Characterization of a calmodulin-binding protein that is deficient in trifluoperazine-resistant variants of the macrophage-like cell line J774

Free-Solution, Label-Free Molecular Interactions Studied by Back-Scattering Interferometry

Free-solution, label-free molecular interactions were investigated with back-scattering interferometry in a simple optical train composed of a helium-neon laser, a microfluidic channel, and a position sensor. Molecular binding interactions between proteins, ions and protein, and small molecules and protein, were determined with high dynamic range dissociation constants (Kd spanning six decades) and unmatched sensitivity (picomolar Kd's and detection limits of 10,000s of molecules). With this technique, equilibrium dissociation constants were quantified for protein A and immunoglobulin G, interleukin-2 with its monoclonal antibody, and calmodulin with calcium ion Ca2+, a small molecule inhibitor, the protein calcineurin, and the M13 peptide. The high sensitivity of back-scattering interferometry and small volumes of microfluidics allowed the entire calmodulin assay to be performed with 200 picomoles of solute.

A dominant trifluoperazine resistance gene from Saccharomyces cerevisiae has homology with F0F1 ATP synthase and confers calcium-sensitive growth

The antipsychotic drug trifluoperazine has been long considered a calmodulin inhibitor from in vitro studies but may function in vivo as a more general inhibitor by disturbing ion fluxes and altering the membrane potential. Resistance to trifluoperazine can arise in Saccharomyces cerevisiae cells by alterations in at least three distinct genetic loci. One locus, defined by a spontaneous dominant trifluoperazine resistance mutation (TFP1-408), was isolated and sequenced. The sequence of the TFP1-408 gene revealed a large open reading frame coding for a large protein of 1,031 amino acids with predicted hydrophobic transmembrane domains. A search of existing amino acid sequences revealed a significant homology with F0F1 ATP synthase. Mutant TFP1-408 cells did not grow efficiently in the presence of 50 mM CaCl2, whereas wild-type cells did. Wild-type cells became resistant to trifluoperazine in the presence of 50 mM CaCl2 or 50 mM MgCl2. Mutant cells showed a higher rate of calcium transport relative to wild-type cells. These data suggest that the TFP1 gene product codes for a transmembrane ATPase-like enzyme possibly involved in Ca2+ transport or in generating a transmembrane ion gradient between two cellular compartments.

A dominant trifluoperazine resistance gene from Saccharomyces cerevisiae has homology with F0F1 ATP synthase and confers calcium-sensitive growth

The antipsychotic drug trifluoperazine has been long considered a calmodulin inhibitor from in vitro studies but may function in vivo as a more general inhibitor by disturbing ion fluxes and altering the membrane potential. Resistance to trifluoperazine can arise in Saccharomyces cerevisiae cells by alterations in at least three distinct genetic loci. One locus, defined by a spontaneous dominant trifluoperazine resistance mutation (TFP1-408), was isolated and sequenced. The sequence of the TFP1-408 gene revealed a large open reading frame coding for a large protein of 1,031 amino acids with predicted hydrophobic transmembrane domains. A search of existing amino acid sequences revealed a significant homology with F0F1 ATP synthase. Mutant TFP1-408 cells did not grow efficiently in the presence of 50 mM CaCl2, whereas wild-type cells did. Wild-type cells became resistant to trifluoperazine in the presence of 50 mM CaCl2 or 50 mM MgCl2. Mutant cells showed a higher rate of calcium transport relative to wild-type cells. These data suggest that the TFP1 gene product codes for a transmembrane ATPase-like enzyme possibly involved in Ca2+ transport or in generating a transmembrane ion gradient between two cellular compartments.

