Involvement of the Amino Terminus of the B2 Receptor in Agonist-induced Receptor Dimerization

Abstract

The mechanisms and the functional importance of G-protein-coupled receptor dimerization are poorly understood. We therefore analyzed dimerization of the bradykinin B 2 receptor. The binding of the agonist bradykinin to the B 2 receptor endogenously expressed on PC-12 cells led to the formation of receptor dimers, whereas the B 2 antagonist HOE140 did not induce dimerization, suggesting that B 2 receptor dimerization was linked to receptor activation. Addition of a peptide corresponding to the amino terminus of the receptor reduced the amount of detected B 2 receptor dimers, whereas peptides derived from the extracellular loops had The mechanism and the function of agonist-induced receptor dimerization of G-protein-coupled receptors is still a matter of debate. For a variety of G-protein-coupled receptors, receptor dimers have been detected recently, e.g. for the ␤ 2 -adrenergic receptor (1), the dopamine D 2 receptor (2), the metabotropic glutamate receptor 5 (3), or the calcium sensing receptor (4). G-protein-coupled receptors seem to dimerize via two different mechanisms. Whereas dimerization of the dopamine D 2 and the ␤ 2 -adrenergic receptor occurs via transmembrane regions, the metabotropic glutamate receptor and the calcium sensing receptor dimerize via their large amino terminus and, to a lesser extent, via their transmembrane regions (1-4). G-protein-coupled receptors are classified into three main families according to the structure and length of their amino terminus and the localization of the agonist binding site (5). The metabotropic glutamate receptor and the calcium sensing receptor are members of family 3 receptors. In family 3 receptors, the amino terminus is not only involved in dimerization but also essential for agonist binding. In contrast, adrenaline and dopamine, which are agonists on family 1 receptors, bind within the seven transmembrane helices (5). The transmembrane regions are also involved in dimerization of these receptors (1, 2). Thus, the mechanism of receptor dimerization seems to be related to agonist binding. To further investigate this hypothesis, we analyzed dimerization of the bradykinin B 2 receptor. The B 2 receptor belongs also to family 1. However, receptors for catecholamines or dopamine belong to the 1a subfamily, whereas receptors for peptides like bradykinin are classified into the subfamily 1b (5). In contrast to family 1a receptors, 1b-type receptors are characterized by an agonist binding site within the amino terminus of the receptor and the extracellular loops (5). In accordance with its classification as a family 1b receptor, a binding site(s) for the agonist bradykinin was identified within the extracellular loop regions, e.g. the connecting loops between membrane domains IV and V and domains VI and VII (6 -9). Because the agonist binding site of 1b receptors differs from that of 1a family receptors, we asked whether the sites necessary for receptor dimerization were also different between members of these two subfamilies. Here, we report that binding of brady...

Paradoxical Block of Parathormone Secretion Is Mediated by Increased Activity of Gα Subunits

“…The codon coding for arginine 209 of G␣ i1 was exchanged to cysteine by site-directed mutagenesis (16). For mutagenesis of the human CaSR, an additional restriction site for XhoI was introduced (silent mutation of leucine 276).…”

“…Cell Culture and Transfection-Human embryonic kidney cells (HEK-293) were cultivated and transfected with plasmids encoding the wild-type and the different CaSR mutants (7,(13)(14)(15) under the control of the cytomegalovirus promotor as described (16).…”

Spontaneous Formation of a Proteolytic B1 and B2 Bradykinin Receptor Complex with Enhanced Signaling Capacity

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The Kallikrein-Kinin System as a Regulator of Cardiovascular and Renal Function

“…Blockade or deletion of B 1 or B 2 has been found to have a protective effect in experimental models of inflammation, including (1) bacterial infections (118), (2) parasites (246), (3) lipopolysaccharide-induced acute renal inflammation (17), (4) capsaicin-induced skin inflammation, which required deletion of both B 1 and B 2 (209), (5) streptozotocin-induced diabetes, wherein insulitis was reportedly mediated by B 1 and proteinuria by B 2 (322), (6) periodontitis induced by Gram-negative bacteria, mediated via cross-talk between Toll-like receptor type 2 (TLR2) and B 2 which resulted in the development of either IFN-γ-or IL-17-producing T cells (175), (7) 2,4,6-trinitrobenzene sulfonic acid-induced inflammatory bowel disease, mediated via B 1 (99), (8) experimental arthritis (63,263), and human rheumatoid and osteoid arthritis (54,166) (Fig. 3).…”

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