Protein–ligand complex

[3][8] Affinity is influenced also by the properties of the solution, like pH, temperature and salt concentration, that may affect the stable state of the proteins and ligands and hence also their interaction and by the presence of other macromolecules that causes macromolecular crowding.

They may have various functions within the cell: catalysis of chemical reactions (enzyme-substrate), defense of the organism through the immune system (antibodies antigen complexes), signal transduction (receptor-ligand complexes) that consists of a transmembrane receptor that upon binding the ligand activates an intracellular cascade.

Lipophilic hormonal receptor complexes can pass the nuclear membrane where transcription may be regulated.

Glucagon binding to GPCRcauses a conformational change in the intracellular domain, allowing interaction with the heterotrimeric Gs protein.

The alpha Subunit of the Gs protein releases bound GDP and binds GTP.

The alpha subunit-GTP complex dissociates from the beta and gamma dimer and interacts with adenylate cyclase.

Binding of glucagon molecule activates many of the alpha subunit, which amplifies the hormonal signal.

The alpha subunit deactivates itself within minutes by hydrolyzing GTP to GDP (GTPase activity).

A better understanding of the protein-ligand complex mechanisms may allow us for the treatment of some diseases such as type 2 diabetes.

Crystal structure of W741L mutant androgen receptor ligand-binding domain and ( R )-bicalutamide complex. [ 1 ] An example of a protein–ligand complex.
These are examples of membrane receptors . Typically, they are proteins that are embedded in the membrane. Although there are many different ligands located outside of the cell, membrane proteins are specific, and only certain ligands will bind to each one. That is why each protein has a different ligand, and also induces a different cellular response. The response may be transcription of a gene, cell growth, or many other cellular actions.