title: High affinity calmodulin target sequence in the signalling molecule PI 3-kinase.
abstract: In this study we report that phosphatidylinositol 3-kinase (PI 3-kinase), a lipid kinase which participates in downstream signalling events of heterotrimeric G protein-coupled receptors and receptor tyrosine kinases, contains a high affinity binding site for calmodulin (CaM). The putative CaM-binding peptide derived from the p110gamma isoform interacts with CaM in a calcium-dependent way. Using gel shift analysis and fluorescence spectrophotometry we discovered that the peptide forms a high affinity complex with CaM. Titration experiments using dansylated CaM gave an affinity constant of 5 nM. Furthermore, a sequence comparison among different PI 3-kinase isoforms revealed that the sequence which can bind CaM is highly conserved within different PI 3-kinase isoforms. These results indicate a novel mechanism for regulating PI 3-kinase and provide a new direct link between Ca2+ and phospholipid signalling pathways.
authors.affiliation: Institute of Molecular Cell Biology, University of Copenhagen, Denmark.
authors.forename: R
authors.initials: R
authors.lastname: Fischer
authors.forename: J
authors.initials: J
authors.lastname: Julsgart
authors.forename: M W
authors.initials: MW
authors.lastname: Berchtold
mesh_terms: D000595:Amino Acid Sequence; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism*; D008969:Molecular Sequence Data; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D013379:Substrate Specificity
chemical_list: D002147:Calmodulin; D019869:Phosphatidylinositol 3-Kinases; D002118:Calcium