Characterization of tau binding by gosuranemab.

Deposition of tau aggregates in the brain is a pathological hallmark of several neurodegenerative diseases, termed tauopathies, such as Alzheimer's disease (AD), corticobasal degeneration, and progressive supranuclear palsy (PSP). As transcellular spread of pathological tau aggregates has been implicated in disease progression, immunotherapy is being considered as a treatment for tauopathies. Here we report a detailed biochemical and biophysical characterization of the tau-binding properties of gosuranemab, a humanized monoclonal antibody directed against N-terminal tau that is currently being investigated as a treatment for AD. Binding experiments showed that gosuranemab exhibited high affinity for tau monomer, tau fibrils, and insoluble tau from different tauopathies. Epitope mapping studies conducted using X-ray crystallography and mutagenesis showed that gosuranemab bound to human tau residues 15-22. Immunodepletion of pathological human brain homogenates and transgenic mouse interstitial fluid (ISF) with gosuranemab resulted in reduced tau aggregation in tau biosensor cells. Preincubation of seed-competent AD-tau with gosuranemab significantly inhibited tau aggregation in mouse primary cortical neurons. Gosuranemab also significantly reduced unbound N-terminal tau in cerebrospinal fluid (CSF) from individuals with PSP and AD, and in ISF and CSF of treated transgenic mice. These results are consistent with the >90% target engagement observed in the CSF of some clinical trial dosing cohorts and support the evaluation of gosuranemab as a potential treatment for AD.

Molecular details of the yeast frataxin-Isu1 interaction during mitochondrial Fe-S cluster assembly.

Frataxin, a conserved nuclear-encoded mitochondrial protein, plays a direct role in iron-sulfur cluster biosynthesis within the ISC assembly pathway. Humans with frataxin deficiency have Friedreich's ataxia, a neurodegenerative disorder characterized by mitochondrial iron overload and disruption in Fe-S cluster synthesis. Biochemical and genetic studies have shown frataxin interacts with the iron-sulfur cluster assembly scaffold protein (in yeast, there are two, Isu1 and Isu2), indicating frataxin plays a direct role in cluster assembly, possibly by serving as an iron chaperone in the assembly pathway. Here we provide molecular details of how yeast frataxin (Yfh1) interacts with Isu1 as a structural module to improve our understanding of the multiprotein complex assembly that completes Fe-S cluster assembly; this complex also includes the cysteine desulfurase (Nfs1 in yeast) and the accessory protein (Isd11), together in the mitochondria. Thermodynamic binding parameters for protein partner and iron binding were measured for the yeast orthologs using isothermal titration calorimetry. Nuclear magnetic resonance spectroscopy was used to provide the molecular details to understand how Yfh1 interacts with Isu1. X-ray absorption studies were used to electronically and structurally characterize how iron is transferred to Isu1 and then incorporated into an Fe-S cluster. These results were combined with previously published data to generate a structural model for how the Fe-S cluster protein assembly complex can come together to accomplish Fe-S cluster assembly.

Effects of submicron particles on formation of micron-sized particles during long-term storage of an interferon-ß-1a solution.

We present evidence that homogeneous submicron particles can influence the growth rate of larger particles upon long-term storage in a temperature-dependent manner. Interferon-beta-1a was thermally stressed at 50°C for 6 h and characterized using nanoparticle tracking analysis (NTA), microflow digital imaging (MFI), and circular dichroism (CD) spectroscopy. This study showed selective formation of submicron particles exhibiting a perturbed protein conformation. These thermally induced submicron particles were spiked into an unstressed solution at three levels, and then monitored for micron-sized particle formation upon storage at 5°C and 25°C for 12 months. The resulting particle growth effects were temperature dependent. NTA and MFI results at 5°C showed little evidence that initial submicron particle levels impacted particle growth across the range ~0.03-25 µm. In contrast, MFI results at 25°C indicated that particle growth in the 1-10 µm size range correlated strongly with initial submicron particle levels, and particle counts in the 10-25 µm size range were highest after 12 months for the samples with highest initial submicron particle content.