Cytoplasmic gels from macrophages. Evidence for the involvement of four proteins in the calcium-dependent solation of actin networks

A method has been devised to study the influence of Ca2+ on the in vitro formation of actin gel networks. Under appropriate conditions low-Ca2+ cytosolic extracts (less than 1 nM) from macrophages rapidly formed a macromolecular complex composed of actin, filamin, alpha-actinin and two new proteins of 70 kDa and 55 kDa. [Pacaud, M. (1986) Eur. J. Biochem. 156, 521-530]. Increasing concentrations of free Ca2+ to 1-2 microM resulted in complete inhibition of the association of 70-kDa protein, a protein which associates actin filaments into parallel arrays. Concentrations of Ca2+ greater than 3 microM caused incorporation of two additional proteins, gelsolin and a 18-kDa polypeptide, with no change in either the actin or alpha-actinin content of the cytoskeletal structures. Use of a polyacrylamide gel overlay technique with 125I-calmodulin revealed that a high-Mr calmodulin-binding protein analogous to spectrin was also associated with these structures when micromolar Ca2+ was present. Similar assays with 45CaCl2 indicated that the 70-kDa protein binds Ca2+ with high affinity. It is thus suggested that Ca2+ might regulate the dynamic assembly of microfilaments through several target proteins, gelsolin, the 70-kDa protein and calmodulin.

Fluphenazine-resistant Saccharomyces cerevisiae mutants defective in the cell division cycle

An fls1 mutant of Saccharomyces cerevisiae, which did not grow in the presence of 30 micrograms of fluphenazine per ml, was isolated. Mutants that were resistant to 90 micrograms of fluphenazine per ml and temperature sensitive for growth were obtained from the fls1 mutant. One fluphenazine-resistance mutation, fsr1, was located near the his7 locus on chromosome II. Growth of the fsr1 mutants at 35 degrees C was arrested after nuclear division. The other group of fluphenazine-resistant mutants, carrying fsr2 mutations, showed Ca2+-dependent growth at 35 degrees C. Growth of the fsr2 mutants at 35 degrees C was arrested at the G2 stage of the cell cycle in Ca2+-poor medium.

Genetic study of the role of calcium ions in the cell division cycle of Saccharomyces cerevisiae: a calcium-dependent mutant and its trifluoperazine-dependent pseudorevertants

A cal1-1 mutant of the yeast Saccharomyces cerevisiae showing Ca2+-dependent growth was isolated. Its growth continued exponentially in Ca2+-rich medium, but stopped in Ca2+-poor medium at 37 degrees C. Mg2+ ions could not replace Ca2+ ions. In Ca2+-poor medium, the mutant cells stopped growing homogeneously at the stage of cell division cycle with a tiny bud. The nucleus in these arrested cells was in the G2 stage, judging from observation after nuclear staining and determination of the DNA content. Trifluoperazine-dependent pseudorevertants, which could grow in the presence of 20 microM to 80 microM trifluoperazine in Ca2+-poor medium at 37 degrees C, were obtained from this cal1-1 mutant. The suppressor mutation, tfr1, itself conferred trifluoperazine resistance. Other calmodulin inhibitors structurally unrelated to trifluoperazine had similar effects to trifluoperazine on these pseudorevertants. These results suggest that Ca2+ ions and a calmodulin play important roles in the yeast cell division cycle at the stage of bud growth and nuclear division.

Serotonin alters the subcellular distribution of a Ca2+/calmodulin-binding protein in neurons of Aplysia

We purified and radioiodinated calmodulin from Aplysia nervous tissue. Using blot analysis, we detected 14 calmodulin-binding proteins in extracts of the abdominal ganglion after gel electrophoresis in NaDodSO4. All 14 components are present in extracts from each of the major central Aplysia ganglia, but their relative proportions differed characteristically from one ganglion to another. When neural components are extracted with nonionic detergents in 2 M glycerol, we obtain a cytoplasmic and a membrane-cytoskeleton fraction. Of the 14 calmodulin-binding proteins, 2 are cytoplasmic, 10 are loosely associated, and 2 remain bound to the membrane-cytoskeleton complex. Treatment of isolated ganglia with serotonin, which has been shown to increase the content of cAMP within neurons, or with dibutyryl cAMP causes the partial dissociation of one of the loosely associated proteins, which has an apparent Mr of 55,000. In extracts prepared in the presence of glycerol and cAMP, this component also is dissociated from the membrane-cytoskeleton complex, but only if ATP is also present. These results suggest that a cAMP-dependent protein phosphorylation controls the subcellular distribution of the Mr 55,000 calmodulin-binding protein, whose state of phosphorylation itself, however, does not appear to be increased by cAMP.