Recent CMI User Publications

Rovere M, Powers AE, Jiang H, Pitino JC, Fonseca-Ornelas L, Patel DS, Achille A, Langen R, Varkey J, Bartels T. E46K-like α-synuclein mutants increase lipid interactions and disrupt membrane selectivity. J Biol Chem 2019;294(25):9799-9812.Abstract
Parkinson's disease (PD) is one of the most common neurodegenerative disorders, and both genetic and histopathological evidence have implicated the ubiquitous presynaptic protein α-synuclein (αSyn) in its pathogenesis. Recent work has investigated how disrupting αSyn's interaction with membranes triggers trafficking defects, cellular stress, and apoptosis. Special interest has been devoted to a series of mutants exacerbating the effects of the E46K mutation (associated with autosomal dominant PD) through homologous Glu-to-Lys substitutions in αSyn's N-terminal region ( E35K and E61K). Such E46K-like mutants have been shown to cause dopaminergic neuron loss and severe but L-DOPA-responsive motor defects in mouse overexpression models, presenting enormous translational potential for PD and other "synucleinopathies." In this work, using a variety of biophysical techniques, we characterize the molecular pathology of E46K-like αSyn mutants by studying their structure and membrane-binding and remodeling abilities. We find that, although a slight increase in the mutants' avidity for synaptic vesicle-like membranes can be detected, most of their deleterious effects are connected to their complete disruption of αSyn's curvature selectivity. Indiscriminate binding can shift αSyn's subcellular localization away from its physiological interactants at the synaptic bouton toward trafficking vesicles and organelles, as observed in E46K-like cellular and murine models, as well as in human pathology. In conclusion, our findings suggest that a loss of curvature selectivity, rather than increased membrane affinity, could be the critical dyshomeostasis in synucleinopathies.
Watanabe A, McCarthy KR, Kuraoka M, Schmidt AG, Adachi Y, Onodera T, Tonouchi K, Caradonna TM, Bajic G, Song S, McGee CE, Sempowski GD, Feng F, Urick P, Kepler TB, Takahashi Y, Harrison SC, Kelsoe G. Antibodies to a Conserved Influenza Head Interface Epitope Protect by an IgG Subtype-Dependent Mechanism. Cell 2019;177(5):1124-1135.e16.Abstract
Vaccines to generate durable humoral immunity against antigenically evolving pathogens such as the influenza virus must elicit antibodies that recognize conserved epitopes. Analysis of single memory B cells from immunized human donors has led us to characterize a previously unrecognized epitope of influenza hemagglutinin (HA) that is immunogenic in humans and conserved among influenza subtypes. Structures show that an unrelated antibody from a participant in an experimental infection protocol recognized the epitope as well. IgGs specific for this antigenic determinant do not block viral infection in vitro, but passive administration to mice affords robust IgG subtype-dependent protection against influenza infection. The epitope, occluded in the pre-fusion form of HA, is at the contact surface between HA head domains; reversible molecular "breathing" of the HA trimer can expose the interface to antibody and B cells. Antigens that present this broadly immunogenic HA epitope may be good candidates for inclusion in "universal" flu vaccines.
Rogers JM, Waters CT, Seegar TCM, Jarrett SM, Hallworth AN, Blacklow SC, Bulyk ML. Bispecific Forkhead Transcription Factor FoxN3 Recognizes Two Distinct Motifs with Different DNA Shapes. Mol Cell 2019;74(2):245-253.e6.Abstract
Transcription factors (TFs) control gene expression by binding DNA recognition sites in genomic regulatory regions. Although most forkhead TFs recognize a canonical forkhead (FKH) motif, RYAAAYA, some forkheads recognize a completely different (FHL) motif, GACGC. Bispecific forkhead proteins recognize both motifs, but the molecular basis for bispecific DNA recognition is not understood. We present co-crystal structures of the FoxN3 DNA binding domain bound to the FKH and FHL sites, respectively. FoxN3 adopts a similar conformation to recognize both motifs, making contacts with different DNA bases using the same amino acids. However, the DNA structure is different in the two complexes. These structures reveal how a single TF binds two unrelated DNA sequences and the importance of DNA shape in the mechanism of bispecific recognition.
Silva CM, Ferguson FM, Cai Q, Donovan KA, Nandi G, Patnaik D, Zhang T, Huang H-T, Lucente DE, Dickerson BC, Mitchison TJ, Fischer ES, Gray NS, Haggarty SJ. Targeted degradation of aberrant tau in frontotemporal dementia patient-derived neuronal cell models. Elife 2019;8Abstract
Tauopathies are neurodegenerative diseases characterized by aberrant forms of tau protein accumulation leading to neuronal death in focal brain areas. Positron emission tomography (PET) tracers that bind to pathological tau are used in diagnosis, but there are no current therapies to eliminate these tau species. We employed targeted protein degradation technology to convert a tau PET-probe into a functional degrader of pathogenic tau. The hetero-bifunctional molecule QC-01-175 was designed to engage both tau and Cereblon (CRBN), a substrate-receptor for the E3-ubiquitin ligase CRL4, to trigger tau ubiquitination and proteasomal degradation. QC-01-175 effected clearance of tau in frontotemporal dementia (FTD) patient-derived neuronal cell models, with minimal effect on tau from neurons of healthy controls, indicating specificity for disease-relevant forms. QC-01-175 also rescued stress vulnerability in FTD neurons, phenocopying CRISPR-mediated -knockout. This work demonstrates that aberrant tau in FTD patient-derived neurons is amenable to targeted degradation, representing an important advance for therapeutics.
