Biology subjects

Frieg, B.

Publications and source records attributed to Frieg, B..

4 recordsLinked to original sources

bioRxiv2022

The 3D structure of lipidic fibrils of α-synuclein

-synuclein (Syn) is abundant in neurons, but its misfolding and abnormal fibrillization are associated with severe neurodegenerative diseases. Although interactions between Syn and phospholipid membranes are relevant during Syn fibril assembly, insights into the interactions of Syn fibrils with phospholipids have remained elusive. Here, we present six novel polymorphic atomic structures of Syn fibrils aggregated in the presence of phospholipids. The structures reveal that phospholipids favor a novel protofilament fold, mediate an unusual arrangement of protofilaments, and fill the central cavities between the protofilaments. These findings provide a structural rationale for fibril-induced lipid extraction, a mechanism likely to be involved in the development of -synucleinopathies.

molecular biology↗

bioRxiv2021

Biophysical and pharmacokinetic characterization of a small-molecule inhibitor of RUNX1/ETO tetramerization with anti-leukemic effects

Acute myeloid leukemia (AML) is a malignant disease of immature myeloid cells and the most prevalent acute leukemia among adults. The oncogenic homo-tetrameric fusion protein RUNX1/ETO results from the chromosomal translocation t(8;21) and is found in AML patients. The nervy homology region 2 (NHR2) domain of ETO mediates tetramerization; this oligomerization is essential for oncogenic activity. Previously, we identified the first-in-class small-molecule inhibitor of NHR2 tetramer formation, 7.44, which was shown to specifically interfere with NHR2, restore gene expression down-regulated by RUNX1/ETO, inhibit the proliferation of RUNX1/ETO-depending SKNO-1 cells, and reduce the RUNX1/ETO-related tumor growth in a mouse model. However, no biophysical and structural characterization of 7.44 binding to the NHR2 domain has been reported. Likewise, the compound has not been characterized as to physicochemical, pharmacokinetic, and toxicological properties. Here, we characterize the interaction between the NHR2 domain of RUNX1/ETO and 7.44 by biophysical assays and show that 7.44 interferes with NHR2 tetramer stability and leads to an increase in the dimer population of NHR2. The affinity of 7.44 with respect to binding to NHR2 is Klig = 3.95 {+/-} 1.28 M. By NMR spectroscopy combined with molecular dynamics simulations, we show that 7.44 binds with both heteroaromatic moieties to NHR2 and interacts with or leads to conformational changes in the N-termini of the NHR2 tetramer. Finally, we demonstrate that 7.44 has favorable physicochemical, pharmacokinetic, and toxicological properties. Together with biochemical, cellular, and in vivo assessments, the results reveal 7.44 as a lead for further optimization towards targeted therapy of t(8;21) AML.

biophysics↗

bioRxiv2021

α-Synuclein polymorphism determines oligodendroglial dysfunction

Synucleinopathies, such as Parkinsons disease (PD) and Multiple System Atrophy (MSA) are progressive and unremitting neurological diseases. For both PD and MSA, -synuclein fibril inclusions inside brain cells are neuropathological hallmarks. In addition, amplification of -synuclein fibrils from body fluids is a potential biomarker distinguishing PD from MSA. However, little is known about the structure of -synuclein fibrils amplified from human samples and its connection to -synuclein fibril structure in the human brain. Here we amplified -synuclein fibrils from PD and MSA brain tissue, characterized its seeding potential in oligodendroglia, and determined the 3D structures by cryo-electron microscopy. We show that the -synuclein fibrils from a MSA patient are more potent in recruiting the endogenous -synuclein and evoking a redistribution of TPPP/p25 protein in mouse primary oligoden-droglial cultures compared to those amplified from a PD patient. Cryo-electron microscopy shows that the PD- and MSA-amplified -synuclein fibrils share a similar protofilament fold but differ in their inter-protofilament interface. The structures of the brain-tissue amplified -synuclein fibrils are also similar to other in vitro and ex vivo -synuclein fibrils. Together with published data, our results suggest that Syn fibrils differ between PD and MSA in their quaternary arrangement and could further vary between different forms of PD and MSA.

neuroscience↗

bioRxiv2020

Functional and structural characterization of interactions between opposite subunits in HCN pacemaker channels

Hyperpolarization-activated and cyclic nucleotide (HCN) modulated channels are tetrameric cation channels. In each of the four subunits, the intracellular cyclic nucleotide-binding domain (CNBD) is coupled to the transmembrane domain via a helical structure, the C-linker. High-resolution channel structures suggest that the C-linker enables functionally relevant interactions with the opposite subunit, which might be critical for coupling the conformational changes in the CNBD to the channel pore. We combined mutagenesis, patch-clamp technique, confocal patch-clamp fluorometry, and molecular dynamics simulations to show that residue K464 of the C-linker is essential for stabilizing the closed state of the mHCN2 channel by forming interactions with the opposite subunit. MD simulations revealed that both cAMP and K464E induce a rotation of the intracellular domain relative to the channel pore, weakening the autoinhibitory effect of the unoccupied CL-CNBD region. The adopted poses are in excellent agreement with structural results.

biophysics↗