CIISB Research Highlights Archive

LEDGF/p75 IBD binding partners interact in a structurally conserved manner. Solution structures of the IBD in complex with the binding motifs from POGZ, JPO2 motif 1 and 2 (M1, M2), IWS1, and MLL1 determined by NMR spectroscopy.

Zeger Debyser and Václav Veverka Research Groups

Significance

The transcription coactivator LEDGF/p75 contributes to regulation of gene expression by tethering other factors to actively transcribed genes on chromatin. Its chromatin-tethering activity is hijacked in two important disease settings, HIV and mixed-lineage leukemia; however, the basis for the biological regulation of LEDGF/p75’s interaction to binding partners has remained unknown. This has represented a gap in our understanding of LEDGF/p75’s fundamental biological function and a major limitation for development of therapeutic targeting of LEDGF/p75 in human disease. Our work provides a mechanistic understanding of how the lens epithelium-derived growth factor interaction network is regulated at the molecular level. We reveal that structurally conserved IBD-binding motifs (IBMs) on known LEDGF/p75 binding partners can be regulated by phosphorylation, permitting switching between low- and high-affinity states. Finally, we show that elimination of IBM phosphorylation sites on MLL1 disrupts the oncogenic potential of primary MLL1-rearranged leukemic cells. Our results demonstrate that kinase-dependent phosphorylation of MLL1 represents a previously unknown oncogenic dependency that may be harnessed in the treatment of MLL-rearranged leukemia.

Sharma, S. et. al.: Affinity switching of the LEDGF/p75 IBD interactome is governed by kinase-dependent phosphorylation, PNAS 2018, 115 (30) E7053-E7062.doi.org/10.1073/pnas.1803909115

Interaction of TBEV virions with Fab fragments of neutralizing antibody 19/1786. a Cryo-EM micrograph of TBEV virions incubated with Fab fragments of 19/1786. Scale bar represents 100 nm. b Electron-density map of Fab-covered TBEV virion. c Molecular surface of TBEV virion covered with Fab 19/1786 fragments low-pass filtered to 7 Å resolution. E-proteins are shown in red, green, and blue. Fab fragments are shown in magenta (heavy chain) and pink (light chain). Scale bars in band c represent 10 nm. d Footprints of Fab 19/1786 on TBEV surface. e The Fab 19/1786 binds to the domain III at an angle of 135° relative to the axis of the E-protein ectodomain.

Pavel Plevka Research group

Significance

Tick-borne encephalitis virus (TBEV) causes 13,000 cases of human meningitis and encephalitis annually. However, the structure of the TBEV virion and its interactions with antibodies are unknown. Here, Pavel Plevka and his coworkers present cryo-EM structures of the native TBEV virion and its complex with Fab fragments of neutralizing antibody 19/1786. Flavivirus genome delivery depends on membrane fusion that is triggered at low pH. The virion structure indicates that the repulsive interactions of histidine side chains, which become protonated at low pH, may contribute to the disruption of heterotetramers of the TBEV envelope and membrane proteins and induce detachment of the envelope protein ectodomains from the virus membrane. The Fab fragments bind to 120 out of the 180 envelope glycoproteins of the TBEV virion. Unlike most of the previously studied flavivirus-neutralizing antibodies, the Fab fragments do not lock the E-proteins in the native-like arrangement, but interfere with the process of virus-induced membrane fusion. 

Füzik, T. et al. Structure of tick-borne encephalitis virus and its neutralization by a monoclonal antibody. Nature Communications 9, 11, doi:10.1038/s41467-018-02882-0 (2018)

Structure of PHL complex with propargyl a-l-fucoside. (A) PHL monomer (chain A) overall architecture with propargyl a-l-fucoside shown as magenta sticks. Individual binding sites are labelled in black (front plane) or grey (back plane) (B) Side view of PHL dimer with chain B shown in grey and without ligands. (C) Individual PHL fucose‐type binding sites with Compound 5 (magenta) bound. Amino acids responsible in ligand binding are highlighted and labelled. (D) PHL galactose‐type binding site with propargyl a-l-fucoside (magenta) bound and PHL galactose‐type binding site with d‐Gal (yellow) bound (PDB ID 5MXH). Colour code for panels C/D: amino acids involved in ligand‐binding through H‐bond=cyan, CH–π interaction=orange, or water bridge=grey.

