Characterisation of AmphiAmR11, an Amphioxus (Branchiostoma floridae) D2-Dopamine-Like G Protein-Coupled Receptor

Asha L. Bayliss,Peter D. Evans,Wolfgang Blenau

doi:10.1371/journal.pone.0080833

Abstract

The evolution of the biogenic amine signalling system in vertebrates is unclear. However, insights can be obtained from studying the structures and signalling properties of biogenic amine receptors from the protochordate, amphioxus, which is an invertebrate species that exists at the base of the chordate lineage. Here we describe the signalling properties of AmphiAmR11, an amphioxus (Branchiostoma floridae) G protein-coupled receptor which has structural similarities to vertebrate α2-adrenergic receptors but which functionally acts as a D2 dopamine-like receptor when expressed in Chinese hamster ovary -K1 cells. AmphiAmR11 inhibits forskolin-stimulated cyclic AMP levels with tyramine, phenylethylamine and dopamine being the most potent agonists. AmphiAmR11 also increases mitogen-activated protein kinase activity and calcium mobilisation, and in both pathways, dopamine was found to be more potent than tyramine. Thus, differences in the relative effectiveness of various agonists in the different second messenger assay systems suggest that the receptor displays agonist-specific coupling (biased agonism) whereby different agonists stabilize different conformations of the receptor which lead to the enhancement of one signalling pathway over another. The present study provides insights into the evolution of α2-adrenergic receptor signalling and support the hypothesis that α2-adrenergic receptors evolved from D2-dopamine receptors. The AmphiAmR11 receptor may represent a transition state between D2-dopamine receptors and α2-adrenergic receptors.

Highlights

Studying the complement of biogenic amine receptors in the cephalochordate, amphioxus, can provide insight into the evolution of the biogenic amine signalling system present in vertebrates
Histamine at 1 μM had no effect on forskolin-stimulated cAMP levels in AmphiAmR11-expressing Chinese hamster ovary (CHO)-K1 cells (Figure S1A in File S1)
Control experiments showed that the biogenic amines used on AmphiAmR11-expressing CHO-K1 cells had no significant effect on forskolin-stimulated cAMP levels in wild type CHO-K1 cells [10]. 5-HT was not used in the assay since CHO-K1 cells have endogenous 5HT1B receptors [26]

Summary

Introduction

Studying the complement of biogenic amine receptors in the cephalochordate, amphioxus, can provide insight into the evolution of the biogenic amine signalling system present in vertebrates. It is predicted to have 44 biogenic amine receptors [5,6] and expresses high levels of octopamine, dopamine and serotonin, and trace levels of noradrenaline [7]. The characterisation of three of the 44 predicted biogenic amine receptors, AmphiD1/β, AmphiAmR1 and AmphiAmR2, showed that amphioxus has both vertebrate-type and invertebrate-type D1-dopamine receptors [8,9]. The characterisation of one of the five receptors, AmphiAmR4, showed that amphioxus has at least one α2adrenregic-like receptor and implied that an adrenergic signalling system, albeit a simple one, likely exists in amphioxus [10]

Methods

Results

Conclusion