What is a receptor protein?

The intracellular proteins form the most important class of receptors called receptor proteins.
Receptor proteins are located in the cytoplasm, cell membrane, or nuclear membrane.

1. Cytoplasmic receptor proteins include those that respond to steroid hormones. Ligand activated receptors may enter the cell nucleus where they modulate gene expression.

2. Receptors within cell membranes may be peripheral or trans-membrane proteins. Many receptors for hormones and neurotransmission are trans-membrane proteins.

- a. Metabotropic receptors are coupled to G-proteins, acting through various secondary pathways involving ion channels, enzymes such as adenylyl (adenylate) cyclases, and phospholipases, or PDZ domains.
- b. Ionotropic receptors are ligand-activated ion channels that permit entry of ions when the central pore is open. A receptor protein is protein molecule that found embedded in the plasma membrane surface of a cell. It receives chemical signals from outside the cell.