PSI Structural Biology Knowledgebase

PSI | Structural Biology Knowledgebase
Header Icons
E-Collection

Related Articles
Families in Gene Neighborhoods
June 2015
Signaling: A Platform for Opposing Functions
May 2015
Nuclear Pore Complex: A Flexible Transporter
February 2015
Nuclear Pore Complex: Higher Resolution of Macromolecules
February 2015
Nuclear Pore Complex: Integrative Approach to Probe Nup133
February 2015
Piecing Together the Nuclear Pore Complex
February 2015
iTRAQing the Ubiquitinome
July 2014
CAAX Endoproteases
August 2013
The Immune System: A Strong Competitor
June 2013
The Immune System: Strand Swapping for T-Cell Inhibition
June 2013
PDZ Domains
April 2013
Protein Interaction Networks: Adding Structure to Protein Networks
April 2013
Protein Interaction Networks: Morph to Assemble
April 2013
Protein Interaction Networks: Reading Between the Lines
April 2013
Protein Interaction Networks: When the Sum Is Greater than the Parts
April 2013
Alpha-Catenin Connections
March 2013
Cytochrome Oxidase
November 2012
Bacterial Phosphotransferase System
October 2012
Solute Channels
September 2012
Budding ensemble
August 2012
The machines behind the spindle assembly checkpoint
June 2012
G Protein-Coupled Receptors
May 2012
Revealing the Nuclear Pore Complex
March 2012
Topping off the proteasome
March 2012
Anchoring's the way
February 2012
Reading out regioselectivity
December 2011
An effective and cooperative dimer
November 2011
PDZ domains: sometimes it takes two
November 2011
Raising a glass to GLIC
August 2011
A2A Adenosine Receptor
May 2011
A growing family
February 2011
FERM-ly bound
February 2011
CXCR4
January 2011
Guard cells pick up the SLAC
December 2010
Zinc Transporter ZntB
July 2010
Zinc Transporter ZntB
July 2010
Importance of extension for integrin
June 2010
Spot protein-protein interactions… fast
March 2010
Alg13 Subunit of N-Acetylglucosamine Transferase
February 2010
Urea transporter
February 2010
Two-component signaling
December 2009
ABA receptor...this time for real?
November 2009
Network coverage
November 2009
Get3 into the groove
October 2009
Guanine Nucleotide Exchange Factor Vav1 and Rho GTPase Rac1
October 2009
GPCR subunits: Separate but not equal
September 2009
Proofreading RNA
July 2009
Ribonuclease and Ribonuclease Inhibitor
April 2009
The elusive helicase
April 2009
Click for cancer-protein interactions
December 2008

Research Themes Protein-protein interactions

GPCR subunits: Separate but not equal

PSI-SGKB [doi:10.1038/fa_psisgkb.2009.39]
Featured Article - September 2009
Short description: A functional complementation assay reveals that maximal heterotrimeric G-protein activation is achieved by agonist binding to one subunit of a dopamine D2 receptor dimer.

Cartoon of different D2R dimer activation states, with activation data for these states, from the perspective of agonist-mediated activation of protomer A.

What is the minimal functional unit of a G protein-coupled receptor (GPCR)? Some receptors have been proposed to exist in a 2:1 stoichiometry with heterotrimeric G proteins, although rhodopsin and the β2 adrenergic receptor can activate G proteins in vitro as monomers. In addition, it is not always clear whether agonists bind one or both subunits of a receptor dimer. Reporting in Nature Chemical Biology, Jonathan Javitch and colleagues use a functional complementation assay to study the stoichiometry of human dopamine D2 receptor (D2R) signaling. They find that a D2R dimer binds to a single heterotrimeric G protein and is maximally activated by the binding of an agonist to one receptor protomer.

To study D2R activation, Han et al. fused one D2R (called protomer B) to a novel pertussis-toxin-insensitive Gqi5 chimera that produced calcium-dependent luminescence upon activation. The fusion protein did not signal in response to agonist binding because the very short linker did not allow the G protein to couple to the receptor to which it was fused. However, co-expression of a D2R protomer not fused to a G protein (called protomer A) caused robust agonist-mediated activation. Therefore, agonist-induced D2R signaling is mediated by two receptor protomers and one G protein.

A mutation in protomer A that inhibited agonist binding blocked G-protein-mediated signaling. Surprisingly, this same mutation in protomer B increased G-protein activation compared to the wild-type homodimer. Inverse agonist binding to protomer B also enhanced activation. Thus, the binding of an agonist to one subunit of a dimer is necessary and sufficient for G-protein activation. Intriguingly, agonist binding to protomer B, as well as a constitutively active version of protomer B, both diminished agonist-induced G-protein activation, suggesting that the active conformation of protomer B inhibits signaling and that agonist binding per se is not required for this effect.

Computational modeling and additional mutagenesis studies suggested that the second intracellular loop of both protomers makes contact with the G protein. However, the third intracellular loop of protomer A but not protomer B is required for G-protein activation, which indicates that each protomer in a receptor dimer has a discrete function. Given the apparent asymmetrical role of these protomers and the importance of conformational changes in modulating G-protein activation, it will be interesting to determine the effects of heterodimerization on agonist-stimulated signaling. The complementation assay described in this report will be a useful technique for these future studies.

Related articles

GPCR modeling: any good?

A pocket guide to GPCRs

Evolving a better-expressing GPCR

Emily Chenette

References

  1. Y. Han et al. Allosteric communication between protomers of dopamine class A GPCR dimers modulates activation.
    Nature Chem. Biol. (2009). doi:10.1038/nchembio.199

Structural Biology Knowledgebase ISSN: 1758-1338
Funded by a grant from the National Institute of General Medical Sciences of the National Institutes of Health