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Cross-linking mass spectrometry uncovers protein interactions and functional assemblies in synaptic vesicle membranes

ABSTRACT: Synaptic vesicles are storage organelles for neurotransmitters in the pre-synaptic cytosol. When an action potential arrives at the pre-synaptic terminal, they fuse with the pre-synaptic membrane and neurotransmitters are released. In this project, we set out to study the protein interactions formed in synaptic vesicle membranes. For this, we first assessed the proteome of five independent vesicle preparations. Using chemical cross-linking, we then tackled the interactions of the major protein components. To gain further insights, we combined this approach with a chemical labelling strategy. Specific protein interactions were then studied after (i) treating the vesicles with Botulinum neurotoxin B, (ii) binding the soluble SNARE complex, and (iii) fusion of the vesicles with empty liposomes. Our findings reveal stable interaction modules in synaptic vesicles.

INSTRUMENT(S): Orbitrap Fusion, Q Exactive Plus

ORGANISM(S): Rattus Norvegicus (rat)

TISSUE(S): Brain

SUBMITTER: Marie Alfes

LAB HEAD: Carla Schmidt

PROVIDER: PXD020859 | Pride | 2020-12-09

REPOSITORIES: Pride

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Mass Spectrometry Uncovers Protein Interactions and Stoichiometry of Intermediates and Sub-complexes for SNARE Complex Assembly

Project description:The neuronal SNARE complex assembles from vesicular Synaptobrevin-2 as well as Syntaxin-1 and SNAP25 anchored to the presynaptic membrane. It mediates fusion of synaptic vesicles with the presynaptic plasma membrane resulting in exocytosis of neurotransmitters into the synaptic cleft. While the general sequence of SNARE complex formation is well-established, our knowledge on possible intermediates is still incomplete. We, therefore, follow the step-wise assembly of the SNARE complex and target individual SNAREs, binary sub-complexes, the ternary SNARE complex as well as interactions with Complexin-1. Using native mass spectrometry, we identify the stoichiometry of preferred sub-complexes and monitor oligomerisation of various assemblies. Importantly, we find that interactions with Complexin-1 reduce self-association of the ternary SNARE complex. Chemical cross-linking provides detailed insights into these interactions suggesting a role during membrane fusion. Taken together, we unravel possible intermediates and preferred sub-complexes and compile a road map of SNARE complex assembly including regulation by Complexin-1.

2023-01-25 | PXD030619 | Pride

Beta-synuclein potentiates synaptic vesicle dopamine uptake and rescues dopaminergic neurons from MPTP-induced death in the absence of other synucleins

Project description:Previous studies have demonstrated an importance of alpha-synuclein as a modulator of various mechanisms implicated in chemical neurotransmission but information about other two synuclein family members’ involvement in molecular processes taking place in presynaptic terminals is limited. Here we demonstrated that dopamine uptake by synaptic vesicles isolated from the striatum of mice lacking beta-synuclein was significantly reduced. Reciprocally, reintroduction, either in vivo or in vitro, of beta-synuclein but not alpha- or gamma-synuclein improved uptake by vesicles isolated from the striatum of triple alpha/beta/gamma-synuclein deficient mice. Proteomic analysis of synuclein-free and beta-synuclein-only-containing synaptic vesicles suggested that mechanistically, beta-synuclein potentiates vesicular monoamine transporter 2 (VMAT2)-dependent dopamine uptake by assembling specific multiprotein complexes comprised of resident vesicular proteins and transiently associated, predominantly cytosolic proteins. The increased availability of such complexes on the surface of striatal synaptic vesicles lacking other synucleins should also promote sequestration of 1-methyl-4-phenylpyridinium (MPP+), a toxic metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which explains the resistance of dopaminergic neurons of substantia nigra lacking alpha-synuclein and/or gamma-synuclein to this neurotoxin.

