The 140-residue protein ␣-synuclein (AS) is able to form amyloid fibrils and as such is the main component of protein inclusions involved in Parkinson's disease. We have investigated the structure and dynamics of full-length AS fibrils by high-resolution solid-state NMR spectroscopy. Homonuclear and heteronuclear 2D and 3D spectra of fibrils grown from uniformly 13 C͞ 15 N-labeled AS and AS reverse-labeled for two of the most abundant amino acids, K and V, were analyzed. 13 C and 15 N signals exhibited linewidths of <0.7 ppm. Sequential assignments were obtained for 48 residues in the hydrophobic core region. We identified two different types of fibrils displaying chemical-shift differences of up to 13 ppm in the 15 N dimension and up to 5 ppm for backbone and side-chain 13 C chemical shifts. EM studies suggested that molecular structure is correlated with fibril morphology. Investigation of the secondary structure revealed that most amino acids of the core region belong to ␤-strands with similar torsion angles in both conformations. Selection of regions with different mobility indicated the existence of monomers in the sample and allowed the identification of mobile segments of the protein within the fibril in the presence of monomeric protein. At least 35 C-terminal residues were mobile and lacked a defined secondary structure, whereas the N terminus was rigid starting from residue 22. Our findings agree well with the overall picture obtained with other methods and provide insight into the amyloid fibril structure and dynamics with residue-specific resolution.EM ͉ protein structure ͉ amyloid ͉ Parkinson's disease ͉ protein aggregation T he ability of a protein to form amyloid fibrils is increasingly recognized as a general property of all polypeptide sequences (1). It is a phenomenon common to numerous neurodegenerative diseases such as Alzheimer's and Parkinson's diseases and spongiform encephalopathies (2, 3). Thus, the investigation of the mechanism(s) of protein misfolding as well as the detailed structures of amyloid fibrils is of paramount interest (4, 5). Parkinson's disease is defined by the presence of intracellular inclusions in dopaminergic neurons, the so-called Lewy bodies, which contain a high content of fibrils formed from the 140-aa cytoplasmic protein ␣-synuclein (AS) (6). The question of whether the mature fibrils themselves or rather protofilaments or folding intermediates are the neurotoxic species responsible for the cell death of dopaminergic neurons is still a subject of great controversy (7-9).AS belongs to the class of natively unfolded proteins, i.e., it lacks a well-defined secondary structure (10, 11), although long-range interactions have been shown to stabilize an aggregation-autoinhibited global protein architecture (12). Three regions of the protein can be classified. (i) The amphipathic N terminus (residues 1-60) consists of imperfect 11-mer repeats, with the consensus motif KTKEGV. (ii) The predominantly hydrophobic middle, also known as non-A␤ component region (residues 61-95...

Proton MRS (1H MRS) provides noninvasive, quantitative metabolite profiles of tissue and has been shown to aid the clinical management of several brain diseases. Although most modern clinical MR scanners support MRS capabilities, routine use is largely restricted to specialized centers with good access to MR research support. Widespread adoption has been slow for several reasons, and technical challenges toward obtaining reliable good‐quality results have been identified as a contributing factor. Considerable progress has been made by the research community to address many of these challenges, and in this paper a consensus is presented on deficiencies in widely available MRS methodology and validated improvements that are currently in routine use at several clinical research institutions. In particular, the localization error for the PRESS localization sequence was found to be unacceptably high at 3 T, and use of the semi‐adiabatic localization by adiabatic selective refocusing sequence is a recommended solution. Incorporation of simulated metabolite basis sets into analysis routines is recommended for reliably capturing the full spectral detail available from short TE acquisitions. In addition, the importance of achieving a highly homogenous static magnetic field (B0) in the acquisition region is emphasized, and the limitations of current methods and hardware are discussed. Most recommendations require only software improvements, greatly enhancing the capabilities of clinical MRS on existing hardware. Implementation of these recommendations should strengthen current clinical applications and advance progress toward developing and validating new MRS biomarkers for clinical use.

Mutations of arginine 132 (R132) in the enzyme isocitrate dehydrogenase-1 (IDH1) are present in up to 86% of grade II and III gliomas and secondary glioblastoma. R132 mutations in IDH1 result in excess production of the metabolite 2-hydroxyglutarate (2HG), which could be used as a biomarker for this subset of gliomas. Here, we use optimized spectral-editing and two-dimensional (2D) correlation magnetic resonance spectroscopy (MRS) methods to unambiguously detect 2HG non-invasively in glioma patients with IDH1 mutations. By comparison, fitting of conventional 1D MR spectra can provide false-positive readouts owing to spectral overlap of 2HG and chemically similar brain metabolites, such as glutamate and glutamine. 2HG has been found also by 2D high-resolution magic angle spinning MRS performed ex vivo on a separate set of glioma biopsy samples. 2HG detection by in vivo or ex vivo MRS enabled detailed molecular characterization of a clinically important subset of human gliomas. This has implications for diagnosis as well as monitoring of treatments targeting IDH mutations.