Solid-state nuclear magnetic resonance (ssNMR) spectroscopy enables the structural characterization of a diverse array of biological assemblies that include amyloid fibrils, non-amyloid aggregates, membrane-associated proteins and viral capsids. Such biological samples feature functionally relevant molecular dynamics, which often affect different parts of the sample in different ways. Solid-state NMR experiments' sensitivity to dynamics represents a double-edged sword. On the one hand, it offers a chance to measure dynamics in great detail. On the other hand, certain types of motion lead to signal loss and experimental inefficiencies that at first glance interfere with the application of ssNMR to overly dynamic proteins. Dynamics-based spectral editing (DYSE) ssNMR methods leverage motion-dependent signal losses to simplify spectra and enable the study of sub-structures with particular motional properties.

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The Hsp40/Hsp70 chaperone families combine versatile folding capacity with high substrate specificity, which is mainly facilitated by Hsp40s. The structure and function of many Hsp40s remain poorly understood, particularly oligomeric Hsp40s that suppress protein aggregation. Here, we used a combination of biochemical and structural approaches to shed light on the domain interactions of the Hsp40 DnaJB8, and how they may influence recruitment of partner Hsp70s. We identify an interaction between the J-Domain (JD) and C-terminal domain (CTD) of DnaJB8 that sequesters the JD surface, preventing Hsp70 interaction. We propose a model for DnaJB8-Hsp70 recruitment, whereby the JD-CTD interaction of DnaJB8 acts as a reversible switch that can control the binding of Hsp70. These findings suggest that the evolutionarily conserved CTD of DnaJB8 is a regulatory element of chaperone activity in the proteostasis network.

Huntington’s disease, like other neurodegenerative diseases, continues to lack an effective cure. Current treatments that address early symptoms ultimately fail Huntington’s disease patients and their families, with the disease typically being fatal within 10–15 years from onset. Huntington’s disease is an inherited disorder with motor and mental impairment, and is associated with the genetic expansion of a CAG codon repeat encoding a polyglutamine-segment-containing protein called huntingtin. These Huntington’s disease mutations cause misfolding and aggregation of fragments of the mutant huntingtin protein, thereby likely contributing to disease toxicity through a combination of gain-of-toxic-function for the misfolded aggregates and a loss of function from sequestration of huntingtin and other proteins. As with other amyloid diseases, the mutant protein forms non-native fibrillar structures, which in Huntington’s disease are found within patients’ neurons. The intracellular deposits are associated with dysregulation of vital processes, and inter-neuronal transport of aggregates may contribute to disease progression. However, a molecular understanding of these aggregates and their detrimental effects has been frustrated by insufficient structural data on the misfolded protein state. In this review, we examine recent developments in the structural biology of polyglutamine-expanded huntingtin fragments, and especially the contributions enabled by advances in solid-state nuclear magnetic resonance spectroscopy. We summarize and discuss our current structural understanding of the huntingtin deposits and how this information furthers our understanding of the misfolding mechanism and disease toxicity mechanisms. Impact statement Many incurable neurodegenerative disorders are associated with, and potentially caused by, the amyloidogenic misfolding and aggregation of proteins. Usually, complex genetic and behavioral factors dictate disease risk and age of onset. Due to its principally mono-genic origin, which strongly predicts the age-of-onset by the extent of CAG repeat expansion, Huntington’s disease (HD) presents a unique opportunity to dissect the underlying disease-causing processes in molecular detail. Yet, until recently, the mutant huntingtin protein with its expanded polyglutamine domain has resisted structural study at the atomic level. We present here a review of recent developments in HD structural biology, facilitated by breakthrough data from solid-state NMR spectroscopy, electron microscopy, and complementary methods. The misfolded structures of the fibrillar proteins inform our mechanistic understanding of the disease-causing molecular processes in HD, other CAG repeat expansion disorders, and, more generally, protein deposition disease.

Noncollagenous proteins regulate the formation of the mineral constituent in hard tissue. The mineral formed contains apatite crystals coated by a functional disordered calcium phosphate phase. Although the crystalline phase of bone mineral was extensively investigated, little is known about the disordered layer's composition and structure, and less is known regarding the function of noncollagenous proteins in the context of this layer. In the current study, apatite was prepared with an acidic peptide (ON29) derived from the bone/dentin protein osteonectin. The mineral formed comprises needle-shaped hydroxyapatite crystals like in dentin and a stable disordered phase coating the apatitic crystals as shown using X-ray diffraction, transmission electron microscopy, and solid-state NMR techniques. The peptide, embedded between the mineral particles, reduces the overall phosphate content in the mineral formed as inferred from inductively coupled plasma and elemental analysis results. Magnetization transfers between disordered phase species and apatitic phase species are observed for the first time using 2D (1)H-(31)P heteronuclear correlation NMR measurements. The dynamics of phosphate magnetization transfers reveal that ON29 decreases significantly the amount of water molecules in the disordered phase and increases slightly their content at the ordered-disordered interface. The peptide decreases hydroxyl to disordered phosphate transfers within the surface layer but does not influence transfer within the bulk crystalline mineral. Overall, these results indicate that control of crystallite morphology and properties of the inorganic component in hard tissue by biomolecules is more involved than just direct interaction between protein functional groups and mineral crystal faces. Subtler mechanisms such as modulation of the disordered phase composition and structural changes at the ordered-disordered interface may be involved.

Aluminum doped mixed metal oxides are popular positive electrode materials for Li-ion batteries. They are used extensively in many applications, yet their operation and limitations are not entirely understood. This work shows the advantage of using solid-state 7Li and 27Al NMR for monitoring the electrochemical properties of the doped nickel–cobalt oxide cathode material, LiNi0.8Co0.15Al0.05O2 (NCA), particularly during the first few charge/discharge cycles. The changes in the state of the material as lithium ions are intercalated and deintercalated during discharge and charge, respectively, are highlighted via the Li nuclei as a dynamic reporter and the Al nuclei as a static, material-embedded reporter. In particular, the NMR view of the cyclic change of Ni ions between paramagnetic and diamagnetic oxidation states is enhanced by monitoring both nuclei. Two protocols of cycling the NCA electrode are compared: one employing a smaller voltage window, cycled against graphite as anode, and one using a wider voltage window, cycled against a lithium metal anode. The NMR analysis unveils notable differences in the reversibility of the changes in the Ni oxidation states as charge carriers are shuttled in and out of the cathode material. The 27Al NMR data of the pristine material shows the existence of at least two distinct configurations of Ni ions around the Al dopant ions, suggesting coexistence of two disparate phases, which remain intact upon cycling. The protocol employing slower cycling versus Li anode delivers better cathode performance in the sense that more extensive relithiation occurs, and here, it is shown that the return of the local environments to their pristine electronic configurations is more complete. The 27Al and 7Li NMR results are integrated into a simple scheme exemplifying how better understanding of the local electronic changes in paramagnetic electrode materials can be captured in simple progressive plots.

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A pathological hallmark of Huntington’s disease (HD) is the formation of neuronal protein deposits containing mutant huntingtin fragments with expanded polyglutamine (polyQ) domains. Prior studies have shown the strengths of solid-state NMR (ssNMR) to probe the atomic structure of such aggregates, but have required in vitro isotopic labeling. Herein, we present an approach for the structural fingerprinting of fibrils through ssNMR at natural isotopic abundance (NA). These methods will enable the spectroscopic fingerprinting of unlabeled (e.g., ex vivo) protein aggregates and the extraction of valuable new long-range 13C–13C distance constraints.