Arabidopsis thaliana 'extra-large GTP-binding protein' (AtXLG1): a new class of G-protein

Plant Mol Biol. 1999 May;40(1):55-64. doi: 10.1023/a:1026483823176.


Heterotrimeric GTP-binding proteins, composed of alpha, beta, and gamma subunits, are involved in signal transduction pathways in animal and plant systems. In plants, physiological analyses implicate heterotrimeric G-proteins in ion channel regulation, light signaling, and hormone and pathogen responses. However, only one class of plant G alpha genes has been identified to date. We have cloned a novel gene, 'Arabidopsis thaliana extra-large GTP-binding protein' (AtXLG1). AtXLG1 appears to be a member of a small gene family and is transcribed in all tissues assayed: roots, leaves, stems, flowers, and fruits. The conceptually translated protein from AtXLG1 is 99 kDa, twice as large as typical G alpha proteins. The carboxy-terminal half of the AtXLG1 protein has significant homology to animal and plant G alpha proteins. This region includes a GTP-binding domain, a predicted helical domain, and an aspartate/glutamate-rich loop, which are characteristics of G alpha's. Despite the absence of some of the amino acids implicated in GTP binding and hydrolysis by crystallographic and mutational analyses of mammalian G alpha's, recombinant AtXLG1 binds GTP with specificity. The amino-terminal region of AtXLG1 contains domains homologous to the bacterial TonB-box, which is involved in energy transduction between the inner and outer bacterial membranes, and to zinc-finger proteins. Given the unique structure of AtXLG1, it will be of interest to uncover its physiological functions.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Arabidopsis / genetics*
  • Arabidopsis Proteins*
  • Bacterial Proteins
  • Conserved Sequence
  • Cysteine
  • DNA, Complementary / genetics
  • Evolution, Molecular
  • GTP-Binding Proteins / classification*
  • GTP-Binding Proteins / genetics*
  • Genes, Plant
  • Genomic Library
  • Guanosine Triphosphate / metabolism*
  • Membrane Proteins
  • Molecular Sequence Data
  • Plant Proteins / classification
  • Plant Proteins / genetics
  • Sequence Homology, Amino Acid


  • Arabidopsis Proteins
  • Bacterial Proteins
  • DNA, Complementary
  • Membrane Proteins
  • Plant Proteins
  • XLG1 protein, Arabidopsis
  • tonB protein, Bacteria
  • Guanosine Triphosphate
  • GTP-Binding Proteins
  • Cysteine

Associated data

  • GENBANK/AF060941
  • GENBANK/AF060942