Cys-loop receptor superfamily

The insect GABA receptor-chloride ionophore complex is found in the CNS and also at peripheral neuromuscular sites. GABA receptors belong to a superfamily of ligand-gated ion channels known as Cys-loop receptors that include nicotinic acetylcholine receptors and glutamate-gated chloride channels (Lester, 2004). Cys-loop receptors are so named because... 

Fig. 1 Structures of subunits (top) and subunit oligomerization (bottom) in ligand-gated ion channels. (a) P2X receptor family, (b) Ionotropic glutamate receptor family, (c) TRPV channel family, (d) Cys-loop superfamily comprising nAChRs, 5-HT3,GABAa, and glycine receptors.

The cys-loop superfamily, also know as pentameric fast ligand-gated receptors, consists of two subgroups ... 

Figure 16.9 Cartoon illustrating the hypothetical transmembrane topology (left side) and subunit stoichiometry (right side) of the three basic ligand-gated channel superfamilies (1) cys-loop channels (2) glutamate receptor channels and (3) ATP-gated/P2X purinergic receptor channels. The numbers above the arrows refer to the number of subunits that make up the channel pore. The hypothetical ligand-binding sides are indicated in red.

Fig. 2 Seven transmembrane spanning model of the a typical G-protein coupled receptor showing functional domains. The core of about 175 amino acid residues that forms the transmembrane domains (defined by hydropho-bicity analysis) are highly conserved among superfamily members. The extra- and intracellular loop regions and C-terminus are much more divergent, even among closely related receptors. Sites for glycosylation are found on the amino terminus and a palmito-lylation of a Cys in the C-terminal domain are shown. Intracellular residues involved in G-protein coupling and interaction with receptor-specific kinases that mediate desensitization occur on the intracellular loops.

---