Department of Biological Sciences, George Washington University
Soybean and Alfalfa Research Laboratory, United States Department of Agriculture, Agricultural Research Service, Beltsville, Maryland
Animal ionotropic glutamate receptors (iGLRs) and members of subfamily C (Kolakowski 1994
) or IV (Parmentier et al. 1998
) of the G-protein-coupled receptors (subC-GPCRs), which contains the metabotropic glutamate receptors (mGLRs) and
-aminobutyric acidB receptors (GABA-BRs), have distinct pharmacological and structural characteristics (Sutcliffe, Wo, and Oswald 1996
; Walker, Brooks, and Holden-Dye 1996
; Sutcliffe et al. 1998
). Likeness among members of the two superfamilies has been noted in the literature. The iGLRs share sequence similarity with regions of the mGLRs (Walker, Brooks, and Holden-Dye 1996
), and mGLRs share sequence similarity with GABA-BRs (Kaupmann et al. 1997
). In addition, all of the receptors, iGLRs (Wo and Oswald 1995
), mGLRs (O'Hara et al. 1993
), and GABA-BRs (Galvez et al. 1999
), have sequence similarities to portions of the bacterial periplasmic binding proteins. An evolutionary link between the iGLRs and the periplasmic binding proteins has been demonstrated (Chiu et al. 1999
) via a newly identified family of genes encoding for putative GLRs in plants (Lam et al. 1998
). Despite the noted similarities among the iGLRs and members of subC-GPCRs, namely, the mGLRS or GABA-BRs, there are no data to support an evolutionary link between any member of the two superfamilies, including one between members of the mGLRs and iGLRs (Walker, Brooks, and Holden-Dye 1996
). We provide evidence for a link between the iGLRs and members of subC-GPCRs by incongruence length difference, parsimony, and bootstrap analyses. We demonstrate that the N-terminal regions of the putative GLRs from plants are related to members of subC-GPCRs and that the C-terminal regions of the putative GLRs from plants are related to iGLRs. From this discordant relationship, we conclude that the ancestors of the plant GLRs may be the evolutionary progenitors of members of both superfamilies of highly specialized animal receptors via distinct evolutionary mechanisms. A model outlining the evolution of the receptors is presented.
Parsimony and bootstrap analyses have been used to provide evidence that plant GLRs and iGLRs shared a common ancestor prior to the divergence of iGLRs, including N-methyl-d-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate/kainate (AMPA/KA) subtypes (Chiu et al. 1999
). We used a similar approach to examine relationships between the putative GLRs from plants and members of two superfamilies of animal neurotransmitter receptors, the iGLRs and members of subC-GPCRs, specifically the mGLRs and GABA-BRs.
Based on our preliminary results from BLAST (Altschul et al. 1997
) and PHI-BLAST (Zhang et al. 1998
) searches (data not shown), we considered the possibility of a recombination event during the evolutionary history of the loci. To test this hypothesis, we conducted an incongruence length difference analysis (Farris et al. 1994, 1995
) in which we compared the relatedness of the approximate first third (N-terminal regions), and the last two thirds (C-terminal regions) of the peptides separately. In an analysis that contained members of the iGLRs, mGLRs, GABA-BRs, and plant GLRs, there was a significant difference (P = 0.001) in the relatedness of the two portions of the peptide, whereas there was not a significant difference (P > 0.1) when the plant GLRs were removed. Furthermore, these results are supported by results from parsimony analysis in which the N- and C-termini of the putative plant receptors were separated (fig. 1
). The C-terminal regions of the plant GLRs are related to members of the iGLRs. It can be concluded that the C-terminal regions of the GLRs and iGLRs arose from an ancestral locus that predated the divergence of animal AMPA/KA and NMDA receptors. These results are in agreement with those from a recently published analysis (Chiu et al. 1999
). However, our analyses of the N-terminal regions support a different scenario. The N-terminal regions of the Arabidopsis GLRs are related to GABA-BRs, which are members of the subC-GPCRs, and not to members of the iGLRs. The results of both the incongruence length difference and the parsimony analyses support the occurrence of a recombination event at the GLR locus. We conclude that the extant iGLRs and members of subC-GPCRs evolved from ancestral plant GLRs via distinct mechanisms. The iGLRs arose via a series of point mutations and selection, whereas the members of subC-GPCRs arose from a gene conversion or recombination event.
|
A proposed phylogenetic reconstruction (fig. 2 ) demonstrates the relationships among members of the superfamilies and the proposed recombination event. We proposed that an ancestral GLR was the precursor to the iGLRs and members of subC-GPCRs. The iGLRs arose via a series of point mutations and selection, whereas members of subC-GPCRs arose from a gene conversion or recombination event between an ancestral GLR locus and a gene encoding for a protein that contains seven-transmembrane domains, a GPCR-like locus. In summary, the ancestors of the extant GLRs are the evolutionary progenitors of both the iGLRs and members of subC-GPCRs via distinct mechanisms, and thus this finding represents the previously unidentified evolutionary link between the two superfamilies of animal neurotransmitter receptors.
|
Acknowledgements
We thank Drs. Robert Donaldson, Benjamin Matthews, and Alan Kinnersley for their critical review of this manuscript. F.J.T. gratefully acknowledges financial support from the Auxein Corporation, Lansing, Michigan.
