Identification of Three Distinct Phylogenetic Groups of CAX Cation/Proton Antiporters |
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Authors: | T Shigaki I Rees L Nakhleh KD Hirschi |
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Institution: | (1) Children’s Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Room 9016, CNRC, 1100 Bates Street, Houston, TX 77030, USA;(2) Department of Computer Science, Rice University, Houston, TX 77005, USA |
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Abstract: | Ca2+/cation antiporter (CaCA) proteins are integral membrane proteins that transport Ca2+ or other cations using the H+ or Na+ gradient generated by primary transporters. The CAX (for CAtion eXchanger) family is one of the five families that make up
the CaCA superfamily. CAX genes have been found in bacteria, Dictyostelium, fungi, plants, and lower vertebrates, but only a small number of CAXs have been functionally characterized. In this study,
we explored the diversity of CAXs and their phylogenetic relationships. The results demonstrate that there are three major
types of CAXs: type I (CAXs similar to Arabidopsis thaliana CAX1, found in plants, fungi, and bacteria), type II (CAXs with a long N-terminus hydrophilic region, found in fungi, Dictyostelium, and lower vertebrates), and type III (CAXs similar to Escherichia coli ChaA, found in bacteria). Some CAXs were found to have secondary structures that are different from the canonical six transmembrane
(TM) domains–acidic motif-five TM domain structure. Our phylogenetic tree indicated no evidence to support the cyanobacterial
origin of plant CAXs or the classification of Arabidopsis exchangers CAX7 to CAX11. For the first time, these results clearly define the CAX exchanger family and its subtypes in phylogenetic
terms. The surprising diversity of CAXs demonstrates their potential range of biochemical properties and physiologic relevance.
Electronic Supplementary Material Electronic Supplementary material is available for this article at
and accessible for authorised users.
Reviewing Editor: David Guttman] |
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Keywords: | Calcium/proton antiporter Cation homeostasis Cation/proton antiporter CAX Membrane protein Phylogeny |
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