Heterotrimeric G protein complex molecule. Computer model showing the secondary structure of a heterotrimeric G protein complex. Alpha-helices are red and beta sheets are yellow. This protein has three different subunits (heterotrimer), alpha, beta and gamma. G proteins, or guanine nucleotide binding proteins, are molecular switches involved in signal transduction. Heterotrimeric G proteins relay signals from cell surface receptors to their effectors, including ion channels and enzymes, within a cell.