Footnotes
Jeffrey C. Long, Reviewing Editor
1 Present address: Department of Pharmacology, University of Tennessee, Memphis, Tennessee.
1 Abbreviations: GABA-BRs, -aminobutyric acidB receptors; iGLRs, ionotropic glutamate receptors; mGLRs, metabotropic glutamate receptors; subC-GPCRs, subfamily C of the G-protein-coupled receptors.
2 Keywords: Arabidopsis
G-protein-coupled receptor
GABA receptor
gene conversion
glutamate receptor
incongruence length difference
recombination event
3 Address for correspondence and reprints: Frank J. Turano, Department of Biological Sciences, George Washington University, 2030 G Street, NW, Lisner Hall, Room 340, Washington, D.C. 20052. E-mail: fturano{at}gwu.edu
References
Altschul S. F., T. L. Madden, A. A. Schaffer, J. Zhang, Z. Zhang, W. Miller, D. J. Lipman, 1997 Gapped BLAST and PSI-BLAST: a new generation of protein database search programs Nucleic Acids Res 25:3389-3402
Chiu J., R. DeSalle, H.-M. Lam, L. Meisel, G. Coruzzi, 1999 Molecular evolution of glutamate receptors: a primitive signaling mechanism that existed before plants and animals diverged Mol. Biol. Evol 16:826-838[Abstract]
Farris J. S., M. Kallersjo, A. G. Kluge, C. Bult, 1994 Testing the significance of incongruence Cladistics 10:315-320[ISI]
. 1995 Constructing a significance test for incongruence Syst. Biol 44:570-522[ISI]
Galvez T., M. L. Parmentier, C. Joly, B. Malitschek, K. Kaupmann, R. Kuhn, H. Bittiger, W. Froestl, B. Bettler, J. P. Pin, 1999 Mutagenesis and modeling of the GABAB receptor extracellular domain support a venus flytrap mechanism for ligand binding J. Biol. Chem 274:13362-13369
Josefsson L. G., 1999 Evidence for kinship between diverse G-protein coupled receptors Gene 239:333-340[ISI][Medline]
Josefsson L. G., L. Rask, 1997 Cloning of a putative G-protein-coupled receptor from Arabidopsis thaliana Eur. J. Biochem 249:415-420[Abstract]
Kaupmann K., K. Huggel, J. Heid, et al. (11 co-authors) 1997 Expression cloning of GABA(B) receptors uncovers similarity to metabotropic glutamate receptors Nature 386:239-246[ISI][Medline]
Kolakowski L. F., 1994 GCRDb: a G-protein-coupled receptor database Receptors Channels 2:1-7[ISI][Medline]
Lam H.-M., J. Chiu, H.-H. Hsieh, L. Meisel, I. C. Oliveira, M. Shin, G. Coruzzi, 1998 Glutamate-receptor genes in plants Nature 396:125-126[ISI][Medline]
O'Hara P. J., P. O. Sheppard, H. Thogersen, D. Venezia, B. A. Haldeman, V. McGrane, K. M. Houame, C. Thomsen, T. L. Gilbert, E. R. Mulvihill, 1993 The ligand-binding domain in metabotropic glutamate receptors is related to bacterial periplasmic binding proteins Neuron 11:41-52[ISI][Medline]
Parmentier M. L., C. Joly, S. Restituito, J. Bockaert, Y. Grau, J. P. Pin, 1998 The G protein-coupling profile of metabotropic glutamate receptors, as determined with exogenous G proteins, is independent of their ligand recognition domain Mol. Pharmacol 53:778-786
Plakidou-Dymock S., D. Dymock, R. Hooley, 1998 A higher plant seven-transmembrane receptor that influences sensitivity to cytokinins Curr. Biol 8:315-324[ISI][Medline]
Sutcliffe M. J., A. H. Smeeton, Z. G. Wo, R. Oswald, 1998 Three-dimensional models of glutamate receptors Biochem. Soc. Trans 26:450-458[ISI][Medline]
Sutcliffe M. J., Z. G. Wo, R. Oswald, 1996 Three-dimensional models of non-NMDA glutamate receptors Biophys. J 70:1575-1589[Abstract]
Walker R. J., H. L. Brooks, L. Holden-Dye, 1996 Evolution and overview of classical transmitter molecules and their receptors Parasitology 113:(Suppl.)S3-S33[ISI][Medline]
Wo Z. G., R. Oswald, 1995 Unraveling the modular design of glutamate-gated ion channels Trends Neurosci 18:161-168[ISI][Medline]
Zhang Z., A. A. Schaffer, W. Miller, T. L. Madden, D. J. Lipman, E. V. Koonin, S. F. Altschul, 1998 Protein sequence similarity searches using patterns as seeds Nucleic Acids Res 26:3986-3990