Multiple regions of G alpha 16 contribute to the specificity of activation by the C5a receptor.
The C5a chemoattractant factor receptor, when expressed in COS-7 cells, can stimulate phosphoinositide-specific phospholipase C activity through the activation of the G16 isoform of the heterotrimeric G protein, but not through the G11 isoform. To identify the regions of the G alpha 16 subunit protein that are responsible for its activation by the C5a receptor, a series of chimeras between G alpha 16 and G alpha 11 were constructed and tested for their ability to be activated by the C5a receptor. Co-transfection experiments with chimeras in which the carboxyl-terminal regions of G alpha 11 were replaced with the corresponding regions of G alpha 16 demonstrated that changes in the carboxyl terminus, e.g., replacement of 134 amino acids, were not sufficient to confer receptor specificity. An additional segment encompassing residues 220-240 of G alpha 16 was required to confer C5a-induced activation. Testing of a reciprocal series of chimeras composed of G alpha 16 sequences at the amino terminus and G alpha 11 sequences at the carboxyl terminus revealed that certain sequences extending from the amino terminus to amino acid 209 of G alpha 16 were sufficient to endow the chimera with much of the specificity for C5a-induced activation. These results suggest that receptor specificity may involve specific conformations of the G protein stabilized by concerted interactions of multiple amino acid sequences distributed throughout the G alpha protein.
Lee
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CH
Division of Biology, California Institute of Technology, Pasadena 91125.
Katz
A
A
Simon
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MI
D000818:Animals; D002460:Cell Line; D015936:Complement C5a / Q000378:metabolism*; D018076:DNA, Complementary; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000502:physiology*; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D044087:Receptor, Anaphylatoxin C5a; D011951:Receptors, Complement / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014162:Transfection
D018076:DNA, Complementary; D044087:Receptor, Anaphylatoxin C5a; D011951:Receptors, Complement; D011993:Recombinant Fusion Proteins; D015936:Complement C5a; D010727:Phosphoric Diester Hydrolases; D019204:GTP-Binding Proteins; D043265:Phosphatidylinositol Diacylglycerol-Lyase