Do plants contain g protein-coupled receptors?
Whether G protein-coupled receptors (GPCRs) exist in plants is a fundamental biological question. Interest in deorphanizing new GPCRs arises because of their importance in signaling. Within plants, this is controversial, as genome analysis has identified 56 putative GPCRs, including G protein-coupled receptor1 (GCR1), which is reportedly a remote homolog to class A, B, and E GPCRs. Of these, GCR2 is not a GPCR; more recently, it has been proposed that none are, not even GCR1. We have addressed this disparity between genome analysis and biological evidence through a structural bioinformatics study, involving fold recognition methods, from which only GCR1 emerges as a strong candidate. To further probe GCR1, we have developed a novel helix-alignment method, which has been benchmarked against the class A-class B-class F GPCR alignments. In addition, we have presented a mutually consistent set of alignments of GCR1 homologs to class A, class B, and class F GPCRs and shown that GCR1 is closer to class A and/or class B GPCRs than class A, class B, or class F GPCRs are to each other. To further probe GCR1, we have aligned transmembrane helix 3 of GCR1 to each of the six GPCR classes. Variability comparisons provide additional evidence that GCR1 homologs have the GPCR fold. From the alignments and a GCR1 comparative model, we have identified motifs that are common to GCR1, class A, B, and E GPCRs. We discuss the possibilities that emerge from this controversial evidence that GCR1 has a GPCR fold.
School of Biological Sciences , University of Essex, Colchester, CO4 3SQ United Kingdom.
Bruck
B
Taddese
Graham J G
GJ
Upton
Gregory R
GR
Bailey
Siân R D
SR
Jordan
Nuradin Y
NY
Abdulla
Philip J
PJ
Reeves
Christopher A
CA
Reynolds
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins / Q000737:chemistry; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry*; D011487:Protein Conformation; D017510:Protein Folding; D043562:Receptors, G-Protein-Coupled / Q000737:chemistry*; D016415:Sequence Alignment / Q000379:methods; D017386:Sequence Homology, Amino Acid
D029681:Arabidopsis Proteins; C112029:GCR1 protein, Arabidopsis; D020662:Guanine Nucleotide Exchange Factors; D010940:Plant Proteins; D043562:Receptors, G-Protein-Coupled