Biology subjects

Beckman, J. S.

Publications and source records attributed to Beckman, J. S..

4 recordsLinked to original sources

bioRxiv2025

The structure, redox chemistry and motor neuron toxicity of heterodimeric zinc-deficient SOD1-Implications for the toxic gain of function observed in ALS.

A subset of familial cases of amyotrophic lateral sclerosis (fALS) are caused by mutations to copper, zinc superoxide dismutase (Cu, Zn SOD1). There are over 200 mutations to SOD1 that have been associated with fALS and the majority of these mutations are dominantly inherited. Thus, individuals are heterozygous and express both wild-type SOD1 and the mutant form of the protein. Paradoxically, when rodent models are produced that mimic the co-expression of wild-type SOD1 with mutant fALS SOD1 the motor neuron disease accelerates. Previously, we have shown that the loss of zinc from an SOD1 kills cultured motor neurons due to a gained, redox activity catalyzed by the active-site copper. Furthermore, motor neuron toxicity of zinc-deficient SOD1 is enhanced by wild-type Cu, Zn SOD1. Because SOD1 exists as a non-covalent dimer, the enhanced toxicity might result from stabilization of the heterodimeric interface between zinc-deficient SOD1 and Cu, Zn-SOD1. However, experimentation with the heterodimer is difficult because SOD1 subunits exchange in minutes. To better characterize the role of dimer stabilization on the enhanced toxicity of fALS mutant SOD1 by wild type SOD1, we genetically tethered a zinc-deficient SOD1 subunit with a Cu, Zn SOD1 subunit with a 16-residue linker. The x-ray structure of the tethered heterodimer shows that zinc-deficient subunit adopts a wild-type-like conformation and is not misfolded. The heterodimer intermediate also produced peroxynitrite from nitric oxide, and the tethered SOD1 was strikingly toxic to primary cultures of motor neurons. This work supports the concept that zinc-deficient SOD1 is a likely toxic intermediate in ALS. Furthermore, the wild-type allele in human familial-SOD1 ALS patients may physically contribute to the dominant inheritance of SOD1 mutations through heterodimer formation.

biochemistry↗

bioRxiv2022

Microglial ferroptotic stress causes non-cell autonomous neuronal death

BackgroundFerroptosis is a form of regulated cell death characterised by lipid peroxidation as the terminal endpoint and a requirement for iron. Although it protects against cancer and infection, ferroptosis is also implicated in causing neuronal death in degenerative diseases of the central nervous system (CNS). The precise role for ferroptosis in causing neuronal death is yet to be fully resolved. MethodsTo elucidate the role of ferroptosis in neuronal death we utilised co-culture and conditioned medium transfer experiments involving microglia, astrocytes and neurones. We ratified clinical significance of our cell culture findings via assessment of human CNS tissue from cases of the fatal, paralysing neurodegenerative condition of amyotrophic lateral sclerosis (ALS). Finally, we utilised the SOD1G37R mouse model of ALS and a novel CNS-permeant ferroptosis inhibitor to verify pharmacological significance in vivo. ResultsWe found that sublethal ferroptotic stress selectively affecting microglia triggers an inflammatory cascade that results in non-cell autonomous neuronal death. Central to this cascade is the conversion of astrocytes to a neurotoxic state. We show that spinal cord tissue from cases of ALS exhibits a signature of ferroptosis that encompasses atomic, molecular and biochemical features. Moreover, a molecular correlation between ferroptosis and neurotoxic astrocytes evident in ALS-affected spinal cord is recapitulated in the SOD1G37R mouse model where treatment with the novel, CNS-permeant ferroptosis inhibitor, CuII(atsm), ameliorated these markers and was neuroprotective. ConclusionsBy showing that microglia responding to sublethal ferroptotic stress culminates in non-cell autonomous neuronal death, our results implicate microglial ferroptotic stress as a rectifiable cause of neuronal death in neurodegenerative disease. As ferroptosis is currently primarily regarded as an intrinsic cell death phenomenon, these results introduce an entirely new pathophysiological role for ferroptosis in disease.

neuroscience↗

bioRxiv2021

PermaPhosSer: autonomous synthesis of functional, permanently phosphorylated proteins

Installing stable, functional mimics of phosphorylated amino acids into proteins offers a powerful strategy to study protein regulation. Previously, a genetic code expansion (GCE) system was developed to translationally install non-hydrolyzable phosphoserine (nhpSer), with the {gamma}-oxygen replaced with carbon, but it has seen limited usage. Here, we achieve a 40-fold improvement in this system by engineering into Escherichia coli a biosynthetic pathway that produces nhpSer from the central metabolite phosphoenolpyruvate. Using this "PermaPhosSer" system - an autonomous 21-amino acid E. coli expression system for incorporating nhpSer into target proteins - we show that nhpSer faithfully mimics the effects of phosphoserine in three stringent test cases: promoting 14-3-3/client complexation, disrupting 14-3-3 dimers, and activating GSK3{beta} phosphorylation of the SARS-CoV-2 nucleocapsid protein. This facile access to nhpSer containing proteins should allow nhpSer to replace Asp and Glu as the go-to pSer phosphomimetic for proteins produced in E. coli.

synthetic biology↗

bioRxiv2020

Disrupted copper availability in sporadic ALS: Implications for CuII(atsm) as a treatment option

ObjectiveThe copper compound CuII(atsm) is in phase 2/3 testing for treatment of the neurodegenerative disease amyotrophic lateral sclerosis (ALS). CuII(atsm) consistently and reproducibly ameliorates neurodegeneration in mutant SOD1 mouse models of ALS where its neuroprotective activity has been ascribed in part to improving availability of copper to essential cuproenzymes. However, SOD1 mutations cause only ~2% of ALS cases with most cases being of unknown aetiology. Therapeutic pertinence of CuII(atsm) to sporadic ALS is therefore unclear. MethodsWe assayed post-mortem spinal cord tissue from sporadic cases of ALS for the anatomical and biochemical distribution of copper, the expression of genes involved in copper handling, and the activities of cuproenzymes. ResultsThe natural distribution of copper is disrupted in sporadic ALS. The ALS-affected tissue has a molecular signature consistent with an unsatiated requirement for copper and cuproenzyme activity is affected. Copper levels are decreased in the ventral grey matter, the primary anatomical site of neuronal loss in ALS. InterpretationMice expressing mutant SOD1 recapitulate salient features of ALS. The unsatiated requirement for copper that is evident in these mice is a biochemical target for CuII(atsm). Evidences provided here for disrupted copper bioavailability in human cases of sporadic ALS indicate that a therapeutic mechanism for CuII(atsm) involving copper bioavailability is pertinent to sporadic cases of ALS, and not just those involving mutant SOD1.

neuroscience↗