Die Funktion der Helix 8 für die Regulation des Bradykinin B2 Rezeptors

Upon activation the human bradykinin B2 receptor (B2R) acts as
guanine nucleotide exchange factor for the G proteins Gq/11 and Gi.
Thereafter, it gets phosphorylated by G protein-coupled receptor
kinases (GRKs) and recruits beta-arrestins, which block further G
protein activation and promote B2R 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 B2R. We show here that disruption of helix 8
in the B2R by either C-terminal truncation or just by mutation of a
central amino acid (Lys-315) to a helix-breaking proline resulted
in strong reduction of surface expression. Interestingly, this
malfunction could be overcome by the addition of the
membrane-permeable B2R 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
B2R with GRK2/3 and beta-arrestin2 as shown by
co-immunoprecipitation. Recruitment of beta-arrestin1, however,
required the presence of the C terminus. Taken together, our
results demonstrate that helix 8 of the B2R 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 B2R
with GRK2/3 and beta-arrestins. Additional data obtained with
chimera of B2R with other G protein-coupled receptors of family A
suggest that helix 8 might have similar functions in other GPCRs as
well.