The ABCB7-like Transporter PexA in Rhodobacter capsulatus maintains proper Distribution of Reactive Sulfur Species

ABSTRACT: The mitochondrial ATP-binding cassette (ABC) transporters ABCB7 in humans, Atm1 in yeast and ATM3 in plants are highly conserved in their overall architecture and particularly in their glutathione binding pocket located within the transmembrane spanning domains. These transporters have attracted interest in the last two decades based on their proposed role in connecting the mitochondrial iron-sulfur (Fe-S) cluster assembly with its cytosolic Fe-S cluster assembly (CIA) counterpart. So far, the specific compound that is transported across the membrane remains unknown. In this report we characterized the ABCB7-like transporter Rcc02305 in Rhodobacter capsulatus, which shares 47% amino acid sequence identity to its mitochondrial counterpart. The constructed interposon mutant strain in R. capsulatus displayed increased levels of intracellular reactive oxygen species without a simultaneous accumulation of the cellular iron concentration. The inhibition of endogenous glutathione biosynthesis resulted in an increase of total glutathione levels in the mutant strain. Bioinformatic analysis of the amino acid sequence motifs revealed an aminotransferase class-V pyridoxal-5’-phosphate (PLP) binding site overlapping with the Walker A motif within the nucleotide binding domains of the transporter. The PLP cofactor is well characterized in L-cysteine desulfurases like IscS and NFS1 for its role in the formation of a protein-bound persulfide group. In this report, we present a model proposing that this ABC-transporter in R. capsulatus in its inward facing open conformation first produces a nucleophilic persulfide, which further reacts in a substitution reaction with a trapped GS(S)nG bound to the TMD resulting to a mixed glutathione polysulfide. In the next step, the release of the persulfide from the PLP binding site enables ATP to bind to the Walker A motif and the subsequent hydrolysis of ATP triggers a translocation of the mixed disulfide to the periplasm. We rename the ABCB7-like transporter Rcc02305 in R. capsulatus to PexA for PLP binding exporter.

INSTRUMENT(S): Q Exactive

ORGANISM(S): Rhodobacter Capsulatus

SUBMITTER: Beata Siemiatkowska  

LAB HEAD: Silke Leimkühler

PROVIDER: PXD011591 | Pride | 2019-03-08

REPOSITORIES: Pride