title: Phylogeny and a structural model of plant MHX transporters.
abstract: BACKGROUND
  The Arabidopsis thaliana MHX gene (AtMHX) encodes a Mg²⁺/H⁺ exchanger. Among non-plant proteins, AtMHX showed the highest similarity to mammalian Na⁺/Ca²⁺ exchanger (NCX) transporters, which are part of the Ca²⁺/cation (CaCA) exchanger superfamily.
  
  
  RESULTS
  Sequences showing similarity to AtMHX were searched in the databases or sequenced from cDNA clones. Phylogenetic analysis showed that the MHX family is limited to plants, and constitutes a sixth family within the CaCA superfamily. Some plants include, besides a full MHX gene, partial MHX-related sequences. More than one full MHX gene was currently identified only in Oryza sativa and Mimulus guttatus, but an EST for more than one MHX was identified only in M. guttatus. MHX genes are not present in the currently available chlorophyte genomes. The prevalence of upstream ORFs in MHX genes is much higher than in most plant genes, and can limit their expression. A structural model of the MHXs, based on the resolved structure of NCX1, implies that the MHXs include nine transmembrane segments. The MHXs and NCXs share 32 conserved residues, including a GXG motif implicated in the formation of a tight-turn in a reentrant-loop. Three residues differ between all MHX and NCX proteins. Altered mobility under reducing and non-reducing conditions suggests the presence of an intramolecular disulfide-bond in AtMHX.
  
  
  CONCLUSIONS
  The absence of MHX genes in non-plant genomes and in the currently available chlorophyte genomes, and the presence of an NCX in Chlamydomonas, are consistent with the suggestion that the MHXs evolved from the NCXs after the split of the chlorophyte and streptophyte lineages of the plant kingdom. The MHXs underwent functional diploidization in most plant species. De novo duplication of MHX occurred in O. sativa before the split between the Indica and Japonica subspecies, and was apparently followed by translocation of one MHX paralog from chromosome 2 to chromosome 11 in Japonica. The structural analysis presented and the identification of elements that differ between the MHXs and the NCXs, or between the MHXs of specific plant groups, can contribute to clarification of the structural basis of the function and ion selectivity of MHX transporters.
authors: The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 5290002, Israel
authors: Rachel
authors: R
authors: Gaash
authors: Meirav
authors: M
authors: Elazar
authors: Keren
authors: K
authors: Mizrahi
authors: Meital
authors: M
authors: Avramov-Mor
authors: Irina
authors: I
authors: Berezin
authors: Orit
authors: O
authors: Shaul
mesh_terms: D000595:Amino Acid Sequence; D017920:Antiporters / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019143:Evolution, Molecular; D018745:Genome, Plant; D008969:Molecular Sequence Data; D005810:Multigene Family; D010802:Phylogeny; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D010944:Plants / Q000737:chemistry / Q000145:classification* / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D017920:Antiporters; D029681:Arabidopsis Proteins; C120847:AtMHX protein, Arabidopsis; D010940:Plant Proteins
references: Proc Natl Acad Sci U S A. 1997 Jun 24;94(13):6809-14
references: 11038553
references: J Mol Biol. 1992 May 20;225(2):487-94
references: 1593632
references: BMC Evol Biol. 2007 Aug 02;7:130
references: 17683536
references: Proc Natl Acad Sci U S A. 1997 Sep 16;94(19):10249-54
references: 9294196
references: Plant Cell Environ. 2006 Jun;29(6):1179-90
references: 17080942
references: Physiol Genomics. 2005 Apr 14;21(2):161-73
references: 15741504
references: Biophys J. 2000 Aug;79(2):828-40
references: 10920015
references: Annu Rev Physiol. 2000;62:111-33
references: 10845086
references: Mol Plant. 2011 May;4(3):428-41
references: 21459829
references: Nucleic Acids Res. 1988 Nov 25;16(22):10881-90
references: 2849754
references: Plant Mol Biol. 2009 Nov;71(4-5):367-78
references: 19653106
references: Plant J. 2000 Nov;24(4):489-501
references: 11115130
references: Planta. 2007 Jan;225(2):403-11
references: 16845524
references: Funct Plant Biol. 2008 Feb;35(1):15-25
references: 32688753
references: Science. 2012 Feb 10;335(6069):686-90
references: 22323814
references: Nucleic Acids Res. 1987 Oct 26;15(20):8125-48
references: 3313277
references: Bioinformatics. 2007 Nov 1;23(21):2947-8
references: 17846036
references: J Gen Physiol. 1997 Feb;109(2):273-86
references: 9041455
references: Eur J Biochem. 1988 Jul 1;174(4):671-8
references: 3134198
references: Heredity (Edinb). 2008 Feb;100(2):220-30
