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MBE Advance Access published online on October 8, 2008
Molecular Biology and Evolution, doi:10.1093/molbev/msn228
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© The Author 2008. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Research Article

The Secretin GPCRs descended from the family of Adhesion GPCRs

Karl J. V. Nordströma, Malin C. Lagerströma,b, Linn M. J. Walléra, Robert Fredrikssona and Helgi B. Schiötha

a Department of Neuroscience, Functional Pharmacology, Uppsala University, BMC, Box 593, 751 24, Uppsala, Sweden
b Department of Neuroscience, Developmental Genetics, Uppsala University, BMC, Box 587, 751 23, Uppsala, Sweden

Author for correspondence: Helgi B. Schiöth, Department of Neuroscience, Biomedical Center, Box 593, 75 124 Uppsala, Sweden, Fax: + 46 18 51 15 40, email; helgi.schioth{at}neuro.uu.se

Received for publication June 24, 2008. Revision received September 2, 2008. Revision received September 24, 2008. Accepted for publication September 27, 2008.

The Adhesion GPCRs are the most complex gene family among GPCRs with large genomic size, multiple introns and a fascinating flora of functional domains, though the evolutionary origin of this family has been obscure. Here we studied the evolution of all class B (7tm2) related genes, including the Adhesion, Secretin and Methuselah families of GPCRs with a focus on nine genomes. We found that the cnidarian genome of Nematostella vectensis has a remarkably rich set of Adhesion GPCRs with a broad repertoire of N-terminal domains while this genome did not have any Secretin GPCRs. Moreover, the single-celled and colony-forming eukaryotes Monosiga brevicollis and Dictyostelium discoideum contain Adhesion-like GPCRs while these genomes do not have any Secretin GPCRs suggesting that the Adhesion type of GPCRs are the most ancient among class B GPCRs. Phylogenetic analysis found Adhesion group V (that contains GPR133 and GPR144) to be the closest relative to the Secretin family in the Adhesion family. Moreover, Adhesion group V sequences in Nematostella vectensis share the same splice site setup as the Secretin GPCRs. Additionally, one of the most conserved motifs in the entire Secretin family is only found in group V of the Adhesion family. We suggest therefore that the Secretin family of GPCRs could have descended from group V Adhesion GPCRs. We found a set of unique Adhesion-like GPCRs in Nematostella vectensis that have long N-termini containing one Somatomedin B domain each, which is a domain configuration similar to that of a set of Adhesion-like GPCRs found in Branchiostoma floridae. These sequences show slight similarities to Methuselah sequences found in insects. The extended class B GPCRs have a very complex evolutionary history with several species-specific expansions and we identified at least 31 unique N-terminal domains originating from other protein classes. The overall N-terminal domain structure, however, concurs with the phylogenetic analysis of the transmembrane (TM) domains, thus enabling us to track the origin of most of the subgroups.

Key Words: evolution • GPCR • G-protein • 7TM • EGF • GRAFS


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