Key cellular receptors can change their shapes, which might allow them to expand the variety of messages they send to cells.
G-protein-coupled receptors (GPCRs) are protein complexes on cell surfaces, where they pick up chemical and protein signals. After receiving a signal, the receptor releases a messenger called a G protein into the cell. G proteins then direct the cell to make a molecule, for instance, or to carry out a metabolic process.
The human genome encodes more than 800 GPCRs, but only a few dozen G proteins. This has led researchers to wonder how a receptor translates an incoming signal into a specific message conveyed by a particular G protein.
Xiangyu Liu at Tsinghua University in Beijing, Brian Kobilka at Stanford University in California and their colleagues crystallized the beta-adrenergic GPCR, which binds adrenaline molecules outside of the cell. The team found that, after binding adrenaline, the receptor can shift its shape into one of two different forms. Each of these forms holds the G protein in a different position.
The researchers suspect that there are other forms of the receptor to ensure that it activates the correct G protein.