title: Conservation of regulatory function in calcium-binding proteins: human frequenin (neuronal calcium sensor-1) associates productively with yeast phosphatidylinositol 4-kinase isoform, Pik1.
abstract: Frequenin, also known as neuronal calcium sensor-1 (NCS-1), is an N-myristoylated Ca2+-binding protein that has been conserved in both sequence and three-dimensional fold during evolution. We demonstrate using both genetic and biochemical approaches that the observed structural conservation between Saccharomyces cerevisiae frequenin (Frq1) and human NCS-1 is also reflected at the functional level. In yeast, the sole essential target of Frq1 is the phosphatidylinositol 4-kinase isoform, Pik1; both FRQ1 and PIK1 are indispensable for cell viability. Expression of human NCS-1 in yeast, but not a close relative (human KChIP2), rescues the inviability of frq1 cells. Furthermore, in vitro, Frq1 and NCS-1 (either N-myristoylated or unmyristoylated) compete for binding to a small 28-residue motif near the N terminus of Pik1. Site-directed mutagenesis indicates that the binding determinant in Pik1 is a hydrophobic alpha-helix and that frequenins bind to one side of this alpha-helix. We propose, therefore, that the function of NCS-1 in mammals may closely resemble that of Frq1 in S. cerevisiae and, hence, that frequenins in general may serve as regulators of certain isoforms of phosphatidylinositol 4-kinase.
mesh_terms: D019870:1-Phosphatidylinositol 4-Kinase / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism* / Q000502:physiology*; D006801:Humans; D016297:Mutagenesis, Site-Directed; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D051580:Neuronal Calcium-Sensor Proteins; D009479:Neuropeptides; D011485:Protein Binding; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
chemical_list: D002135:Calcium-Binding Proteins; D009419:Nerve Tissue Proteins; D051580:Neuronal Calcium-Sensor Proteins; D009479:Neuropeptides; D029701:Saccharomyces cerevisiae Proteins; C101464:frequenin calcium sensor proteins; D019870:1-Phosphatidylinositol 4-Kinase; C441760:PIK1 protein, S cerevisiae