Zheng S, Abreu N, Levitz J, Kruse AC. Structural basis for KCTD-mediated rapid desensitization of GABA signalling. Nature 2019;567(7746):127-131.Abstract
The GABA (γ-aminobutyric acid type B) receptor is one of the principal inhibitory neurotransmitter receptors in the brain, and it signals through heterotrimeric G proteins to activate a variety of effectors, including G-protein-coupled inwardly rectifying potassium channels (GIRKs). GABA-receptor signalling is tightly regulated by auxiliary subunits called KCTDs, which control the kinetics of GIRK activation and desensitization. However, the mechanistic basis for KCTD modulation of GABA signalling remains incompletely understood. Here, using a combination of X-ray crystallography, electron microscopy, and functional and biochemical experiments, we reveal the molecular details of KCTD binding to both GABA receptors and G-protein βγ subunits. KCTDs associate with the receptor by forming an asymmetric pentameric ring around a region of the receptor carboxy-terminal tail, while a second KCTD domain, H1, engages in a symmetric interaction with five copies of Gβγ in which the G-protein subunits also interact directly with one another. We further show that KCTD binding to Gβγ is highly cooperative, defining a model in which KCTD proteins cooperatively strip G proteins from GIRK channels to induce rapid desensitization following receptor activation. These results provide a framework for understanding the molecular basis for the precise temporal control of GABA signalling by KCTD proteins.
Rovere M. Circular Dichroism and Isothermal Titration Calorimetry to Study the Interaction of α-Synuclein with Membranes. Methods Mol Biol 2019;1948:123-143.Abstract
α-Synuclein's physiology and pathology have been linked by numerous reports to its ability to bind and remodel membranes, especially at synaptic terminals. It is therefore critical for researchers investigating the determinants of these interactions to rely on methods capable of providing an accurate and complete physicochemical snapshot of the binding events. Circular dichroism (CD) and isothermal titration calorimetry (ITC) are established techniques for the study of binding equilibria in biological systems and, especially when used in combination, allow a thorough characterization of the protein-lipid interplay.Here we provide general guidelines and describe some common pitfalls of these experiments. This protocol describes the preparation of small unilamellar vesicles (SUVs), mimicking the curved bilayers α-synuclein normally interacts with, the CD-monitored titration of α-synuclein with SUVs, the ITC (lipid-into-protein) experiment, and the subsequent data analysis using an n independent binding site model.
Lee S-J, Tran NQ, Lee J, Richardson CC. Hydrophobic Residue in Escherichia coli Thioredoxin Critical for the Processivity of T7 DNA Polymerase. Biochemistry 2018;57(40):5807-5817.Abstract
Bacteriophage T7 uses the thioredoxin of its host, Escherichia coli, to enhance the processivity of its DNA polymerase, a requirement for the growth of phage T7. The evolutionarily conserved structure and high degree of homology of amino acid sequence of the thioredoxin family imply that homologues from other organisms might also interact with T7 DNA polymerase to support the phage growth. Despite the structural resemblance, human thioredoxin, whose X-ray crystallographic structure overlaps with that of the E. coli protein, cannot support T7 phage growth. It does not form a complex with T7 DNA polymerase as determined by surface plasmon resonance and thus does not increase the processivity. Homologous scanning analysis using this nonfunctional homologue reveals that the 60 N-terminal and the 12 C-terminal amino acid residues of E. coli thioredoxin can be substituted for its human counterpart without significantly affecting phage growth. Comparison of chimeric thioredoxins, followed by site-directed mutagenesis, identifies leucine 95 as a critical element. This residue may contribute to hydrophobic interactions with the thioredoxin-binding loop of the polymerase; levels of DNA binding and thus nucleotide polymerization are significantly decreased in the absence of this residue. The results suggest that the specific interactions at the interface of thioredoxin and DNA polymerase, rather than the overall structure, are important in the interactions that promote high processivity.
Wang L, Fu T-M, Zhou Y, Xia S, Greka A, Wu H. Structures and gating mechanism of human TRPM2. Science 2018;362(6421)Abstract
Transient receptor potential (TRP) melastatin 2 (TRPM2) is a cation channel associated with numerous diseases. It has a C-terminal NUDT9 homology (NUDT9H) domain responsible for binding adenosine diphosphate (ADP)-ribose (ADPR), and both ADPR and calcium (Ca) are required for TRPM2 activation. Here we report cryo-electron microscopy structures of human TRPM2 alone, with ADPR, and with ADPR and Ca NUDT9H forms both intra- and intersubunit interactions with the N-terminal TRPM homology region (MHR1/2/3) in the apo state but undergoes conformational changes upon ADPR binding, resulting in rotation of MHR1/2 and disruption of the intersubunit interaction. The binding of Ca further engages transmembrane helices and the conserved TRP helix to cause conformational changes at the MHR arm and the lower gating pore to potentiate channel opening. These findings explain the molecular mechanism of concerted TRPM2 gating by ADPR and Ca and provide insights into the gating mechanism of other TRP channels.
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