Giuliana Fusco

Direct observation of the three regions in α-synuclein that determine its membrane-bound behaviour

α-synuclein (αS) is a protein involved in neurotransmitter release in presynaptic terminals, and whose aberrant aggregation is associated with Parkinson’s disease. In dopaminergic neurons, αS exists in a tightly regulated equilibrium between water-soluble and membrane-associated forms. Here we used a combination of solid-state and solution-state NMR spectroscopy to characterize the conformations of αS bound to lipid membranes mimicking the composition and physical properties of synaptic vesicles. The study evidences three αS regions possessing distinct structural and dynamical properties, including an N-terminal helical segment having a role of membrane-anchor, an unstructured C-terminal region that is weakly associated with the membrane, and a central region acting as a sensor of the lipid properties and determining the affinity of αS membrane binding. Taken together, our data define the nature of the interactions of αS with biological membranes and provide insights into their roles in the function and in the molecular processes leading the aggregation of this protein.

Structural basis of membrane disruption and cellular toxicity by α-synuclein oligomers

A structural look at α-synuclein oligomers Fibrillar aggregates of the protein α-synuclein (αS) are the major constituents of Lewy bodies in Parkinsons disease. However, small oligomers that accumulate during the process of fibril formation are thought to cause the neuronal toxicity associated with the onset and progression of Parkinsons disease. Little is known about the detailed structural properties of αS oligomers and the molecular mechanisms that lead to their toxicity. Fusco et al. report the structural characterization of two forms of αS oligomers, which elucidates the fundamental structural elements giving rise to neuronal toxicity. Science, this issue p. 1440 Oligomers of α-synuclein generate neuronal damage when insertion of a highly structured core disrupts membrane integrity. Oligomeric species populated during the aggregation process of α-synuclein have been linked to neuronal impairment in Parkinson’s disease and related neurodegenerative disorders. By using solution and solid-state nuclear magnetic resonance techniques in conjunction with other structural methods, we identified the fundamental characteristics that enable toxic α-synuclein oligomers to perturb biological membranes and disrupt cellular function; these include a highly lipophilic element that promotes strong membrane interactions and a structured region that inserts into lipid bilayers and disrupts their integrity. In support of these conclusions, mutations that target the region that promotes strong membrane interactions by α-synuclein oligomers suppressed their toxicity in neuroblastoma cells and primary cortical neurons.

Conformational Recognition of an Intrinsically Disordered Protein

There is a growing interest in understanding the properties of intrinsically disordered proteins (IDPs); however, the characterization of these states remains an open challenge. IDPs appear to have functional roles that diverge from those of folded proteins and revolve around their ability to act as hubs for protein-protein interactions. To gain a better understanding of the modes of binding of IDPs, we combined statistical mechanics, calorimetry, and NMR spectroscopy to investigate the recognition and binding of a fragment from the disordered protein Gab2 by the growth factor receptor-bound protein 2 (Grb2), a key interaction for normal cell signaling and cancer development. Structural ensemble refinement by NMR chemical shifts, thermodynamics measurements, and analysis of point mutations indicated that the population of preexisting bound conformations in the free-state ensemble of Gab2 is an essential determinant for recognition and binding by Grb2. A key role was found for transient polyproline II (PPII) structures and extended conformations. Our findings are likely to have very general implications for the biological behavior of IDPs in light of the evidence that a large fraction of these proteins possess a specific propensity to form PPII and to adopt conformations that are more extended than the typical random-coil states.

Structural Ensembles of Membrane-bound α-Synuclein Reveal the Molecular Determinants of Synaptic Vesicle Affinity

A detailed characterisation of the molecular determinants of membrane binding by α-synuclein (αS), a 140-residue protein whose aggregation is associated with Parkinson’s disease, is of fundamental significance to clarify the manner in which the balance between functional and dysfunctional processes are regulated for this protein. Despite its biological relevance, the structural nature of the membrane-bound state αS remains elusive, in part because of the intrinsically dynamic nature of the protein and also because of the difficulties in studying this state in a physiologically relevant environment. In the present study we have used solid-state NMR and restrained MD simulations to refine structure and topology of the N-terminal region of αS bound to the surface of synaptic-like membranes. This region has fundamental importance in the binding mechanism of αS as it acts as to anchor the protein to lipid bilayers. The results enabled the identification of the key elements for the biological properties of αS in its membrane-bound state.