Michaela Wimmerova Research Group

Significance

Photorhabdus asymbiotica is a gram‐negative bacterium that is not only as effective an insect pathogen as other members of the genus, but it also causes serious diseases in humans. The recently identified lectin PHL from P. asymbiotica verifiably modulates an immune response of humans and insects, which supports the idea that the lectin might play an important role in the host–pathogen interaction. Dimeric PHL contains up to seven l‐fucose‐specific binding sites per monomer, and in order to target multiple binding sites of PHL, α‐l‐fucoside‐containing di‐, tri‐ and tetravalent glycoclusters were synthesized. The interaction between fucoside derivates and PHL was investigated by several biophysical and biological methods, ITC and SPR measurements, hemagglutination inhibition assay, and an investigation of bacterial aggregation properties were carried out. Details of the interaction between PHL and propargyl α‐l‐fucoside as a monomer unit were revealed using X‐ray crystallography. Besides this, the interaction with multivalent compounds was studied by NMR techniques. The newly synthesized multivalent fucoclusters proved to be up to several orders of magnitude better ligands than the natural ligand, l‐fucose.

Jancarikova, G. et al. Synthesis of a-l-Fucopyranoside-Presenting Glycoclusters and Investigation of Their Interaction with Photorhabdus asymbiotica Lectin (PHL). Chemistry – A European Journal, 24, 4055-4068, doi.org/10.1002/chem.201705853

Automated structure determination using 4D-CHAINS/autoNOE-Rosetta. (a) Logo of 4D-CHAINS algorithm depicting its powerfulness. Chains squeeze the NMR spectrometer to unleash high-quality structures by using a minimal set of 4D spectra and fully automated data analysis. (b) 4D-CHAINS utilizes two complementary experimental datasets, a 4D-TOCSY and a 4D-NOESY, to yield correct assignments for at least 95% of residues and an error rate of less than 1.5% (middle bar; TOCSY-NOESY). (c-d) Performance of different 4D-CHAINS assignment scenarios for a 20 kDa protein structure, α-lytic protease, calculated using autoNOE-Rosetta. (c) Goodness of structure ensembles is measured using the Rosetta all-atom energy function, backbone heavy atom RMSD to X-ray structure and degree of structural convergence. (d) Lowest-energy structures in each ensemble colored as the points in (c) superimposed on the X-ray reference structure (gray).

Konstantinos Tripsianes Research Group

Significance

The automation of NMR structure determination remains a significant bottleneck towards increasing the throughput and accessibility of NMR as a structural biology tool to study proteins. The chief barrier currently is that obtaining NMR assignments at sufficient levels of completeness to accurately define the structures by conventional methods requires a significant amount of spectrometer time (several weeks), and effort by a trained expert (up to several months). Here, we describe 4D-CHAINS/autoNOE-Rosetta, a complete pipeline for NOE-driven structure determination of medium- to larger-sized proteins. The 4D-CHAINS algorithm analyzes two 4D spectra in an iterative ansatz where common NOEs between different spin systems supplement conventional through-bond connectivities to establish assignments of sidechain and backbone resonances at high levels of completeness and with a minimum error rate. The 4D-CHAINS assignments are then used to guide automated assignment of long-range NOEs and structure refinement in autoNOE-Rosetta. Our results on four targets ranging in size from 15.5 to 27.3 kDa illustrate that the NMR structures of proteins can be determined accurately and in an unsupervised manner in a matter of days.

4D-CHAINS software is free for non-commercial usage and can be downloaded from https://github.com/tevang/4D-CHAINS

Evangelidis, T. et al. Automated NMR resonance assignments and structure determination using a minimal set of 4D spectra. Nature Communications 9, 13, doi:10.1038/s41467-017-02592-z (2018).

