title: Molecular interactions of yeast frequenin (Frq1) with the phosphatidylinositol 4-kinase isoform, Pik1.
abstract: Frq1, a 190-residue N-myristoylated calcium-binding protein, associates tightly with the N terminus of Pik1, a 1066-residue phosphatidylinositol 4-kinase. Deletion analysis of an Frq1-binding fragment, Pik1-(10-192), showed that residues within 80-192 are necessary and sufficient for Frq1 association in vitro. A synthetic peptide (residues 151-199) competed for binding of [(35)S]Pik1-(10-192) to bead-immobilized Frq1, whereas shorter peptides (164-199 and 174-199) did not. Correspondingly, a deletion mutant, Pik1(delta152-191), did not co-immunoprecipitate efficiently with Frq1 and did not support growth at elevated temperature. Site-directed mutagenesis of Pik1-(10-192) suggested that recognition determinants lie over an extended region. Titration calorimetry demonstrated that binding of an 83-residue fragment, Pik1-(110-192), or the 151-199 peptide to Frq1 shows high affinity (K(d) approximately 100 nm) and is largely entropic, consistent with hydrophobic interaction. Stoichiometry of Pik1-(110-192) binding to Frq1 was 1:1, as judged by titration calorimetry, by changes in NMR spectrum and intrinsic tryptophan fluorescence, and by light scattering. In cell extracts, Pik1 and Frq1 exist mainly in a heterodimeric complex, as shown by size exclusion chromatography. Cys-15 in Frq1 is not S-palmitoylated, as assessed by mass spectrometry; a Frq1(C15A) mutant and even a non-myristoylated Frq1(G2A,C15A) double mutant rescued the inviability of frq1Delta cells. This study defines the segment of Pik1 required for high affinity binding of Frq1.
authors.affiliation: Department of Molecular and Cell Biology, Division of Biochemistry and Molecular Biology, University of California, Berkeley, California 94720-3202, USA.
authors.forename: Inken G
authors.initials: IG
authors.lastname: Huttner
authors.forename: Thomas
authors.initials: T
authors.lastname: Strahl
authors.forename: Masanori
authors.initials: M
authors.lastname: Osawa
authors.forename: David S
authors.initials: DS
authors.lastname: King
authors.forename: James B
authors.initials: JB
authors.lastname: Ames
authors.forename: Jeremy
authors.initials: J
authors.lastname: Thorner
mesh_terms: D019870:1-Phosphatidylinositol 4-Kinase / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D013058:Mass Spectrometry; D011485:Protein Binding; D011487:Protein Conformation; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism*; D017384:Sequence Deletion; D013329:Structure-Activity Relationship
chemical_list: D002135:Calcium-Binding Proteins; C400903:FRQ1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D019870:1-Phosphatidylinositol 4-Kinase; C441760:PIK1 protein, S cerevisiae