses of both complexes and mapped the inter-molecular and intra-molecular interactions of the subunits.
Project description:Herpesviruses are an ancient family of highly-prevalent human and animal pathogens that acquire their membrane envelopes in the cytoplasm of infected cells. While multiple conserved viral proteins are known to be required for efficient herpesvirus production, many of these proteins lack identifiable structural homologues and the molecular details of herpesvirus assembly remain unclear. We have characterized the complex of assembly proteins pUL7 and pUL51 from herpes simplex virus (HSV)-1, an α-herpesvirus, using multi-angle light scattering and small-angle X-ray scattering with chemical crosslinking. HSV-1 pUL7 and pUL51 form a stable 1:2 complex that is capable of higher-order oligomerization in solution. We solved the crystal structure of this complex, revealing a core heterodimer comprising pUL7 bound to residues 41–125 of pUL51. While pUL7 adopts a previously-unseen compact fold, the extended helix-turn-helix conformation of pUL51 resembles the cellular endosomal complex required for transport (ESCRT)- III component CHMP4B, suggesting a direct role for pUL51 in promoting membrane scission during virus assembly. We demonstrate that the interaction between pUL7 and pUL51 homologues is conserved acrosshuman α-, β- and γ-herpesviruses, as is their association with trans-Golgi membranes in cultured cells. However, pUL7 and pUL51 homologues do not form complexes with their respective partners from different virus families, suggesting that the molecular details of the interaction interface have diverged. Our results demonstrate that the pUL7:pUL51 complex is conserved across the herpesviruses and provide a structural framework for understanding its role in herpesvirus assembly.