Helix 8 Plays a Crucial Role in Bradykinin B2 Receptor Trafficking and Signaling

Abstract

Upon activation the human bradykinin B 2 receptor (B 2 R) acts as guanine nucleotide exchange factor for the G proteins G q/11 and G i . Thereafter, it gets phosphorylated by G protein-coupled receptor kinases (GRKs) and recruits ␤-arrestins, which block further G protein activation and promote B 2 R internalization via clathrin-coated pits. As for most G protein-coupled receptors of family A, an intracellular helix 8 after transmembrane domain 7 is also predicted for the B 2 R. We show here that disruption of helix 8 in the B 2 R by either C-terminal truncation or just by mutation of a central amino acid (Lys-315) to a helixbreaking proline resulted in strong reduction of surface expression. Interestingly, this malfunction could be overcome by the addition of the membrane-permeable B 2 R antagonist JSM10292, suggesting that helix 8 has a general role for conformational stabilization that can be accounted for by an appropriate antagonist. Intriguingly, an intact helix 8, but not the C terminus with its phosphorylation sites, was indispensable for receptor sequestration and for interaction of the B 2 R with GRK2/3 and ␤-arrestin2 as shown by co-immunoprecipitation. Recruitment of ␤-arrestin1, however, required the presence of the C terminus. Taken together, our results demonstrate that helix 8 of the B 2 R plays a crucial role not only in efficient trafficking to the plasma membrane or the activation of G proteins but also for the interaction of the B 2 R with GRK2/3 and ␤-arrestins. Additional data obtained with chimera of B 2 R with other G protein-coupled receptors of family A suggest that helix 8 might have similar functions in other GPCRs as well.The human bradykinin B 2 receptor (B 2 R) 2 belongs to the family A (rhodopsin/␤-adrenergic-like) of G protein-coupled receptors (GPCRs). The B 2 R is ubiquitously expressed in many cells and tissues, and its activation results in a variety of physiological effects that range from vasodilatation and increased vascular permeability to hyperalgesia and natriuresis (1). Recent studies with B 2 R knock-out mice also point to a protective role of the B 2 R in the process of aging and in diabetes (2). After extracellular binding of its endogenous agonists, of the nona-peptide bradykinin (BK), or of kallidin (Lys-BK), the B 2 R undergoes conformational changes that turn it into a guanine nucleotide exchange factor for the G proteins G q/11 and G i , thus leading to the activation of G protein-dependent signaling cascades. Among other events, this results in phosphatidylinositol hydrolysis and activation of MAPK pathways. As reported for many GPCRs, desensitization of the B 2 R comes along with phosphorylation of serine/threonine residues in its C terminus by G protein-coupled receptor kinases (GRKs) or second messenger kinases as well as recruitment of ␤-arrestins and ends with the sequestration of the receptor into intracellular compartments (1). Upon short term stimulation the receptor gets recycled to the plasma membrane, whereas long term stimulation leads to the down-...

Novel Screening Assay for the Selective Detection of G-Protein-Coupled Receptor Heteromer Signaling

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Identification of a binding element for the cytoplasmic regulator FROUNT in the membrane-proximal C-terminal region of chemokine receptors CCR2 and CCR5

“…Our studies demonstrated that the helical state of the helix 8 region is responsible for binding to the cytoplasmic protein FNT ( Figure 4); furthermore, residues on the hydrophobic side of the helix 8 region are completely conserved among the two FNT-binding receptors CCR2 and CCR5 ( Figure 5). Previous reports have demonstrated important roles for the helix 8 region in receptor activation [26][27][28], although the molecular mechanisms remain unclear. The results of the present study provide new insight into the regulation mechanism mediated by helix 8, in which the hydrophobic side of helix 8 serves as a binding site for a cytoplasmic regulator.…”

International Union of Basic and Clinical Pharmacology. LXXXVII. Complement Peptide C5a, C4a, and C3a Receptors

“…It is not known if this Cys 516 is actually modified in vivo. A potential eighth helix at the C terminus (Asn431-Gln451) is suggested by sequence similarities to bradykinin R2 and other receptors (Feierler et al, 2011). Interestingly, the C5a 1 and C5a 2 receptors do not have this basic sequence and also contain proline, a potential helix blocker.…”