Schematic of an intramolecular A) i-motif DNA structure and B) C.C+ base pair. C) Double-staining (PI/FAM) FCM analysis of transfected HeLa cells with the (FAM)-DAP construct (upper left corner). Percentages of viable DNA non-transfected cells, viable DNA-containing cells, non-transfected dead/compromised cells, and transfected dead/compromised cells with DNA are indicated in left-bottom, right-bottom, left-top, and right-top quadrants, respectively. Confocal microscope images of cells transfected with (FAM)-DAP (upper right corner). The green color indicates the localization of (FAM)-DAP. The blue color corresponds to a cell nucleus stained by Hoechst 33342. Imino region of 1D 1H NMR spectra of DAP in vitro in T-buffer (140 mm sodium phosphate, 5 mm KCl, 10 mm MgCl2, pH 7.0) (black) and in-cell (red). Imino region of 1D 1H NMR spectrum of extracellular fluid taken from the in-cell NMR samples after completion of the spectra acquisition (gray). The (in-cell) NMR spectra were acquired at 20oC.

Lukáš Trantírek Research Group

Significance

C-rich DNA has the capacity to form a tetra-stranded structure known as an i-motif. The i-motifs within genomic DNA have been proposed to contribute to the regulation of DNA transcription. However, direct experimental evidence for the existence of these structures in vivo has been missing. Whether i-motif structures form in complex environment of living cells is not currently known. Using state-of- the-art in-cell NMR spectroscopy, Lukáš Trantírek and his colleagues from CEITEC Masaryk University in Brno has evaluated the stabilities of i-motif structures in the complex cellular environment. They showed that i-motifs formed from naturally occurring C-rich sequences in the human genome are stable and persist in the nuclei of living human cells. The obtained data show that i-motif stabilities in vivo are generally distinct from those in vitro. Results are the first to interlink the stability of DNA i-motifs in vitro with their stability in vivo and provide essential information for the design and development of i-motif-based DNA biosensors for intracellular applications.

Dzatko, S.; Krafcikova, M.; Hänsel-Hertsch, R.; Fessl, T.; Fiala, R.; Loja, T.; Krafcik, D.; Mergny, J.-L.; Foldynova-Trantirkova, S. & Trantirek, L.: Evaluation of the Stability of DNA i-Motifs in the Nuclei of Living Mammalian Cells, Angew. Chem. Int. Edit. 2018, in press, DOI: 10.1002/anie.201712284

Cryo-EM Structures of Polyproline-Stalled Ribosomes in the Presence of EF-P (A-C) Schematic representation (A) and cryo-EM reconstructions (B and C) of PPP-stalled ribosome complexes with (B) or without (C) of EF-P (salmon) bound in the E site. (D and E) Cryo-EM density (mesh) of the CCA end of the P-site tRNA (green) from cryo-EM maps in (C) without EF-P (D) and in (B) with EF-P (E), respectively, with aligned fMet (cyan, PDB: 1VY4) (Polikanov et al., 2014).

Daniel N. Wilson Research Group

Significance

Ribosomes synthesizing proteins containing consecutive proline residues become stalled and require rescue via the action of uniquely modified translation elongation factors, EF-P in bacteria, or archaeal/eukaryotic a/eIF5A. To date, no structures exist of EF-P or eIF5A in complex with translating ribosomes stalled at polyproline stretches, and thus structural insight into how EF-P/eIF5A rescue these arrested ribosomes has been lacking. Here we present cryo-EM structures of ribosomes stalled on proline stretches, without and with modified EF-P. The structures suggest that the favored conformation of the polyproline-containing nascent chain is incompatible with the peptide exit tunnel of the ribosome and leads to destabilization of the peptidyl-tRNA. Binding of EF-P stabilizes the P-site tRNA, particularly via interactions between its modification and the CCA end, thereby enforcing an alternative conformation of the polyproline-containing nascent chain, which allows a favorable substrate geometry for peptide bond formation.

Huter, P.; Arenz, S.; Bock, L. V.; Frister, J. O.; Heuer, A.; Peil, L.; Starosta, A. L.; Peske, F.; Nováček, J.; Berninghausen, O.; Grubmüller, H.; Tenson, T.; Beckmann, R.; Rodina, M. V.; Vaiana, A. C. & Wilson, D. N.: Structural Basis for Polyproline-Mediated Ribosome Stalling and Rescue by the Translation Elongation Factor EF-P, Moll Cell 68, No. 3., 515-527.e6 DOI: dx.doi.org/10.1016/j.molcel.2017.10.014