Molecular interactions of yeast frequenin (Frq1) with the phosphatidylinositol 4-kinase isoform, Pik1

Inken G. Huttner, Thomas Strahl, Masanori Osawa, David S. King, James B. Ames, Jeremy Thorner

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38 Citations (Scopus)


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 [35S]Pik1-(10-192) to bead-immobilized Frq1, whereas shorter peptides (164-199 and 174-199) did not. Correspondingly, a deletion mutant, Pik1(Δ152-191), 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 (Kd ∼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 frq1Δ cells. This study defines the segment of Pik1 required for high affinity binding of Frq1.

Original languageEnglish
Pages (from-to)4862-4874
Number of pages13
JournalJournal of Biological Chemistry
Issue number7
Publication statusPublished - 2003 Feb 14
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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