Inhibition of α-Synuclein Fibril Elongation by Hsp70 Is Governed by a Kinetic Binding Competition between α-Synuclein Species

The Hsp70 family of chaperones plays an essential role in suppressing protein aggregation in the cell. Here we investigate the factors controlling the intrinsic ability of human Hsp70 to inhibit the elongation of amyloid fibrils formed by the Parkinsons disease-related protein α-synuclein. Using kinetic analysis, we show that Hsp70 binds preferentially to α-synuclein fibrils as a consequence of variations in the association and dissociation rate constants of binding to the different aggregated states of the protein. Our findings illustrate the importance of the kinetics of binding of molecular chaperones, and also of potential therapeutic molecules, in the efficient suppression of specific pathogenic events linked to neurodegeneration.

1H, 13C and 15N resonance assignments of human muscle acylphosphatase

Human muscle acylphosphatase (mAcP) is an enzyme with a ferrodoxin-like topology whose primary role is to hydrolyze the carboxyl-phosphate bonds of acylphosphates. The protein has been widely used as a model system for elucidating the molecular determinants of protein folding and misfolding. We present here the full NMR assignments of the backbone and side chains resonances of mAcP complexed with phosphate, thus providing an important resource for future solution-state NMR spectroscopic studies of the structure and dynamics of this protein in the contexts of protein folding and misfolding.

C-terminal calcium binding of α-synuclein modulates synaptic vesicle interaction

Alpha-synuclein is known to bind to small unilamellar vesicles (SUVs) via its N terminus, which forms an amphipathic alpha-helix upon membrane interaction. Here we show that calcium binds to the C terminus of alpha-synuclein, therewith increasing its lipid-binding capacity. Using CEST-NMR, we reveal that alpha-synuclein interacts with isolated synaptic vesicles with two regions, the N terminus, already known from studies on SUVs, and additionally via its C terminus, which is regulated by the binding of calcium. Indeed, dSTORM on synaptosomes shows that calcium mediates the localization of alpha-synuclein at the pre-synaptic terminal, and an imbalance in calcium or alpha-synuclein can cause synaptic vesicle clustering, as seen ex vivo and in vitro. This study provides a new view on the binding of alpha-synuclein to synaptic vesicles, which might also affect our understanding of synucleinopathies.Alpha-synuclein is associated with neuronal dysfunction in Parkinson’s disease. This study shows that alpha-synuclein interacts with neuronal synaptic vesicles in a calcium-dependent fashion, and this interaction is important for synaptic vesicle clustering.

Order and disorder in the physiological membrane binding of α-synuclein

α-Synuclein (αS) is a neuronal protein that localises predominantly at the presynaptic terminals, and whose fibrillar aggregates are the major constituents of Lewy bodies in Parkinsons disease. In vivo αS is partitioned between water-soluble and membrane-bound states, and this highly regulated equilibrium influences its biological behaviour under both physiological and pathological conditions. Here we discuss the sequence and structural determinants underlying the transition between the unstructured cytosolic and partially structured membrane-bound states of αS. The balance between order and disorder in this protein system is crucial for the overall regulation of the membrane affinity, the ability to induce the clustering of synaptic vesicles, and the tendency to self assemble into amyloid fibrils at the surface of biological membranes.

Calcium binding at the C-terminus of α-synuclein modulates synaptic vesicle interaction

J.L. was supported by a research fellowship from the Deutsche Forschungsgemeinschaft (DFG; award LA 3609/2-1). M.Z. acknowledges funding from the Eugenides Foundation. C.F.K. acknowledges funding from the UK Engineering and Physical Sciences Research Council (EPSRC). A.DS. acknowledges funding from the UK Medical Research Council (MRC, MR/N000676/1). A.DS. and G.F. acknowledge funding from Parkinsons UK (G-1508). G.S.K. and C.F.K. acknowledge funding from the Wellcome Trust, the UK Medical Research Council (MRC), Alzheimer Research UK (ARUK), and Infinitus China Ltd. J.L. and A.D.S. acknowledge Alzheimer Research UK (ARUK) travel grants.

Molecular determinants of the interaction of EGCG with ordered and disordered proteins

The aggregation process of peptides and proteins is of great relevance as it is associated with a wide range of highly debilitating disorders, including Alzheimers and Parkinsons diseases. The natural product (‐)‐epigallocatechin‐3‐gallate (EGCG) can redirect this process away from amyloid fibrils and towards non‐toxic oligomers. In this study we used nuclear magnetic resonance (NMR) spectroscopy to characterize the binding of EGCG to a set of natively structured and unstructured proteins. The results show that the binding process is dramatically dependent on the conformational properties of the protein involved, as EGCG interacts with different binding modes depending on the folding state of the protein. We used replica exchange molecular dynamics simulations to reproduce the trends observed in the NMR experiments, and analyzed the resulting samplings to identify the dominant direct interactions between EGCG and ordered and disordered proteins.