A unique fold of phospholipase C-beta mediates dimerization and interaction with G alpha q.
GTP-bound subunits of the Gq family of G alpha subunits directly activate phospholipase C-beta (PLC-beta) isozymes to produce the second messengers inositol 1,4,5-trisphosphate and diacylglycerol. PLC-betas are GTPase activating proteins (GAPs) that also promote the formation of GDP-bound, inactive G beta subunits. Both phospholipase activation by G alpha-GTP subunits and GAP activity require a C-terminal region unique to PLC-beta isozymes. The crystal structure of the C-terminal region from an avian PLC-beta, determined at 2.4 A resolution, reveals a novel fold composed almost entirely of three long helices forming a coiled-coil that dimerizes along its long axis in an antiparallel orientation. The dimer interface is extensive ( approximately 3,200 A(2)), and, based on gel exclusion chromatography, full length PLC-betas are dimeric, indicating that PLC-betas likely function as dimers. Sequence conservation, mutational data and molecular modeling show that an electrostatically positive surface of the dimer contains the major determinants for binding G beta q. Effector dimerization, as highlighted by PLC-betas, provides a viable mechanism for regulating signaling cascades linked to heterotrimeric G proteins.
Singer
Alex U
AU
Department of Pharmacology, The University of North Carolina at Chapel Hill, North Carolina 27599, USA.
Waldo
Gary L
GL
Harden
T Kendall
TK
Sondek
John
J
D000595:Amino Acid Sequence; D000818:Animals; D018360:Crystallography, X-Ray; D019281:Dimerization; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D020962:Heterotrimeric GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D007527:Isoenzymes / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008970:Molecular Weight; D054799:Phospholipase C beta; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D055672:Static Electricity; D014422:Turkeys; D010738:Type C Phospholipases / Q000737:chemistry* / Q000378:metabolism*
D007527:Isoenzymes; D010738:Type C Phospholipases; D054799:Phospholipase C beta; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D020962:Heterotrimeric GTP-Binding Proteins