PhD in Biophysics (Stockholm University).
Researcher in Biomolecular Mass Spectrometry (Department of Materials and Environmental Chemistry, Stockholm University, and Department of Microbiology Tumor and Cell Biology, Karolinska Insititute). Wenner-Gren Fellow.
PhD Thesis ("Capturing transient peptide assemblies associated with Alzheimer's Disease")
See below for a summary of my research.
Native mass spectrometry
I employ mass spectrometry to study intact folded proteins and their native complexes, including non-covalently bound ligands and other interaction partners. So-called native MS accomplishes this, without any need for covalent crosslinking or labeling, by gentle sample and instrument conditions that retains non-covalent interactions and overall tertial/quaternary structure within proteins/protein complexes inside the mass spectrometer. MS is further coupled to ion mobility spectrometry, which reports on the gas phase structure of such intact assemblies.
Native MS is perfomed together with Leopold Ilag (SU) and Michael Landreh (KI/UU).
Protein aggregation and intermediate oligomeric species
Research suggests that it is the soluble Amyloid-β (Aβ) peptide oligomers and not the mature amyloid fibrils that are the main neurotoxic species in Alzheimer's disease. These peptide assemblies are formed in the early stages of aggregation, and the exact structures and oligomer distribution are not well known. I study the assembly of Aβ oligomers and how this is affected by both intrinsic and extrinsic factors, using experimental biophysical techniques as well as computational modeling. The amyloid work is done together with Astrid Gräslund (SU) and Birgit Strodel (Forschungszentrum Jülich).
I am especially interested in the effect of membrane-environments and anti-amyloid chaperones on the oligomer formation process. The amyloid oligomer-binding chaperone DNAJB6 is studied together with Cecilia Emanuelsson and Sara Linse (LU).
Recent work together with Cagla Sahin (KI/Copenhagen University), also involve the role of liquid-liquid phase separation (LLPS) and condensate formation in protein aggregation processes.
Gas phase protein structure and infrared multiple-photon dissociation spectroscopy
I am very interested in how protein structures are affected by the transfer from aqueous solution to the gas phase of the mass spectrometer. I therefore plan to use infrared multiple-photon dissociation (IRMPD) spectroscopy to study the secondary structure of protein ions inside the mass spectrometer. Such measurments could also be used to for example follow the onset of β-sheet formation in growing protein aggregates. This is done together with Kevin Pagel (Freie Universität Berlin).
Bibliometric summary (2023):
21 papers, 405 citations, h-index of 9.
I urval från Stockholms universitets publikationsdatabas
Native Ion Mobility-Mass Spectrometry Reveals the Formation of beta-Barrel Shaped Amyloid-beta Hexamers in a Membrane-Mimicking Environment
2019. Nicklas Österlund (et al.). Journal of the American Chemical Society 141 (26), 10440-10450Artikel
The mechanisms behind the Amyloid-beta (A beta) peptide neurotoxicity in Alzheimer's disease are intensely studied and under debate. One suggested mechanism is that the peptides assemble in biological membranes to form beta-barrel shaped oligomeric pores that induce cell leakage. Direct detection of such putative assemblies and their exact oligomeric states is however complicated by a high level of heterogeneity. The theory consequently remains controversial, and the actual formation of pore structures is disputed. We herein overcome the heterogeneity problem by employing a native mass spectrometry approach and demonstrate that A beta(1-42) peptides form coclusters with membrane mimetic detergent micelles. The coclusters are gently ionized using nanoelectrospray and transferred into the mass spectrometer where the detergent molecules are stripped away using collisional activation. We show that A beta(1-42) indeed oligomerizes over time in the micellar environment, forming hexamers with collision cross sections in agreement with a general beta-barrel structure. We also show that such oligomers are maintained and even stabilized by addition of lipids. A beta(1-40) on the other hand form significantly lower amounts of oligomers, which are also of lower oligomeric state compared to A beta(1-42) oligomers. Our results thus support the oligomeric pore hypothesis as one important cell toxicity mechanism in Alzheimer's disease. The presented native mass spectrometry approach is a promising way to study such potentially very neurotoxic species and how they could be stabilized or destabilized by molecules of cellular or therapeutic relevance.
