Cell-Surface Receptor

Cell-surface receptors, also known as transmembrane receptors, are cell surface, membrane-anchored (integral) proteins that bind to external ligand molecules. This type of receptor spans the plasma membrane and performs signal transduction, in which an extracellular signal is converted into an intercellular signal. Ligands that interact with cell-surface receptors do not have to enter the cell that they affect.

Each cell-surface receptor has three main components: an external ligand-binding domain, a hydrophobic membrane-spanning region, and an intracellular domain inside the cell. The ligand-binding domain is also called the extracellular domain.

Cell-surface receptors are involved in most of the signaling in multicellular organisms. There are three general categories of cell-surface receptors: ion channel-linked receptors, G-protein-linked receptors (GPCRs), and enzyme-coupled receptors (Figure 1). One example of this type of enzyme-linked is the receptor tyrosine kinase (RTK) family of proteins.

Three types of receptors are embedded inside the plasma membrane, indicated by thick grey, horizontal line. First receptor - GPCR - is represented by a long dark green string, which passes through the membrane 7 times, with each loop sticking out of the membrane on either side of it. Between the fifth and sixth loop, a small red sphere is attached on the outer side of the membrane, named signal molecule. On the opposite side of this place, the receptor loop emits signals indicated by multiple red vertical stripes. Second receptor - enzyme-linked - presents two light grey, identical, thin, vertical structures with both ends sticking out of the membrane on each side. The upper parts create a small horizontal platform, where red and pink short structures are attached, named signal molecules. On the lower part, to each of the two green vertical structures, three yellow spheres with letter P inside are attached.The last receptor - named channel - presents two yellow, identical structures with the upper part sticking out of the membrane. To each side of the two yellow structures, a small blue sphere is attached, named signal molecule. In between the two structures, a black arrow pointing downwards passes by, indicating the flow of ions through the channel to the inside of the cell.

Figure 1: Three types of cell-surface receptors: G-protein-linked receptors (GPCRs), enzyme-coupled receptors, ion channel-linked receptors.

Acknowledgement The content of these theory pages has been developed based on the resources provided by: OpenStax College, Biology. (OpenStax CNX. Mar 13, 2015)