Cao, Z., Van Lith, M., Mitchell, L. J., Pringle, M. A. , Inaba, K. and Bulleid, N. J. (2016) The membrane topology of vitamin K epoxide reductase is conserved between human isoforms and the bacterial enzyme. Biochemical Journal, 473(7), pp. 851-858. (doi: 10.1042/bj20151223) (PMID:26772871)
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Abstract
The membrane topology of vitamin K epoxide reductase (VKOR) is controversial with data supporting both a three transmembrane and a four transmembrane model. The positioning of the transmembrane domains and the loops between these domains is critical if we are to understand the mechanism of vitamin K oxidation and its recycling by members of the thioredoxin family of proteins and the mechanism of action of warfarin, an inhibitor of VKOR. Here we show that both mammalian VKOR isoforms adopt the same topology, with the large loop between transmembrane one and two facing the lumen of the endoplasmic reticulum (ER). We used a redox sensitive green fluorescent protein (GFP) fused to the N- or C-terminus to show that these regions face the cytosol, and introduction of glycosylation sites along with mixed disulfide formation with thioredoxin-like transmembrane protein (TMX) to demonstrate ER localization of the major loop. The topology is identical with the bacterial homologue from Synechococcus sp., for which the structure and mechanism of recycling has been characterized. Our results provide a resolution to the membrane topology controversy and support previous results suggesting a role for members of the ER protein disulfide isomerase (PDI) family in recycling VKOR.
Item Type: | Articles |
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Status: | Published |
Refereed: | Yes |
Glasgow Author(s) Enlighten ID: | Van Lith, Dr Marcel and Cao, Dr Zhenbo and Bulleid, Professor Neil and Pringle, Mrs Marie and Mitchell, Mrs Lorna |
Authors: | Cao, Z., Van Lith, M., Mitchell, L. J., Pringle, M. A., Inaba, K., and Bulleid, N. J. |
College/School: | College of Medical Veterinary and Life Sciences > School of Molecular Biosciences |
Journal Name: | Biochemical Journal |
Publisher: | Portland Press Ltd. |
ISSN: | 0264-6021 |
ISSN (Online): | 1470-8728 |
Published Online: | 15 January 2016 |
Copyright Holders: | Copyright © 2016 The Authors |
First Published: | First published in Biochemical Journal 473(7):851-858 |
Publisher Policy: | Reproduced in accordance with the copyright policy of the publisher |
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