Ligand-receptor interactions cellular responses

Drug-receptor interactions may quantitatively differ among rapidly converting multiple receptor states that are induced by agonist binding. While most studies commonly focus on analysis of ligand-receptor interactions and cellular responses under presumed steady-state conditions, experimental techniques available for the quantitative analysis of drug-receptor interactions with transient receptor conformational... 

Fig. 3.1 Schematic representation of the series of biochemical steps leading from ligand-receptor interaction to the cellular and physiological responses. LI, L2 and D stand for ligand and drug, respectively. R1 and R2 represent specific membrane receptors that recognize Li and L2. El — n are effector proteins, generally enzymes, modulated by receptor activation or by drugs acting as inhibitors. S is a specific substrate.

The regulation of cell function by extrinsic factors occurs through a series of second-messenger signals that are initiated by ligand-receptor interaction and are responsible from the modulation of both the intensity and the nature of cellular responses. In this manner, second messengers exert control over principal cellular events, such as metabolism, secretion, strucmre, and replication. ... 

Ligand-bound corticosteroid receptors have been shown to interact to form heterodimers with other transcription factors, such as the jun protein. Such interactions are responsible for transactivation of the ds-regulatory sites known as AP-1 sites and for the glucocorticoid-mediated suppression of transcription, such as that seen in the pro-opiomelanocortin gene. A number of such specific protein interactions have been reported these interactions and their locations relative to other transcription factors transform a ubiquitous steroid hormone signal into a tissue-specific, graded cellular response. 

Figure 14-1. Signaling via G protein-coupled receptors. Ligand binding to its cell-surface receptor initiates interaction of the receptor with the heterotrimeric G protein for which it is specific. A conformational change in the G protein brought about by binding of the ligand-receptor complex promotes exchange of GDP for GTP. The activated Gd-GTP dissociates from the Gp complex and both can interact with effectors, which carry on the signal to the mechanism that implements the cellular response.

---