GAP-43 augmentation of G protein-mediated signal transduction is regulated by both phosphorylation and palmitoylation.
The neuronal protein GAP-43 is concentrated at the growth cone membrane, where it is thought to amplify the signal transduction process. As a model for its neuronal effects, GAP-43 protein injection into Xenopus laevis oocytes strongly augments the calcium-sensitive chloride current evoked by the G protein-coupled receptor stimulation. We have now examined a series of GAP-43 mutants in this system and determined those regions of GAP-43 required for this increase in current flux. As expected, palmitoylation inhibits signal amplification in oocytes by blocking G protein activation. Unexpectedly, a second domain of GAP-43 (residues 35-50) containing a protein kinase C phosphorylation site at residue 41 is also necessary for augmentation of G protein-coupled signals in oocytes. This region is not required for activation of isolated Go but is necessary for GAP-43 binding to isolated calmodulin and to isolated protein kinase C. Substitution of Asp for Ser41 inactivates GAP-43 as a signal facilitator in oocytes. This mutation blocks GAP-43 binding to both protein kinase C and calmodulin. Thus, GAP-43 regulates an oocyte signaling cascade via coordinated, simultaneous G protein activation and interaction with either calmodulin or protein kinase C.
Nakamura
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F
Department of Neurology, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
Strittmatter
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P
Strittmatter
S M
SM
D019943:Amino Acid Substitution; D000818:Animals; D001224:Aspartic Acid; D002147:Calmodulin / Q000737:chemistry / Q000378:metabolism; D018118:Chloride Channels / Q000502:physiology; D004594:Electrophysiology; D019922:GAP-43 Protein / Q000235:genetics / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000502:physiology*; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000201:enzymology; D019308:Palmitic Acid / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011985:Receptors, Serotonin / Q000502:physiology; D012694:Serine; D015398:Signal Transduction / Q000502:physiology*; D014982:Xenopus laevis
D002147:Calmodulin; D018118:Chloride Channels; D019922:GAP-43 Protein; D011985:Receptors, Serotonin; D019308:Palmitic Acid; D001224:Aspartic Acid; D012694:Serine; D011493:Protein Kinase C; D019204:GTP-Binding Proteins