7TM receptors families

Cone cells, like rod cells, contain visual pigments. Like rhodopsin, these photoreceptor proteins are members of the 7TM receptor family and utilize 11-cA-retinal as their chromophore. In human cone cells, there are three distinct photoreceptor proteins with absorption maxima at 426, 530, and 560 nm (Figure 32.26). These absorbances correspond to (in fact, define) the blue, green, and red regions of the spectrum. Recall that the absorption maximum for rhodopsin is 500 nm. 

Odorant receptors are members of the 7TM-receptor family. The green cylinders represent the seven presumed transmembrane helices. Strongly conserved residues characteristic of this protein famiiy are shown in blue, whereas highly variable residues are shown in red. 

The requirement for an oligomeric 7TM receptor for a fully functional response is surprising, considering our previous understanding of 7TM receptors. This discovery has at least two possible explanations. First, the sweet receptor could be a member of a small subset of the 7TM-receptor family that functions well only as oligomers. Alternatively, many 7TM... 

The human oxytocin receptor gene was isolated and characterised in 1994 [122], heralding the development of modern cloned receptor screening. The oxytocin receptor belongs to the Family A series of G-protein coupled 7-transmembrane receptors (GPCRs). A schematic representation of the generic structure of 7TM receptors is shown in Figure 7.3. 

Rhodopsin-Like 7TM Receptors Are the Quantitatively Dominant Family.88... 

Family B Is a Distinct Family of Glucagon/VIP/Caldtonin 7TM Receptors.91... 

FIGURE 2.3 The three main families of mammalian G-protein-coupled 7TM receptors in mammals. No obvious sequence identity is found between the rhodopsin-like family A, the glucagon/VIP/calcitonin family B, and the metabotropic glutamate/chemosensor family C of G-protein-coupled 7TM receptors, with the exception of the disulfide bridge between the top of TM-III and the middle of extracellular loop-2 (see Figure 2.2). Similarly, no apparent sequence identity exists among members of these three families and, for example the 7TM bitter taste receptors, the V1R pheromone receptors, and the 7TM frizzled proteins, which all are either known or believed to be G-protein-coupled receptors. Bacteriorhodopsins, which are not G-protein-coupled proteins but proton pumps, are totally different in respect to amino-acid sequence but have a seven-helical bundle arranged rather similarly to that for the G-protein-coupled receptors. 

RHODOPSIN-LIKE 7TM RECEPTORS ARE THE QUANTITATIVELY DOMINANT FAMILY... 

Much biochemical evidence shows that many if not all 7TM receptors have a strong tendency to aggregate both with themselves and with other 7TM receptors, as most clearly seen in multiple high-molecular-weight bands on sodium dodecyl sulfate (SDS) gels. These bands are by no means restricted to dimers as, in most cases, several higher order oligomeric structures are observed. This is an important point to consider when the functional correlation of dimer formation is addressed in non-family C receptors. 

The GABAb receptor is not a single 7TM receptor but rather a heterodimer formed by two 7TM receptors from family C. The GABAb-R1 receptor, which was initially cloned, binds the ligand GABA, but when expressed alone it is to a large extent retained in the endoplasmic reticulum,... 

The /3-adrenergic receptor is an integral protein with seven hydrophobic regions of 20 to 28 amino acid residues that snake back and forth across the plasma membrane seven times. This protein is a member of a very large family of receptors, all with seven transmembrane helices, that are commonly called serpentine receptors, G protein-coupled receptors (GPCR), or 7 transmembrane segment (7tm) receptors. The binding of epinephrine to a site on the... 

The CaR is a member of family C II of the superfamily of seven transmembrane (7TM) receptors, also termed G protein-coupled receptors (GPCRs) (Brown and MacLeod, 2001). 7TM receptors are by far the largest group of cell surface receptors. They are very important in clinical medicine, since the 7TM receptors represent... 

A Family of 7TM Receptors Almost Certainly Respond to Sweet Compounds... 

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