Adrenaline-activated structure of the beta 2 adrenoceptor stabilized with an engineered nanobody
 |
Figure: The beta 2 AR (green) bound
to adrenaline (orange) and stabilized in an active state by an engineered
nanobody (blue). |
Brian Kobilka group (Stanford University) and collaborators
The groups of Brian Kobilka, Bill Weis, and Chris Garcia at
Stanford University determined the adrenaline-activated structure of the beta
2 adrenoceptor stabilized with an engineered nanobody. The beta 2 adrenergic
receptor (beta 2 AR) is a G-protein-coupled receptor (GPCR) that mediates
cellular responses to adrenaline. Kobilka, Weis, and collaborators have
previously obtained structures of the beta 2 AR in inactive and active
states, but it had not been possible to capture an active-state of a GPCR
bound to its native neurotransmitter. Crystal structures of agonist-bound
GPCRs have relied on the use of either exceptionally high-affinity agonists
or receptor stabilization by mutagenesis. Many natural agonists such as
adrenaline bind with relatively low affinity, and they are often chemically
unstable. Using directed evolution, they engineered a high-affinity camelid
antibody fragment (nanobody) that stabilizes the active state of the beta 2
AR, and used this to obtain crystal structures of the activated receptor
bound to three chemically distinct agonists: the ultrahigh-affinity agonist
BI167107, the high-affinity catecholamine agonist hydroxybenzyl
isoproterenol, and the low-affinity endogenous agonist adrenaline. The
crystal structures reveal a highly conserved overall ligand recognition and
activation mode despite diverse ligand chemical structures and affinities
that range from 100 nM to ~80 pM. Overall, the adrenaline-bound receptor
structure is similar to the others, but it has substantial rearrangements in
extracellular loop three and the extracellular tip of transmembrane helix 6.
These structures also reveal a water-mediated hydrogen bond between two
conserved tyrosines that appears to stabilize the active state of the beta 2
AR and related GPCRs.
Citation: Ring, AM, Manglik, A, Kruse, AC, Enos, MD, Weis,
WI, Garcia, KC, Kobilka, BK. Adrenaline-activated structure of [beta
subscript 2]-adrenoceptor stabilized by an engineered nanobody, Nature 502,
575-579 (2013). DOI: 10.1038/nature12572
|