CRYSTAL-STRUCTURE OF A G(A) PROTEIN BETA-GAMMA DIMER AT 2.1-ANGSTROM RESOLUTION

MANY signalling cascades use seven-helical transmembrane receptors cou pled to heterotrimeric G proteins (G(alpha beta gamma)) to convert ext racellular signals into intracellular responses(1). Upon nucleotide ex change catalysed by activated receptors, heterotrimers dissociate into GTP-bound G(alpha) subunits and G(beta gamma) dimers, either of which can modulate many downstream effectors(2,3). Here we use multiwavelen gth anomalous diffraction data to solve the crystal structure of the b eta gamma dimer of the G protein transducin. The beta-subunit is prima rily a seven-bladed beta-propeller that is partially encircled by an e xtended gamma-subunit. The beta-propeller, which contains seven struct urally similar WD repeats, defines the stereochemistry of the WD repea t and the probable architecture of all WD-repeat-containing domains. T he structure details interactions between G protein beta- and gamma-su bunits and highlights regions implicated in effector modulation for th e conserved family of G protein beta gamma dimers.