Ternary complex, formation agonists

The resulting modification is called the extended ternary complex model [3], which describes the spontaneous formation of active state receptor ([Ra]) from an inactive state receptor ([RJ) according to an allosteric constant (L = [Ra]/[RJ). The active state receptor can form a complex with G-protein ([G]) spontaneously to form RaG, or agonist activation can induce formation of a ternary complex ARaG ... 

Agonists can produce complex binding profiles due to the formation of different protein species (i.e., ternary complexes with G-proteins). The extent of this phenomenon is related to the magnitude of agonist efficacy and can be used to quantify efficacy. 

Ternary complex (model), this model describes the formation of a complex among a ligand (usually an agonist), a receptor, and a G-protein. Originally described by De Lean and colleagues (J. Biol. Chem. 255, 7108-7117, 1980), it has been modified to include other receptor behaviors (see Chapters 3.8 to 3.11), such as constitutive receptor activity. 

The binding of an agonist to a receptor promotes the formation of a ternary LRG complex and an exchange of guanosine-5 -triphosphate (GTP) for guanosine-5 -diphosphate (GDP) on the G protein. The ternary complex is thus activated, promoting dissociation of LR from G and G into its subunits G and... 

Fig. 5. Conceptual schematic of the receptor conformational states elicited by binding to partial (L, ) or full (Ly) agonists, and a depiction of the correlation between the various conformational states and their ability to bind with G proteins. Solid lines show the conformational distributions hypothesized from soluble ternary complex data analyzed by the simple ternary complex model. When a partial agonist binds with a receptor (L R) in this model, the receptor forms a conformational state which has an intermediate affinity for G protein, consequendy leading to formation of intermediate amounts of L RG. On the other hand, the dotted line represents the potential receptor conformations induced by a partial agonist consistent with the extended ternary complex model, which includes the isomerization of receptor between R and R, the only receptor conformation allowed to bind with G protein. For this model, the interactions of a partial agonist with a receptor would result in two populations of ligand-bound receptors with only one (LR ) able to bind with G protein. The x-axis is analogous to the cooperativity factor a.

Agonists bind with higher affinity to the ternary complex than to the binary complex and in addition, stabilize and promote the formation of the ternary complex. The coexistence of these binary and ternary complexes in the membrane provide a molecular basis for the characteristic biphasic, shallow curve of agonist... 

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