Metal-binding domains and the metal selectivity of the vanadium(IV)-binding protein VBP-129 in blood plasma

Abstract

Ascidians are well known to accumulate extremely high levels of vanadium in their blood cells. Several key proteins related to vanadium accumulation and physiological function have been isolated from vanadium-rich ascidians. Of these, vanadium(IV)-binding protein-129 (VBP-129) is a unique protein that has been identified from the blood plasma of an ascidian Ascidia sydneiensis samea, but its metal binding domains are not known. In this study, several deletion and point mutants of VBP-129 were generated, and their metal binding abilities were assessed by immobilized metal ion affinity chromatography (IMAC) and electron spin resonance spectroscopy (ESR). The internal partial protein, VBP-Int41, did not bind to V(IV), but the two constructs, VBP-N52 and VBP-Int55, added with additional 11 or 14 neighboring amino acids bound to V(IV). Mutations for cysteine-47 and lysine-50 in VBP-Int55 diminished V(IV)-binding in VBP-Int55, suggesting that these amino acid residues play important roles in binding V(IV). ESR titration analysis revealed that VBP-129, VBP-N52 and VBP-Int55 could bind to 6, 3 and 2 V(IV) ions, respectively. ESR spectrum analysis indicated a N(2)O(2) coordination geometry, which is similar to vanabins. The cysteines may contribute to the maintenance of the three-dimensional structure that is necessary for binding V(IV) ions. VBP-129 did not have a V(V)-reductase activity, as expected from its tissue localization in blood plasma. This study provided the evidences that VBP-129 possesses V(IV)-binding domains that make a similar coordination to V(IV) as those by vanabins but VBP-129 acts solely as a V(IV)-chaperon in blood plasma.

Synthesis, characterization, antioxidant and anti‐diabetic activities of a novel protein–vanadium complex

“…The protein–vanadium complex was synthesized according to the method suggested by Ueki et al . with some modification.…”

Antioxidant and antidiabetic activities of vanadium‐binding protein and trifuhalol A

“…Therefore, the natural VBP from ascidians were attracted widespread attention (Ueki et al, 2003). It has been reported that the highest concentration of vanadium in Ascidia gemmata (350 mM) was approximate 1 × 10 7 times higher than that in natural seawater (Fukui et al, 2003;Ueki et al, 2012). In the previous study, the VBP from sea squirt Halocynthia roretzi, which is a traditional tonic food in Korea and Japan, exhibited strong inhibitory activity against a-glucosidase and adipocyte differentiation (Gunasinghe & Kim, 2018;Liu et al, 2015).…”