2022-02-17 | PXD027786 | Pride

Capturing protein communities by structural proteomics in a thermophilic eukaryote

Project description:The arrangement of proteins into complexes is a key organizational principle for many cellular functions. Although the topology of many complexes has been systematically analyzed in isolation, their molecular sociology in situ remains elusive. Here, we show that crude cellular extracts of a eukaryotic thermophile, Chaetomium thermophilum, retain basic principles of cellular organization. Using a structural proteomics approach, we simultaneously characterized the abundance, interactions and structure of a third of the C. thermophilum proteome within these extracts. We identified 27 distinct protein communities that include 108 interconnected complexes, which dynamically associate with each other and functionally benefit from being in close proximity in the cell. Furthermore, we investigated the structure of fatty acid synthase within these extracts by cryoEM and this revealed multiple, flexible states of the enzyme in adaptation to its association with other complexes, thus exemplifying the need for in situ studies. As the components of the captured protein communities are known – at both the protein and complex level – this study constitutes another step forward towards a molecular understanding ofsubcellular organization.

2017-07-26 | PXD006626 | Pride

Crosslinking mass spectrometry of yeast Pol I pre-initiation complex

Project description:In eukaryotic cells, ribosomal RNA is transcribed by RNA polymerase I (Pol I). To initiate transcription, Pol I requires the assembly of a multi-subunit pre-initiation complex (PIC). In yeast, the minimal PIC includes Pol I, the transcription factor Rrn3 and Core Factor (CF) composed of subunits Rrn6, Rrn7 and Rrn11. We have determined the cryo-EM structure of a 18-subunit yeast Pol I complex together with CF, Rrn3 and transcription scaffold. To aid in modeling the structure based on the cryo-EM map, we performed crosslinking mass spectrometry.

2017-07-31 | PXD006510 | Pride

TRIM72 cross-linked by the higher-order assembly on the negatively charged liposome surface

Project description:Plasma membrane repair is a rapid cellular response for resealing of membrane for cell survival. In the early step of repair process, TRIM72 is known to a key initiator for facilitating patch membrane to the damaged membrane site. When acute membrane injury happens, TRIM72 is also known to sensitively generate disulfide bonds formations by reactive oxygen species and further oligomerize with each other. We tried to clarify this repair system using in vitro reconstruction of TRIM72-liposome complex and find critical sites using cross-linker mass spectrometry. Using each four different length of sulfhydryl reactive cross-linkers, TRIM72 cross-linked with each other on the negatively charged liposome surface only. We also identified that the cross-linking bridges were highly conserved except bismaleimidoethane as a shortest arm length about 8 Å only. Our results indicated that the B2-box/B2-box locates closely with each other on the liposome surface. Furthermore, freely open RING domain is rearranged into the specific conformation, where located near the H2 helix of coiled coil domain. It suggests that the conformational changes of TRIM72 are induced by higher order assembly on the negative charged membrane surface.

2024-01-26 | PXD024946 | Pride

Biochemically validated structural model of the 15-subunit intraflagellar transport complex IFT-B

Project description:Cilia are ubiquitous eukaryotic organelles impotant for cellular motility, signaling, and sensory reception. Cilium formation requires intraflagellar transport of structural and signaling components and involves 22 different proteins organized into intraflagellar transport (IFT) complexes IFT-A and IFT-B that are transported by molecular motors. The IFT-B complex constitutes the backbone of polymeric IFT trains carrying cargo between the cilium and the cell body. Currently, high-resolution structures are only available for smaller IFT-B subcomplexes leaving > 50% structurally uncharacterized. Here, we used Alphafold to structurally model the 15-subunit IFT-B complex. The model was validated using cross-linking/mass-spectrometry data on reconstituted IFT-B complexes, X-ray scattering in solution, diffraction from crystals as well as site-directed mutagenesis and protein-binding assays. The IFT-B structure reveals an elongated and highly flexible complex consistent with cryo-electron tomographic reconstructions of IFT trains. The IFT-B complex organizes into IFT-B1 and IFT-B2 parts with binding sites for ciliary cargo and the inactive IFT dynein motor, respectively. Interestingly, our results are consistent with two different binding sites for IFT81/74 on IFT88/70/52/46 suggesting the possibility of different structural architectures for the IFT-B1 complex. Our data present a structural framework to understand IFT-B complex assembly, function, and ciliopathy variants.

