Molecular Interactions of Yeast Frequenin (Frq1) with the Phosphatidylinositol 4-Kinase Isoform, Pik1

Abstract

Recognition that phosphoinositides and inositol phosphates are key regulators of many processes in eukaryotic cells has brought increased attention to the enzymes that regulate the synthesis and turnover of these molecules (reviewed in Refs. 1-3). Of particular interest are the enzymes responsible for producing the various polyphosphoinositides situated on the cytosolic face of cellular membranes, which initiate several different signaling pathways by serving as highly specific recognition determinants for the selective recruitment of proteins to membranes (reviewed in Refs. 4 -7) and as the precursors for several intracellular second messengers (reviewed in Refs. 8 -10). The first committed step in the synthesis of the polyphosphoinositide, phosphatidylinositol 4,5-bisphosphate, is considered to be ATP-dependent phosphorylation of the hydrophilic myo-inositol head group of phosphatidylinositol (PtdIns) 1 at the D-4 position by PtdIns 4-kinase (ATP:1-phosphatidyl-1D-myo-inositol 4-phosphotransferase, EC 2.7.1.67) (reviewed in Refs. 11-13) . The resulting product, PtdIns(4)P, can be phosphorylated on the D-5 position by PtdIns(4)P 5-kinase to generate PtdIns(4,5)P 2 , PtdIns(4,5)P 2 can be phosphorylated on the D-3 position by yet other lipid kinases, and the phosphoinositides so generated can be converted to other species by specific phosphatases and phospholipases (reviewed in Refs. 14 -17).The first PtdIns 4-kinase to be purified to homogeneity from any organism (18), and to have the corresponding gene cloned (19,20), was Pik1 from the yeast Saccharomyces cerevisiae. Thereafter, a second isoform, Stt4, which is the product of a discrete gene, was described (21). Absence of either Pik1 or Stt4 is lethal, and overproduction of each protein cannot compensate for absence of the other, indicating that these enzymes participate in distinct cellular processes and generate discrete pools of PtdIns(4)P that are essential for yeast cell viability. Indeed, subsequent work has shown that, together, Pik1 and Stt4 account for all of the PtdIns(4)P generated in the yeast cell (22) and that Pik1 is required for vesicular trafficking in the late secretory pathway (23, 24) and perhaps for cytokinesis (20), whereas Stt4 plays roles in cell wall integrity, maintenance of vacuole morphology, and aminophospholipid transport from the endoplasmic reticulum to the Golgi (25-27). The presence of Pik1-and Stt4-like isoforms is also conserved in metazoans (11,12,28).We have shown previously that Frq1, a small calcium-bind-

Interaction of Neuronal Calcium Sensor-1 and ADP-ribosylation Factor 1 Allows Bidirectional Control of Phosphatidylinositol 4-Kinase β and trans-Golgi Network-Plasma Membrane Traffic

“…The NCS-1 used for our experiments was not myristoylated, and the previous study suggested that myristoylation was required. It should be noted that the homologous interaction between yeast proteins is not dependent on myristoylation of Frq1 (49). Although a genetic interaction between ARF and Pik1 has been inferred in yeast (8) mammalian ARF1 has been demonstrated to recruit a PI(4)K␤ activity to isolated Golgi membranes (6) and to increase activity of PI(4)K␤ (50), no evidence for a direct physical interaction between the two proteins has thus far been provided.…”

Recoverin Binds Exclusively to an Amphipathic Peptide at the N Terminus of Rhodopsin Kinase, Inhibiting Rhodopsin Phosphorylation without Affecting Catalytic Activity of the Kinase

“…In addition, frequentin is an neuronal calcium sensor protein that binds to the phosphatidylinositol 4-kinase isoform, Pik1. In this case, hydrophobic residues within a 28-residue peptide from Pik1 (residues 145-172) form an amphipathic helical binding site for frequentin (39,40).…”

Phosphoinositides: Tiny Lipids With Giant Impact on Cell Regulation

“…ts strains show greatly distorted and exaggerated Golgi membranes, vacuole fragmentation, and defective actin polarization at the budding pole (64,1655 (672). The Golgi recruitment of Pik1p is also controlled by Arf1, and the enzyme also interacts with the Arf1 exchange factor Sec7 (512).…”