Tritium Labeling of Neuromedin S by Conjugation with [3H]N-Succinimidyl Propionate.

The human neuropeptide neuromedin S (NMS) consists of 33 amino acids. The introduction of tritium atoms into NMS has not been described so far. This represents a gap for using [3H]NMS in radioreceptor binding assays or in tracking and monitoring their metabolic pathway. Two approaches for the incorporation of tritium into NMS were explored in this study: (1) halogenation at the His-18 residue followed by catalyzed iodine-127/tritium exchange and (2) conjugation of tritiated N-succinimidyl-[2,3-3H3]propionate ([3H]NSP) to at least one of the three available primary amines of amino acids Ile-1, Lys-15, and Lys-16 in the peptide sequence. Although iodination of histidine was achieved, subsequent iodine-127/deuterium exchange was unsuccessful. Derivatization at the three possible amino positions in the peptide using nonradioactive NSP resulted in a mixture of unconjugated NSM and 1- to 3-conjugations at different amino acids in the peptide sequence. Each labeling position in the mixture was assigned following detailed LC-MS/MS analysis. After separating the mixture, it was shown in an in vitro fluorometric imaging plate reader (FLIPR) and in a competitive binding assay that the propionyl-modified NMS derivatives were comparable to the unlabeled NMS, regardless of the degree of labeling and the labeling position(s). A molecular simulation with NMS in the binding pocket of the protein neuromedin U receptor 2 (NMUR2) confirmed that the possible labeling positions are located outside the binding region of NMUR2. Tritium labeling was achieved at the N-terminal Ile-1 using [3H]NSP in 7% yield with a radiochemical purity of >95% and a molar activity of 90 Ci/mmol. This approach provides access to tritiated NMS and enables new investigations to characterize NMS or corresponding NMS ligands.

Lewy pathology in Parkinson's disease consists of crowded organelles and lipid membranes.

Parkinson's disease, the most common age-related movement disorder, is a progressive neurodegenerative disease with unclear etiology. Key neuropathological hallmarks are Lewy bodies and Lewy neurites: neuronal inclusions immunopositive for the protein α-synuclein. In-depth ultrastructural analysis of Lewy pathology is crucial to understanding pathogenesis of this disease. Using correlative light and electron microscopy and tomography on postmortem human brain tissue from Parkinson's disease brain donors, we identified α-synuclein immunopositive Lewy pathology and show a crowded environment of membranes therein, including vesicular structures and dysmorphic organelles. Filaments interspersed between the membranes and organelles were identifiable in many but not all α-synuclein inclusions. Crowding of organellar components was confirmed by stimulated emission depletion (STED)-based super-resolution microscopy, and high lipid content within α-synuclein immunopositive inclusions was corroborated by confocal imaging, Fourier-transform coherent anti-Stokes Raman scattering infrared imaging and lipidomics. Applying such correlative high-resolution imaging and biophysical approaches, we discovered an aggregated protein-lipid compartmentalization not previously described in the Parkinsons' disease brain.

Structure of the malaria vaccine candidate antigen CyRPA and its complex with a parasite invasion inhibitory antibody.

Invasion of erythrocytes by Plasmodial merozoites is a composite process involving the interplay of several proteins. Among them, the Plasmodium falciparum Cysteine-Rich Protective Antigen (PfCyRPA) is a crucial component of a ternary complex, including Reticulocyte binding-like Homologous protein 5 (PfRH5) and the RH5-interacting protein (PfRipr), essential for erythrocyte invasion. Here, we present the crystal structures of PfCyRPA and its complex with the antigen-binding fragment of a parasite growth inhibitory antibody. PfCyRPA adopts a 6-bladed ß-propeller structure with similarity to the classic sialidase fold, but it has no sialidase activity and fulfills a purely non-enzymatic function. Characterization of the epitope recognized by protective antibodies may facilitate design of peptidomimetics to focus vaccine responses on protective epitopes. Both in vitro and in vivo anti-PfCyRPA and anti-PfRH5 antibodies showed more potent parasite growth inhibitory activity in combination than on their own, supporting a combined delivery of PfCyRPA and PfRH5 in vaccines.