17 Cell membrane receptors and cell signalling
K. WILSON
17.1 Receptors for cell signalling
17.2 Quantitative aspects of receptor–ligand binding
17.3 Ligand-binding and cell-signalling studies
17.4 Mechanisms of signal transduction
17.5 Receptor trafficking
17.6 Suggestions for further reading
17.1 RECEPTORS FOR CELL SIGNALLING
17.1.1 Intercellular signal transduction
Cells in multicellular organisms need to be able to communicate with each other in
order to respond to external stimuli and to coordinate their activities to achieve
homeostasis. Such communication is termedintercellular signallingand is achieved by:
- The release by the ‘signalling’ cells ofsignalling molecules, referred to asendogenous
agonistsorfirst messengers.
- The specific recognition and binding of these agonists byreceptor molecules, simply
referred to as receptors, located either in the cell membrane or in the cytoplasm of the
‘target’ cell. Each cell membrane contains between 10^3 and 10^6 molecules of a given
receptor. Binding of the agonist to a specific binding domain on the receptor changes
the receptor from its inactive,resting state, to an active state. Exceptionally, a
receptor may possess activity in the absence of agonist. Such receptors are said to
possessconstitutive activity.
- The initiation of a sequence of molecular events commonly involving interaction
between the active receptor and other, so-called effector molecules, the whole process
being referred to asintracellular signal transductionwhich terminates in the final
cellular response.
Agonist signalling molecules range from the gas nitric oxide, amines, amino acids,
nucleosides, nucleotides and lipids to hormones, growth factors, interleukins,
660
