Identification of a Novel Vanadium-binding Protein by EST Analysis on the Most Vanadium-rich Ascidian, Ascidia gemmata

Abstract

Ascidians are known to accumulate extremely high levels of vanadium in their blood cells (up to 350 mM). The branchial sac and the intestine are thought to be the first tissues to contact the outer environment and absorb vanadium ions. The concentration of vanadium in the branchial sac and the intestine of the most vanadium-rich ascidian Ascidia gemmata were determined to be 32.4 and 11.9 mM, respectively. Using an expressed sequence tag (EST) analysis of a cDNA library from the intestine of A. gemmata, we determined 960 ESTs and found 55 clones of metal-related gene orthologs, 6 redox-related orthologs, and 18 membrane transporter orthologs. Among them, two genes, which exhibited significant similarity to the vanadium-binding proteins of other vanadium-rich ascidian species, were designated AgVanabin1 and AgVanabin2. Immobilized metal ion affinity chromatography revealed that recombinant AgVanabin1 bound to metal ions with an increasing affinity for Cu(II)> Zn(II) > Co(II) and AgVanabin2 bound to metal ions with an increasing affinity for Cu(II) > Fe(III) > V(IV). To examine the use of AgVanabins for a metal absorption system, we constructed Escherichia coli strains that expressed AgVanabin1 or AgVanabin2 fused to maltose-binding protein and secreted into the periplasmic space. We found that the strain expressing AgVanabin2 accumulated about 13.5 times more Cu(II) ions than the control TB1 strain. Significant accumulation of vanadium was also observed in the AgVanabin2-expressing strain as seen by a 1.5-fold increase.

Vanadium-Binding Ability of Nucleoside Diphosphate Kinase from the Vanadium-Rich Fan Worm, Pseudopotamilla occelata

“…Although vanabin-like proteins were not found in the fan worm, NDK appeared frequently in the expressed sequence tags from the vanadiumaccumulating ascidian Ascidia gemmata (Samino et al, 2012). NDK is present in both species, and may therefore play a certain role in vanadium accumulation.…”

“…Extensive efforts have been made to identify vanadium-binding proteins from vanadium-rich ascidians. Ion exchange column chromatography and immobilized metal ion affinity chromatography (IMAC) have been used in the identification of vanadium-binding proteins (Ueki et al, 2003a;Trivedi et al, 2003;Yamaguchi et al, 2004;Yoshihara et al, 2005Yoshihara et al, , 2008Yoshinaga et al, 2006;Michibata et al, 2007;Samino et al, 2012). The most prominent family of such proteins is the vanabins, which are novel vanadium-binding proteins ubiquitously found among vanadium-accumulating ascidians.…”

Vanadium-binding protein from vanadium-enriched sea cucumber Apostichopus japonicus inhibits adipocyte differentiation through activating WNT/β-catenin pathway

“…An important role of vanadium in marine organisms is being an active centre of enzymes, such as the vanadium bromoperoxidase of some ocean algae (Clague, Keder, & Butler, 1993), but its precise role and mechanism in mammals remains to be studied. The concentration of vanadium in the intestine of the most vanadium-rich ascidian Ascidia gemmata was reported to be 11.9 mM by Samino (2012). Sea cucumbers have been reported to be vanadium accumulators, and the average values of 1.09 µg g −1 of total vanadium and 0.79 µg g −1 of organic vanadium were obtained in the intestine and blood of sea cucumbers (Liu, Zhou, et al, 2015).…”

Bioaccumulation of Vanadium by Vanadium-Resistant Bacteria Isolated from the Intestine of Ascidia sydneiensis samea

“…Ascidians, also known as sea squirts or tunicates, can accumulate a high level of vanadium ions in blood cells (Ueki and Michibata 2011;Michibata 2012;Ueki et al 2014).…”

“…The intestinal organ of an ascidian is tough to be first location to contact with outer environment and absorbs vanadium ions. Intestinal organ of vanadium-rich ascidian, Ascidia gemmata, accumulated 11.9 mM of vanadium ions before stored in highest concentration in blood cell (Samino et al 2012). Intestinal organ also harbors several types of bacteria as reported by Dishaw et al (2014) that bacterial communities isolated from the gut of an ascidian, Ciona intestinalis, obtained from three disparate geographic locations exhibited striking similarity in the abundance of operational taxonomic units (OTUs), consistent with the selection of a core community by the gut ecosystem, in which Proteobacteria (80%) were the predominant gut bacteria.…”