GPCR oligomerization redux
Many receptors form functional dimers or higher order oligomers on the cell surface. A number of reports have also shown with various levels of certainty that G protein-coupled receptors (GPCRs) di- or oligomerize. In December 2006 we published an Article by Simon Davis and colleagues that challenged how bioluminescence resonance energy transfer (BRET) was being used to investigate GPCR dimerization. In particular, conclusions about ß-adrenergic receptor (ß-AR) dimerization were challenged. The paper was accompanied by a News and Views article by Martin Lohse.
This controversial paper was quickly followed by Correspondences by Michel Bouvier and colleagues and Salahpour and colleagues arguing against the findings. The controversy also seemed to attract a number of papers describing alternative methodologies for examining receptor oligomerization, including time-resolved FRET and snap-tag technologies (Maurel et al., 2008) and sequential BRET–FRET (Carriba et al., 2008).
Fast forward to this week and we see the return of Martin Lohse in a paper where he, Moritz Bunemann and colleagues describe a dual-color fluorescence recovery after photobleaching (FRAP) microscopy approach relying on antibody-mediated receptor immobilization to analyze receptor oligomerization. They focus on ß-AR oligomerization (the subject of controversy in the original papers) and show that ß1-AR shows transient interactions while ß2-AR can form stable oligomers.
What does this mean for the conclusions of the original study? That is difficult to say. FRAP can’t distinguish between direct and indirect interactions so it is even less suitable than BRET for determining the type of interaction that is occuring, but it can distinguish between association of two vs many receptors.
It does appear that the Davis paper highlighted the need for the community to be more conscientious in providing experimental controls using constitutive interacting and non-interacting receptors. This is certainly a positive result and the tools now seem to be in place that will help researchers settle these questions.