Dataset Information

Functional and structural characterization of an ECF-type ABC transporter for vitamin B12.

ABSTRACT: Vitamin B12 (cobalamin) is the most complex B-type vitamin and is synthetized exclusively in a limited number of prokaryotes. Its biologically active variants contain rare organometallic bonds, which are used by enzymes in a variety of central metabolic pathways such as L-methionine synthesis and ribonucleotide reduction. Although its biosynthesis and role as co-factor are well understood, knowledge about uptake of cobalamin by prokaryotic auxotrophs is scarce. Here, we characterize a cobalamin-specific ECF-type ABC transporter from Lactobacillus delbrueckii, ECF-CbrT, and demonstrate that it mediates the specific, ATP-dependent uptake of cobalamin. We solved the crystal structure of ECF-CbrT in an apo conformation to 3.4 Å resolution. Comparison with the ECF transporter for folate (ECF-FolT2) from the same organism, reveals how the identical ECF module adjusts to interact with the different substrate binding proteins FolT2 and CbrT. ECF-CbrT is unrelated to the well-characterized B12 transporter BtuCDF, but their biochemical features indicate functional convergence.

SUBMITTER: Santos JA

PROVIDER: S-EPMC5997447 | biostudies-literature | 2018 May

REPOSITORIES: biostudies-literature

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Functional and structural characterization of an ECF-type ABC transporter for vitamin B12.

Santos Joana A JA Rempel Stephan S Mous Sandra Tm ST Pereira Cristiane T CT Ter Beek Josy J de Gier Jan-Willem JW Guskov Albert A Slotboom Dirk J DJ

eLife 20180529

Vitamin B12 (cobalamin) is the most complex B-type vitamin and is synthetized exclusively in a limited number of prokaryotes. Its biologically active variants contain rare organometallic bonds, which are used by enzymes in a variety of central metabolic pathways such as L-methionine synthesis and ribonucleotide reduction. Although its biosynthesis and role as co-factor are well understood, knowledge about uptake of cobalamin by prokaryotic auxotrophs is scarce. Here, we characterize a cobalamin- ...[more]

PMID: 29809140

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Project description:During evolution, chloroplasts, which originated by endosymbiosis of a prokaryotic ancestor of today's cyanobacteria with a eukaryotic host cell, were established as the site for photosynthesis. Therefore, chloroplast organelles are loaded with transition metals including iron, copper, and manganese, which are essential for photosynthetic electron transport due to their redox capacity. Although transport, storage, and cofactor-assembly of metal ions in chloroplasts are tightly controlled and crucial throughout plant growth and development, knowledge on the molecular nature of chloroplast metal-transport proteins is still fragmentary. Here, we characterized the soluble, ATP-binding ABC-transporter subunits ABCI10 and ABCI11 in Arabidopsis thaliana, which show similarities to components of prokaryotic, multisubunit ABC transporters. Both ABCI10 and ABCI11 proteins appear to be strongly attached to chloroplast-intrinsic membranes, most likely inner envelopes for ABCI10 and possibly plastoglobuli for ABCI11. Loss of ABCI10 and ABCI11 gene products in Arabidopsis leads to extremely dwarfed, albino plants showing impaired chloroplast biogenesis and deregulated metal homeostasis. Further, we identified the membrane-intrinsic protein ABCI12 as potential interaction partner for ABCI10 in the inner envelope. Our results suggest that ABCI12 inserts into the chloroplast inner envelope membrane most likely with five predicted ?-helical transmembrane domains and represents the membrane-intrinsic subunit of a prokaryotic-type, energy-coupling factor (ECF) ABC-transporter complex. In bacteria, these multisubunit ECF importers are widely distributed for the uptake of nickel and cobalt metal ions as well as for import of vitamins and several other metabolites. Therefore, we propose that ABCI10 (as the ATPase A-subunit) and ABCI12 (as the membrane-intrinsic, energy-coupling T-subunit) are part of a novel, chloroplast envelope-localized, AAT energy-coupling module of a prokaryotic-type ECF transporter, most likely involved in metal ion uptake.

Dataset Information

Functional and structural characterization of an ECF-type ABC transporter for vitamin B12.

Publications

Functional and structural characterization of an ECF-type ABC transporter for vitamin B12.

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