Structure and function of an Arabidopsis thaliana sulfate transporter.
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ABSTRACT:
SUBMITTER: Wang L
PROVIDER: S-EPMC8298490 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Proton/sulfate cotransporters in the plasma membranes are responsible for uptake of the environmental sulfate used in the sulfate assimilation pathway in plants. Here we report the cloning and characterization of an Arabidopsis thaliana gene, AST68, a new member of the sulfate transporter gene family in higher plants. Sequence analysis of cDNA and genomic clones of AST68 revealed that the AST68 gene is composed of 10 exons encoding a 677-aa polypeptide (74.1 kDa) that is able to functionally complement a Saccharomyces cerevisiae mutant lacking a sulfate transporter gene. Southern hybridization and restriction fragment length polymorphism mapping confirmed that AST68 is a single-copy gene that maps to the top arm of chromosome 5. Northern hybridization analysis of sulfate-starved plants indicated that the steady-state mRNA abundance of AST68 increased specifically in roots up to 9-fold by sulfate starvation. In situ hybridization experiments revealed that AST68 transcripts were accumulated in the central cylinder of sulfate-starved roots, but not in the xylem, endodermis, cortex, and epidermis. Among all the structural genes for sulfate assimilation, sulfate transporter (AST68), APS reductase (APR1), and serine acetyltransferase (SAT1) were inducible by sulfate starvation in A. thaliana. The sulfate transporter (AST68) exhibited the most intensive and specific response in roots, indicating that AST68 plays a central role in the regulation of sulfate assimilation in plants.
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Project description:We determined the solution structure of At3g28950 from A. thaliana, a homolog of At5g39720, whose structure we solved earlier. The secondary structure of the 165-aa protein consists of a 5-strand antiparallel beta-barrel domain flanked by two alpha-helices and a 2-strand beta-sheet; an additional free C-terminal alpha-helix extends into solution. Bioinformatic searches and analyses suggest that members of this growing set of structurally related proteins have been recruited to serve a wide variety of functions ranging from gamma-glutamyl cyclotransferase activity to participation in plant responses to chemical and biotic stimuli. Expression of a human homolog is elevated in bladder cancer tissues. Expression patterns for At3g28950 and its Arabidopsis paralogs suggest that each one evolved a different physiological role. The At3g28950 structure was solved as part of a structural genomics effort, and the results demonstrate how such a project can further understanding of genome evolution in addition to sequence-structure and structure-function relationships. Proteins 2008. (c) 2008 Wiley-Liss, Inc.
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Project description:Present in virtually every species, thioredoxins catalyze disulfide/dithiol exchange with various substrate proteins. While the human genome contains a single thioredoxin gene, plant thioredoxins are a complex protein family. A total of 19 different thioredoxin genes in six subfamilies has emerged from analysis of the Arabidopsis thaliana genome. Some function specifically in mitochondrial and chloroplast redox signaling processes, but target substrates for a group of eight thioredoxin proteins comprising the h subfamily are largely uncharacterized. In the course of a structural genomics effort directed at the recently completed A. thaliana genome, we determined the structure of thioredoxin h1 (At3g51030.1) in the oxidized state. The structure, defined by 1637 NMR-derived distance and torsion angle constraints, displays the conserved thioredoxin fold, consisting of a five-stranded beta-sheet flanked by four helices. Redox-dependent chemical shift perturbations mapped primarily to the conserved WCGPC active-site sequence and other nearby residues, but distant regions of the C-terminal helix were also affected by reduction of the active-site disulfide. Comparisons of the oxidized A. thaliana thioredoxin h1 structure with an h-type thioredoxin from poplar in the reduced state revealed structural differences in the C-terminal helix but no major changes in the active site conformation.
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