Evidence for the biosynthesis of selenobiotin

Lindblow-Kull, Carole; Kull, F. Jon; Shrift, Alex

doi:10.1016/0006-291x(80)91115-8

Cited by 10 publications

(4 citation statements)

References 20 publications

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“…Its main edge energy is positioned between the values typical for Se 0 and Se +4 [34,36], with distances that fully correspond to those obtained in the paper of Van No changes have been observed in the spectra of the mycelium treated with 10 mM Se +6 , suggesting that the mycelium does not have a capacity for its transformation. This is in collision with previous work of Lindblow-Kull [41] who has shown synthesis of selenobiotin by P. blakesleeanus with the addition of Se +6 , albeit different medium and culture conditions were applied.…”

Section: Resultssupporting

confidence: 55%

Biotransformation of selenium in the mycelium of the fungus Phycomyces blakesleeanus

et al. 2022

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Biotransformation of toxic selenium ions to non-toxic species has been mainly focused on biofortification of microorganisms and production of selenium nanoparticles (SeNPs), while far less attention is paid to the mechanisms of transformation. In this study, mycelium of fungus Phycomyces blakesleeanus was exposed to selenite (Se +4 ) to examine its ability to reduce Se +4 to nanoparticles, as well as to elucidate the mechanisms of reduction itself. Red coloration and pungent odor that appeared after only a few hours of incubation with 10 mM Se +4 indicate formation of SeNPs and volatile methylated selenium compounds. SEM-EDS confirmed pure selenium NPs with an average diameter of 57 nm, which indicates to potentially very good medical, optical and photoelectric characteristics. XANES spectroscopy of mycelium revealed concentration dependent mechanisms of reduction, where 0.5 mM Se +4 led to predominant formation of Se-S containing organic molecules, while 10 mM Se +4 induced production of biomethylated selenide (Se -2 ) in the form of volatile dimethylselenide (DMSe) and selenium nanoparticles (SeNPs), with SeNPs/DMSe ratio rising with incubation time. Several structural forms of elemental selenium were detected, predominantly monoclinic Se 8 chains, together with trigonal Se polymer chain, Se 8 and Se 6 ring structures.

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Section: Resultssupporting

confidence: 55%

Biotransformation of selenium in the mycelium of the fungus Phycomyces blakesleeanus

et al. 2022

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“…The sulfate ABC transporter of Escherichia coli mediates selenite uptake in addition to that of selenate (4). However, repression of the expression of that transporter does not quench selenite uptake completely, indicating that an alternative entry pathway exists for selenite (5).…”

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confidence: 99%

Uptake of Selenite by Saccharomyces cerevisiae Involves the High and Low Affinity Orthophosphate Transporters

Lazard

Blanquet

Fisicaro

et al. 2010

Journal of Biological Chemistry

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Although the general cytotoxicity of selenite is well established, the mechanism by which this compound crosses cellular membranes is still unknown. Here, we show that in Saccharomyces cerevisiae, the transport system used opportunistically by selenite depends on the phosphate concentration in the growth medium. Both the high and low affinity phosphate transporters are involved in selenite uptake. When cells are grown at low P i concentrations, the high affinity phosphate transporter Pho84p is the major contributor to selenite uptake. When phosphate is abundant, selenite is internalized through the low affinity P i transporters (Pho87p, Pho90p, and Pho91p). Accordingly, inactivation of the high affinity phosphate transporter Pho84p results in increased resistance to selenite and reduced uptake in low P i medium, whereas deletion of SPL2, a negative regulator of low affinity phosphate uptake, results in exacerbated sensitivity to selenite. Measurements of the kinetic parameters for selenite and phosphate uptake demonstrate that there is a competition between phosphate and selenite ions for both P i transport systems. In addition, our results indicate that Pho84p is very selective for phosphate as compared with selenite, whereas the low affinity transporters discriminate less efficiently between the two ions. The properties of phosphate and selenite transport enable us to propose an explanation to the paradoxical increase of selenite toxicity when phosphate concentration in the growth medium is raised above 1 mM.Although toxic at high concentrations, selenium is required in many cells, because it is translationally incorporated as selenocysteine into selenoproteins that perform specific and essential functions (1). Cells must ensure selenium uptake to sustain this metabolism. However, little is known about selenium transport. Because selenium and sulfur are chalcogen elements that have many chemical properties in common, selenium shares metabolic pathways with sulfur. Accordingly, selenate was shown to be taken up by the yeast Saccharomyces cerevisiae sulfate permeases (2). Similarly, in plants, selenate is taken up by roots via the high affinity sulfate transporters (3).On the other hand, specific selenite transporters have never been identified so far. The sulfate ABC transporter of Escherichia coli mediates selenite uptake in addition to that of selenate (4). However, repression of the expression of that transporter does not quench selenite uptake completely, indicating that an alternative entry pathway exists for selenite (5). In S. cerevisiae, which does not possess selenoproteins, an energy-dependent uptake of selenite, distinct from that of selenate, was reported. Characterization of the kinetics of selenite uptake suggested the existence of two transport systems: a high affinity system at low selenite concentration and a low affinity system at higher concentration (6). Recently, a study of selenite uptake by wheat (Triticum aestivum) roots showed it to be an active process competitively inhibited by phosph...

