The conformational switch in 7-transmembrane receptors: the muscarinic receptor paradigm

The rhodopsin-like superfamily of 7-transmembrane receptors is the largest class of signalling molecules in the mammalian genome. Recently, a combinat ion of mutagenesis, biophysical and modelling studies have suggested a cred ible model for the alpha-carbon backbone in the transmembrane region of the 7-transmembrane receptors, and have started to reveal the structural basis of the conformational switch from the inactive to the active state. A key feature may be the replacement of a network of radial constraints, centred an transmembrane helix three, which stabilise the inactive ground state of the receptor by a new set of axial interactions which help to stabilise the activated state. Transmembrane helix three may act as a rotary switch in t he activation mechanism. (C) 1999 Elsevier Science B.V. All rights reserved .