Structural and Mechanistic Homology Among GPCRs

In addition, rhodopsin is the only GPCR for which high-resolution crystal structures are available (Li et al., 2004 Okada et al., 2000, 2002, 2004  

Palczewski et al., 2000 Teller et al., 2001), with a maximum resolution of 2.2 A (Okada et al., 2004). While the structures determined by cryoelec-tron microscopy of 2-D crystals (Krebs et al., 2003 Ruprecht et al., 2004 Schertler et al., 1993) are of lower resolution (up to 5.5 A), they provide additional information about the orientation of TM segments relative to the lipid bilayer that cannot be obtained from 3-D crystals. 

There is a growing body of evidence that GPCRs exist as dimers (or oligomers) and that these dimers may be important for G protein activation for at least some GPCR families. This topic has been addressed in 

G protein. Thus, a full agonist maximally activates the cognate G protein while an inverse agonists maximally inhibits any basal activation of the G protein by the receptor. 

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