Amyloid-β oligomers are captured by the DNAJB6 chaperone
2020. Nicklas Österlund (et al.). Journal of Biological Chemistry 295 (24), 8135-8144Artikel
A human molecular chaperone protein, DnaJ heat shock protein family (Hsp40) member B6 (DNAJB6), efficiently inhibits amyloid aggregation. This inhibition depends on a unique motif with conserved serine and threonine (S/T) residues that have a high capacity for hydrogen bonding. Global analysis of kinetics data has previously shown that DNAJB6 especially inhibits the primary nucleation pathways. These observations indicated that DNAJB6 achieves this remarkably effective and sub-stoichiometric inhibition by interacting not with the monomeric unfolded conformations of the amyloid-? symbol (A?) peptide but with aggregated species. However, these pre-nucleation oligomeric aggregates are transient and difficult to study experimentally. Here, we employed a native MS-based approach to directly detect oligomeric forms of A? formed in solution. We found that WT DNAJB6 considerably reduces the signals from the various forms of A? (1?40) oligomers, whereas a mutational DNAJB6 variant in which the S/T residues have been substituted with alanines does not. We also detected signals that appeared to represent DNAJB6 dimers and trimers to which varying amounts of A? are bound. These data provide direct experimental evidence that it is the oligomeric forms of A? that are captured by DNAJB6 in a manner which depends on the S/T residues. We conclude that, in agreement with the previously observed decrease in primary nucleation rate, strong binding of A? oligomers to DNAJB6 inhibits the formation of amyloid nuclei.
Ion mobility-mass spectrometry shows stepwise protein unfolding under alkaline conditions
2021. Cagla Sahin (et al.). Chemical Communications 57 (12), 1450-1453Artikel
Although native mass spectrometry is widely applied to monitor chemical or thermal protein denaturation, it is not clear to what extent it can inform about alkali-induced unfolding. Here, we probe the relationship between solution- and gas-phase structures of proteins under alkaline conditions. Native ion mobility-mass spectrometry reveals that globular proteins are destabilized rather than globally unfolded, which is supported by solution studies, providing detailed insights into alkali-induced unfolding events. Our results pave the way for new applications of MS to monitor structures and interactions of proteins at high pH.
Mass Spectrometry and Machine Learning Reveal Determinants of Client Recognition by Antiamyloid Chaperones
2022. Nicklas Österlund (et al.). Molecular & Cellular Proteomics 21 (10)Artikel
The assembly of proteins and peptides into amyloid fibrils is causally linked to serious disorders such as Alzheimer’s disease. Multiple proteins have been shown to prevent amyloid formation in vitro and in vivo, ranging from highly specific chaperone–client pairs to completely nonspecific binding of aggregation-prone peptides. The underlying interactions remain elusive. Here, we turn to the machine learning–based structure prediction algorithm AlphaFold2 to obtain models for the nonspecific interactions of β-lactoglobulin, transthyretin, or thioredoxin 80 with the model amyloid peptide amyloid β and the highly specific complex between the BRICHOS chaperone domain of C-terminal region of lung surfactant protein C and its polyvaline target. Using a combination of native mass spectrometry (MS) and ion mobility MS, we show that nonspecific chaperoning is driven predominantly by hydrophobic interactions of amyloid β with hydrophobic surfaces in β-lactoglobulin, transthyretin, and thioredoxin 80, and in part regulated by oligomer stability. For C-terminal region of lung surfactant protein C, native MS and hydrogen–deuterium exchange MS reveal that a disordered region recognizes the polyvaline target by forming a complementary β-strand. Hence, we show that AlphaFold2 and MS can yield atomistic models of hard-to-capture protein interactions that reveal different chaperoning mechanisms based on separate ligand properties and may provide possible clues for specific therapeutic intervention.