references: 17551519
references: Annu Rev Cell Dev Biol. 2008;24:211-35
references: 18588487
references: J Biol Chem. 2001 Jun 1;276(22):18905-7
references: 11259419
references: Channels (Austin). 2008 Sep-Oct;2(5):322-8
references: 18989096
references: J Mol Evol. 2006 Dec;63(6):815-25
references: 17086450
references: J Biol Chem. 1994 Sep 9;269(36):22847-52
references: 8077237
references: Proc Natl Acad Sci U S A. 1993 May 1;90(9):3870-4
references: 8483905
references: J Exp Bot. 2005 Mar;56(413):1039-47
references: 15710632
references: Plant Cell. 2001 Dec;13(12):2761-75
references: 11752386
references: Mol Biol Evol. 2004 May;21(5):809-18
references: 14963099
references: Nat Methods. 2011 Sep 29;8(10):785-6
references: 21959131
references: BMC Evol Biol. 2008 Apr 30;8:127
references: 18447948
references: New Phytol. 2005 Jul;167(1):249-65
references: 15948847
references: Biochem J. 2007 Sep 15;406(3):365-82
references: 17716241
references: Proc Natl Acad Sci U S A. 2001 Aug 14;98(17):9660-5
references: 11493679
references: Plant Cell Rep. 2008 May;27(5):939-49
references: 18327593
references: Circ Res. 2001 May 11;88(9):864-76
references: 11348995
references: J Biol Chem. 1998 Jan 9;273(2):778-83
references: 9422731
references: Ann N Y Acad Sci. 2007 Mar;1099:7-15
references: 17347334
references: J Biol Chem. 2006 Aug 11;281(32):22808-14
references: 16785232
references: Biochim Biophys Acta. 1988 Nov 22;945(2):298-306
references: 3191125
references: J Biol Chem. 1996 Jun 7;271(23):13385-91
references: 8662775
references: Plant Physiol. 2001 Aug;126(4):1646-67
references: 11500563
references: J Biol Chem. 2000 Dec 8;275(49):38571-80
references: 10967097
references: Curr Protoc Cell Biol. 2002 May;Chapter 15:Unit 15.6
references: 18228398
references: Front Plant Sci. 2012 Jan 13;3:1
references: 22645563
references: Mol Biol Evol. 2011 Oct;28(10):2731-9
references: 21546353
references: Chromosome Res. 2009;17(5):699-717
references: 19802709
references: Physiology (Bethesda). 2008 Oct;23:275-85
references: 18927203
references: Curr Opin Plant Biol. 2003 Jun;6(3):263-7
references: 12753976
references: Proc Biol Sci. 1999 Jan 22;266(1415):163-71
references: 10097391
references: Plant J. 2009 Dec;60(6):1031-42
references: 19754518
references: J Biol Chem. 1999 Jan 8;274(2):910-7
references: 9873031
references: Am J Physiol Cell Physiol. 2004 Nov;287(5):C1167-72
references: 15475515
references: Science. 2012 Feb 10;335(6069):669-70
references: 22323810
references: Cell Calcium. 2009 Jan;45(1):1-10
references: 18614228
references: Genome Res. 2006 Jun;16(6):738-49
references: 16702410
references: Ann N Y Acad Sci. 1996 Apr 15;779:86-92
references: 8659884
references: Funct Plant Biol. 2006 Jul;33(7):661-672
references: 32689275
references: Science. 1990 Oct 26;250(4980):562-5
references: 1700476
references: J Gen Physiol. 1992 Dec;100(6):905-32
references: 1484285
references: J Biol Chem. 2000 Jan 7;275(1):182-8
references: 10617603
references: Plant Physiol. 1994 Sep;106(1):79-85
references: 12232305
references: Plant Mol Biol. 1997 Dec;35(6):993-1001
references: 9426620
references: Cell Mol Life Sci. 2010 Nov;67(22):3763-84
references: 20623158
references: Ann N Y Acad Sci. 2007 Mar;1099:1-6
references: 17303833
references: EMBO J. 1999 Jul 15;18(14):3973-80
references: 10406802
references: Evolution. 1985 Jul;39(4):783-791
references: 28561359
references: J Biol Chem. 1997 Feb 7;272(6):3190-4
references: 9013553
references: Mol Biol (Mosk). 2002 Jul-Aug;36(4):649-56
references: 12173469
references: Proc Natl Acad Sci U S A. 1999 Mar 30;96(7):3345-7
references: 10097041
references: New Phytol. 2010 Apr;186(1):37-45
references: 20002321
references: Gene. 2002 Oct 16;299(1-2):1-34
references: 12459250
references: Mol Biol Evol. 2004 Sep;21(9):1692-703
references: 15163769
references: Am J Physiol Cell Physiol. 2010 Mar;298(3):C407-29
references: 19940067
references: Proc Natl Acad Sci U S A. 2004 Jun 29;101(26):9903-8
references: 15161969
references: Microbiol Mol Biol Rev. 2000 Mar;64(1):13-33
references: 10704472
references: FEBS Lett. 1999 Mar 12;446(2-3):264-8
references: 10100855
references: Arch Biochem Biophys. 1991 Nov 1;290(2):369-75
references: 1929404
references: Science. 1998 Apr 3;280(5360):69-77
references: 9525859
references: Physiol Plant. 2010 Jul 1;139(3):303-12
references: 20210874
references: Comput Appl Biosci. 1992 Jun;8(3):275-82
references: 1633570
references: Mol Genet Genomics. 2004 Dec;272(5):504-11
references: 15503144
references: Plant Physiol. 1992 Sep;100(1):255-60
references: 16652955
references: Biometals. 2002 Sep;15(3):309-23
references: 12206396