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ID 39961
file
creator
Michibata, Hitoshi
subject
Membrane protein
Transport metals
Vanadium
Ascidian
NDC
Biology
abstract
Background: Vanadium is an essential transition metal in biological systems. Several key proteins related to vanadium accumulation and its physiological function have been isolated, but no vanadium ion transporter has yet been identified.

Methods: We identified and cloned a member of the Nramp/DCT family of membrane metal transporters (AsNramp) from the ascidian Ascidia sydneiensis samea, which can accumulate extremely high levels of vanadium in the vacuoles of a type of blood cell called signet ring cells (also called vanadocytes). We performed immunological and biochemical experiments to examine its expression and transport function.

Results: Western blotting analysis showed that AsNramp was localized at the vacuolar membrane of vanadocytes. Using the Xenopus oocyte expression system, we showed that AsNramp transported VO2+ into the oocyte as pH-dependent manner above pH 6, while no significant activity was observed below pH 6. Kinetic parameters (Km and Vmax) of AsNramp-mediated VO2+ transport at pH 8.5 were 90 nM and 9.1 pmol/oocyte/h, respectively. A rat homolog, DCT1, did not transport VO2+ under the same conditions. Excess Fe2+, Cu2+, Mn2+ or Zn2+ inhibited the transport of VO2+.

Conclusions: AsNramp was revealed to be a novel VO2+/H+ antiporter, and we propose that AsNramp mediates vanadium accumulation coupled with the electrochemical gradient generated by vacuolar H+-ATPase in vanadocytes.

General Significance: This is the first report of identification and functional analysis on a membrane transporter for vanadium ions.
description
This work was supported in part by Grants-in-Aid from the Ministry of Education, Culture, Sports, Science and Technology, Japan (#17370026, #18570070, #20570070, and #21570077).
journal title
Biochimica et Biophysica Acta (BBA) - General Subjects
volume
Volume 1810
issue
Issue 4
start page
457
end page
464
date of issued
2011-04
publisher
Elsevier B.V.
issn
0304-4165
ncid
publisher doi
language
eng
nii type
Journal Article
HU type
Journal Articles
DCMI type
text
format
application/pdf
text version
author
rights
Copyright (c) 2011 Elsevier B.V. All rights reserved.
This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/
relation is version of URL
http://doi.org/10.1016/j.bbagen.2010.12.006
department
Graduate School of Science