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“…Selenobiotin is a natural substance which has been characterized as an excretion product of the fungus Phycomyces blakesleeanus (5), and one would expect that it has been produced by biotin synthase, using the same mechanism. We decided to investigate this reaction in vitro.…”

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confidence: 99%

Escherichia coli Biotin Synthase Produces Selenobiotin. Further Evidence of the Involvement of the [2Fe-2S]²⁺ Cluster in the Sulfur Insertion Step

et al. 2006

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Biotin synthase, a member of the "radical SAM" family, catalyzes the final step of the biotin biosynthetic pathway, namely, the insertion of a sulfur atom into dethiobiotin. The as-isolated enzyme contains a [2Fe-2S](2+) cluster, but the active enzyme requires an additional [4Fe-4S](2+) cluster, which is formed in the presence of Fe(NH(4))(2)(SO(4))(2) and Na(2)S in the in vitro assay. The role of the [4Fe-4S](2+) cluster is to mediate the electron transfer to SAM, while the [2Fe-2S](2+) cluster is involved in the sulfur insertion step. To investigate the selenium version of the reaction, we have depleted the enzyme of its iron and sulfur and reconstituted the resulting apoprotein with FeCl(3) and Na(2)Se to yield a [2Fe-2Se](2+) cluster. This enzyme was assayed in vitro with Na(2)Se in place of Na(2)S to enable the formation of a [4Fe-4Se](2+) cluster. Selenobiotin was produced, but the activity was lower than that of the as-isolated [2Fe-2S](2+) enzyme in the presence of Na(2)S. The [2Fe-2Se](2+) enzyme was additionally assayed with Na(2)S, to reconstitute a [4Fe-4S](2+) cluster, in case the latter was more efficient than a [4Fe-4Se](2+) cluster for the electron transfer. Indeed, the activity was improved, but in that case, a mixture of biotin and selenobiotin was produced. This was unexpected if one considers the [2Fe-2S](2+) center as the sulfur source (either as the ultimate donor or via another intermediate), unless some exchange of the chalcogenide has taken place in the cluster. This latter point was seen in the resonance Raman spectrum of the reacted enzyme which clearly indicated the presence of both the [2Fe-2Se](2+) and [2Fe-2S](2+) clusters. No exchange was observed in the absence of reaction. These observations bring supplementary proof that the [2Fe-2S](2+) cluster is implicated in the sulfur insertion step.

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Evidence for the biosynthesis of selenobiotin

Cited by 10 publications

References 20 publications

Biotransformation of selenium in the mycelium of the fungus Phycomyces blakesleeanus

Biotransformation of selenium in the mycelium of the fungus Phycomyces blakesleeanus

Uptake of Selenite by Saccharomyces cerevisiae Involves the High and Low Affinity Orthophosphate Transporters

Escherichia coli Biotin Synthase Produces Selenobiotin. Further Evidence of the Involvement of the [2Fe-2S]²⁺ Cluster in the Sulfur Insertion Step

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Evidence for the biosynthesis of selenobiotin

Cited by 10 publications

References 20 publications

Biotransformation of selenium in the mycelium of the fungus Phycomyces blakesleeanus

Biotransformation of selenium in the mycelium of the fungus Phycomyces blakesleeanus

Uptake of Selenite by Saccharomyces cerevisiae Involves the High and Low Affinity Orthophosphate Transporters

Escherichia coli Biotin Synthase Produces Selenobiotin. Further Evidence of the Involvement of the [2Fe-2S]2+ Cluster in the Sulfur Insertion Step

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Escherichia coli Biotin Synthase Produces Selenobiotin. Further Evidence of the Involvement of the [2Fe-2S]²⁺ Cluster in the Sulfur Insertion Step