2022-12-02 | PXD037049 | Pride

Altered Domain Structure of the Prion Protein Caused by Cu2+ Binding and Functionally Relevant Mutations: Analysis by Cross‐Linking, MS/MS, and NMR

Project description:The endogenous cellular prion protein (PrPC) can misfold into the scrapie isoform (PrPSc) and cause fatal infectious diseases. Despite significant research on the prion protein, both its normal function and whether alterations to that function play a critical role in prion diseases remain unknown. The protein consists of a predominantly alpha-helical C-terminal domain and an unstructured N-terminal domain that can coordinate Cu2+. Previous studies using NMR and EPR have revealed a tertiary association between the N-terminal domain and the C-terminal domain that we have hypothesized to be critical to the protein’s normal function. Here we investigated and quantified the inter-domain interactions within three different prion variants (wild type recombinant mouse PrPC, mutant delta central region (ΔCR), and disease mutant (E199K) after chemical cross-linking with a newly designed MS-cleavable reagent 1-(4-((2,5-Dioxopyrrolidin-1-yl)oxy)-4-oxobutyl)-4-(2-(3-methyl-3H-diazirin-3-yl)ethyl)-1,4-diazabicyclo[2.2.2] octane-1,4-diium (APDC4), followed by nHPLC(RP) and tandem MS analysis.

2020-06-16 | PXD012427 | Pride

Enabling Photoactivated Cross-linking Mass Spectrometric Analysis of Protein Complexes by Novel MS-cleavable Cross-linkers

Project description:Cross-linking mass spectrometry (XL-MS) is a powerful tool for studying protein-protein interactions and elucidating architectures of protein complexes. While residue-specific XL-MS studies have been very successful, accessibility of interaction regions non-targetable by specific chemistries remain difficult. Photochemistry has shown great potential in capturing those regions due to nonspecific reactivity, but low yields and high complexities of photocross-linked products have hindered their identification, limiting current studies predominantly to single proteins. Here, we describe the development of three novel MS-cleavable heterobifunctional cross-linkers, namely SDASO (Succinimidyl diazirine sulfoxide), to enable fast and accurate identification of photocross-linked peptides by MSn. The MSn-based workflow allowed SDASO XL-MS analysis of the yeast 26S proteasome, demonstrating the feasibility of photocross-linking of large protein complexes for the first time. Comparative analyses have revealed that SDASO cross-linking is robust and captures interactions complementary to residue-specific reagents, providing the foundation for future applications of photocross-linking in complex XL-MS studies.

2021-05-07 | PXD022690 | Pride

Architecture of the yeast Elongator complex

Project description:The highly conserved eukaryotic Elongator complex performs specific chemical modifications on wobble base uridines of tRNAs, which are essential for proteome stability and homeostasis. The complex is formed by six individual subunits (Elp1-6) that are all equally important for its tRNA modification activity. However, its overall architecture and the detailed reaction mechanism remain elusive. Here, we report the structures of the fully assembled yeast Elongator and the Elp123 sub-complex solved by an integrative structure determination approach showing that two copies of the Elp1, Elp2 and Elp3 subunits form a two-lobed scaffold, which binds Elp456 asymmetrically. Our topological models are consistent with previous studies on individual subunits and further validated by complementary biochemical analyses. Our study provides a structural framework on how the tRNA modification activity is carried out by Elongator.

2016-12-20 | PXD005251 | Pride

Reconstitution of mammalian Cleavage Factor II

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.

2020-05-26 | PXD010177 | Pride

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