Protein 3D structure determination by high-resolution solid-state NMR

The clinical drug candidate anle138b binds in a cavity of lipidic α-synuclein fibrils

Aggregation of amyloidogenic proteins is a characteristic of multiple neurodegenerative diseases. Atomic resolution of small molecule binding to such pathological protein aggregates is of interest for the development of therapeutics and diagnostics. Here we investigate the interaction between α-synuclein fibrils and anle138b, a clinical drug candidate for disease modifying therapy in neurodegeneration and a promising scaffold for positron emission tomography tracer design. We used nuclear magnetic resonance spectroscopy and the cryogenic electron microscopy structure of α-synuclein fibrils grown in the presence of lipids to locate anle138b within a cavity formed between two β-strands. We explored and quantified multiple binding modes of the compound in detail using molecular dynamics simulations. Our results reveal stable polar interactions between anle138b and backbone moieties inside the tubular cavity of the fibrils. Such cavities are common in other fibril structures as well.

VirtualSpectrum, a tool for simulating peak list for multi-dimensional NMR spectra

NMR spectroscopy is a widely used technique for characterizing the structure and dynamics of macromolecules. Often large amounts of NMR data are required to characterize the structure of proteins. To save valuable time and resources on data acquisition, simulated data is useful in the developmental phase, for data analysis, and for comparison with experimental data. However, existing tools for this purpose can be difficult to use, are sometimes specialized for certain types of molecules or spectra, or produce too idealized data. Here we present a fast, flexible and robust tool, VirtualSpectrum, for generating peak lists for most multi-dimensional NMR experiments for both liquid and solid state NMR. It is possible to tune the quality of the generated peak lists to include sources of artifacts from peak overlap, noise and missing signals. VirtualSpectrum uses an analytic expression to represent the spectrum and derive the peak positions, seamlessly handling overlap between signals. We demonstrate our tool by comparing simulated and experimental spectra for different multi-dimensional NMR spectra and analyzing systematically three cases where overlap between peaks is particularly relevant; solid state NMR data, liquid state NMR homonuclear (1)H and (15)N-edited spectra, and 2D/3D heteronuclear correlation spectra of unstructured proteins. We analyze the impact of protein size and secondary structure on peak overlap and on the accuracy of structure determination based on data of different qualities simulated by VirtualSpectrum.

[Structural study on small molecules in biological solid samples by using solid state NMR]

Many small molecule drugs have molecular targets that are non-crystalline and insoluble biological matrices, such as proteins embedded in lipid membrane, cell membranes, and cell walls. To understand the action mechanisms, it is essential to determine the binding structure with atomic-level resolution. Although solution nuclear magnetic resonance (NMR) and X-ray crystallography have been used to determine molecular structures of cell membrane and membrane proteins, these methods are unable to reproduce the complexity of biological systems because either solubilization or crystallization of target molecules is requisite. For structural studies of insoluble non-crystalline biological samples, so-called "biological solids", high resolution distance measurements using solid-state NMR are indispensable techniques, of which rotational-echo double-resonance (REDOR) is one of the most widely used methods. In this paper, a brief introduction to REDOR NMR and its applications to structural studies on the antifungal amphotericin B-membrane phospholipid complex and a structural elucidation of photorespiration metabolites in plant cells without extraction or isolation is provided.

ARIA for solution and solid-state NMR

In solution or solid-state, determining the three-dimensional structure of biomolecules by Nuclear -Magnetic Resonance (NMR) normally requires the collection of distance information. The interpretation of the spectra containing this distance information is a critical step in an NMR structure determination. In this chapter, we present the Ambiguous Restraints for Iterative Assignment (ARIA) program for automated cross-peak assignment and determination of macromolecular structure from solution and solid-state NMR experiments. While the program was initially designed for the assignment of nuclear Overhauser effect (NOE) resonances, it has been extended to the interpretation of magic-angle spinning (MAS) solid-state NMR data. This chapter first details the concepts and procedures carried out by the program. Then, we describe both the general strategy for structure determination with ARIA 2.3 and practical aspects of the technique. ARIA 2.3 includes all recent developments. such as an extended integration of the Collaborative Computing Project for the NMR community (CCPN), the incorporation of the log-harmonic distance restraint potential and an automated treatment of symmetric oligomers.

Advances in automated NMR protein structure determination

Around half of all protein structures solved nowadays using solution-state nuclear magnetic resonance (NMR) spectroscopy have been because of automated data analysis. The pervasiveness of computational approaches in general hides, however, a more nuanced view in which the full variety and richness of the field appears. This review is structured around a comparison of methods associated with three NMR observables: classical nuclear Overhauser effect (NOE) constraint gathering in contrast with more recent chemical shift and residual dipole coupling (RDC) based protocols. In each case, the emphasis is placed on the latest research, covering mainly the past 5 years. By describing both general concepts and representative programs, the objective is to map out a field in which--through the very profusion of approaches--it is all too easy to lose one's bearings.