Biology subjects

Bradley, J. M.

Publications and source records attributed to Bradley, J. M..

3 recordsLinked to original sources

bioRxiv2025

Human mitochondrial ferritin exhibits highly unusual iron-O2 chemistry distinct from that of cytosolic ferritins

Ferritins are ubiquitous proteins that function in iron storage and detoxification. Mammalian tissues that are metabolically highly active contain, in addition to the ubiquitous cytosolic ferritin, a ferritin that is localised to mitochondria. Mitochondrial ferritin (FtMt) functions to protect against oxidative stress and is found at higher levels in disease states that are associated with abnormal iron accumulation, such as Alzheimers and Parkinsons. Here we demonstrate that, despite 80% sequence identity with cytosolic human H-chain ferritin, Fe2+ oxidation at the catalytic diiron ferroxidase centre of FtMt proceeds via a distinct mechanism involving radical formation on a strictly conserved Tyr residue (Tyr34), and a mixed-valent ferroxidase centre (MVFC) that is readily detected under the O2-limiting conditions typical of mitochondria. Tyr34 is key for the activation of O2 and stability of the MVFC. The highly unusual iron-O2 chemistry exhibited by FtMt demonstrates that high levels of sequence identity between enzymes does not guarantee similarity of catalytic mechanism; here we explore the possible origin of the mechanistic differences between FtMt and cytosolic human H-chain ferritin.

biochemistry↗

bioRxiv2024

Iron and redox sensing in plants: properties of the hemerythrin-like domains of Arabidopsis BRUTUS and BRUTUS-LIKE2 proteins

Iron uptake in plants is negatively regulated by highly conserved hemerythrin (Hr) E3 ubiquitin ligases exemplified by Arabidopsis thaliana BRUTUS (BTS). Physiological studies suggest these are the elusive plant iron sensors, but biochemical evidence is lacking. Here we demonstrate that the N-terminal domains of BTS and BTS-LIKE2 (BTSL2) respectively bind three and two diiron centres within three closely packed Hr-like subdomains. The centres can be reversibly oxidized by O2 and H2O2, resulting in a di-Fe3+ form that is non-labile. In the reduced state, a proportion of the iron becomes labile, based on accessibility to Fe2+ chelators and reconstitution experiments, consistent with dynamic iron binding. Impaired iron binding and altered redox properties in the BTS dgl variant correlate with diminished capacity to suppress the downstream signalling cascade. These data provide the biochemical foundation for a mechanistic model of how BTS/Ls function as iron sensors that are unique to the plant kingdom.

biochemistry↗

bioRxiv2022

Identification of candidate virulence loci in Striga hermonthica, a devastating parasite of African cereal crops

O_LIParasites have evolved proteins, Virulence Factors (VFs), that facilitate plant colonization, yet VFs mediating parasitic plant-host interactions are poorly understood. Striga hermonthica is an obligate, root-parasitic plant of cereal hosts in sub-Saharan Africa, causing devastating yield losses. Understanding the molecular nature and allelic variation of VFs in S. hermonthica is essential for breeding resistance and delaying the evolution of parasite virulence. C_LIO_LIWe assembled the S. hermonthica genome and identified secreted proteins by in silico prediction. Pooled sequencing of parasites growing on a susceptible and a strongly resistant rice host allowed us to scan for loci where selection imposed by the resistant host had elevated the frequency of alleles contributing to successful colonisation. C_LIO_LIThirty-eight putatively secreted VFs had extremely different allele frequencies with functions including host cell wall modification, protease inhibitors, oxidoreductase and kinase activities. These candidate loci had significantly higher Tajimas D than the genomic background, consistent with balancing selection. C_LIO_LIOur results reveal diverse strategies used by S. hermonthica to overcome different layers of host resistance. Understanding the maintenance of variation at virulence loci by balancing selection will be critical to managing the evolution of virulence as a part of a sustainable control strategy. C_LI

plant biology↗