Structural Basis for Dityrosine-Mediated Inhibition of α-Synuclein Fibrillization
2022. Cagla Sahin (et al.). Journal of the American Chemical Society 144 (27), 11949-11954Artikel
α-Synuclein (α-Syn) is an intrinsically disordered protein which self-assembles into highly organized β-sheet structures that accumulate in plaques in brains of Parkinson’s disease patients. Oxidative stress influences α-Syn structure and self-assembly; however, the basis for this remains unclear. Here we characterize the chemical and physical effects of mild oxidation on monomeric α-Syn and its aggregation. Using a combination of biophysical methods, small-angle X-ray scattering, and native ion mobility mass spectrometry, we find that oxidation leads to formation of intramolecular dityrosine cross-linkages and a compaction of the α-Syn monomer by a factor of √2. Oxidation-induced compaction is shown to inhibit ordered self-assembly and amyloid formation by steric hindrance, suggesting an important role of mild oxidation in preventing amyloid formation.
Membrane-mimetic systems for biophysical studies of the amyloid-beta peptide
2019. Nicklas Österlund (et al.). Biochimica et Biophysica Acta - Proteins and Proteomics 1867 (5), 492-501Artikel
The interplay between the amyloid-beta (A beta) peptide and cellular membranes have been proposed as an important mechanism for toxicity in Alzheimer's disease (AD). Membrane environments appear to influence A beta aggregation and may stabilize intermediate A beta oligomeric states that are considered to be neurotoxic. One important role for molecular biophysics within the field of A beta studies is to characterize the structure and dynamics of the A beta peptide in various states, as well as the kinetics of transfer between these states. Because biological cell membranes are very complex, simplified membrane models are needed to facilitate studies of A beta and other amyloid proteins in lipid environments. In this review, we examine different membrane-mimetic systems available for molecular studies of A beta. An introduction to each system is given, and examples of important findings are presented for each system. The benefits and drawbacks of each system are discussed from methodical and biological perspectives.
Amyloid-beta Peptide Interactions with Amphiphilic Surfactants
2018. Nicklas Österlund (et al.). ACS Chemical Neuroscience 9 (7), 1680-1692Artikel
The amphiphilic nature of the amyloid-beta (A beta) peptide associated with Alzheimer's disease facilitates various interactions with biomolecules such as lipids and proteins, with effects on both structure and toxicity of the peptide. Here, we investigate these peptide-amphiphile interactions by experimental and computational studies of A beta(1-40) in the presence of surfactants with varying physicochemical properties. Our findings indicate that electrostatic peptide-surfactant interactions are required for coclustering and structure induction in the peptide and that the strength of the interaction depends on the surfactant net charge. Both aggregation-prone peptide-rich coclusters and stable surfactant-rich coclusters can form. Only A beta(1-40) monomers, but not oligomers, are inserted into surfactant micelles in this surfactant-rich state. Surfactant headgroup charge is suggested to be important as electrostatic peptide-surfactant interactions on the micellar surface seems to be an initiating step toward insertion. Thus, no peptide insertion or change in peptide secondary structure is observed using a nonionic surfactant. The hydrophobic peptide-surfactant interactions instead stabilize the A beta monomer, possibly by preventing self-interaction between the peptide core and C terminus, thereby effectively inhibiting the peptide aggregation process. These findings give increased understanding regarding the molecular driving forces for A beta aggregation and the peptide interaction with amphiphilic biomolecules.
Role of hydrophobic residues for the gaseous formation of helical motifs
2019. Lin Liu (et al.). Chemical Communications 55 (35), 5147-5150Artikel
The secondary structure content of proteins and their complexes may change significantly on passing from aqueous solution to the gas phase (as in mass spectrometry experiments). In this work, we investigate the impact of hydrophobic residues on the formation of the secondary structure of a real protein complex in the gas phase. We focus on a well-studied protein complex, the amyloid- (1-40) dimer (2A). Molecular dynamics simulations reproduce the results of ion mobility-mass spectrometry experiments. In addition, a helix (not present in the solution) is identified involving (19)FFAED(23), consistent with infrared spectroscopy data on an A segment. Our simulations further point to the role of hydrophobic residues in the formation of helical motifs - hydrophobic sidechains shield helices from being approached by residues that carry hydrogen bond sites. In particular, two hydrophobic phenylalanine residues, F19 and F20, play an important role for the helix, which is induced in the gas phase in spite of the presence of two carboxyl-containing residues.