Differences in protein phosphorylation in vivo and in vitro between wild type and dunce mutant strains of Drosophila melanogaster

Cloning and chromosomal localization of Drosophila cDNA encoding the catalytic subunit of protein phosphatase 1 alpha. High conservation between mammalian and insect sequences

A 1.2-kb clone containing the full coding sequence of a protein phosphatase 1 catalytic subunit has been isolated from a Drosophila head cDNA library. It encodes a polypeptide of 302 amino acids with a molecular mass of 34.5 kDa. The predicted protein sequence is 92% identical (94% similar) to rabbit protein phosphatase 1 alpha (PP-1 alpha) demonstrating strict conservation of the phosphatase catalytic subunit over a considerable evolutionary distance. Abundant 1.6-kb and 2.5-kb mRNA transcripts were detected throughout Drosophila development. The clone hybridised to four sites on Drosophila salivary gland polytene chromosomes. The major site is at 87B6-12 on the right arm of chromosome 3. In addition, there are three secondary sites, one on the same chromosome at 96A2-5 and two on the X chromosome at 9C1-2 and 13C1-2. Isolation of a further cDNA clone, hybridising to 9C1-2 and encoding part of the catalytic subunit 88% similar to Drosophila PP-1 alpha, proves the existence of at least two transcriptionally active genes for protein phosphatase 1.

Protein kinase C in larval brain of wild-type and dunce memory-mutant Drosophila

Protein kinase C activity has been measured in extracts of larval brain of Drosophila melanogaster, with the synthetic nonapeptide substrate Ala-Ala-Ala-Ser-Phe-Lys-Ala-Lys-Lys-amide. Protein kinase C activity in such extracts is abolished in a Ca2+-dependent manner at 18 degrees C, and partly converted to a form independent of effectors. The decay of protein kinase C activity can be prevented by leupeptin or a crude calpastatin preparation isolated from fly heads, indicating the presence of the Ca2+-dependent neutral protease, calpain, in larval brains. The total protein kinase C levels were nearly the same in wild type and three different dunce "memory-mutant" strains. In contrast, the soluble/particulate activity ratios were different: wild-type, 0.91; dunce M11, 0.46; dunce M11/Df(1)dm75e19, 1.23; dunce2, 0.88. These data suggest that the membrane adherence of protein kinase C in larval brain is governed by the actor of genes other than dunce.

Microtubule-associated cyclic AMP-dependent protein kinase in Drosophila melanogaster

Microtubules were prepared from head extracts of the adult fruit fly, Drosophila melanogaster, by one-step, taxol-assisted polymerization. The microtubular fraction displayed cyclic AMP-dependent protein kinase (protein kinase A) activity, as witnessed by endogenous protein phosphorylation and by protein kinase assay. Microtubule-bound protein kinase A amounts to 4-5% of total soluble kinase activity, which is almost an order of magnitude less than in mammals. The high-molecular-weight microtubule-associated protein-2 (MAP-2), the main binding species for protein kinase A in mammalian brain microtubules, is not detectable in the fly system by protein staining and immunoblotting with anti-pig MAP-2 serum, as well as by hybridization of fly DNA with a cDNA probe for human MAP-2. Cyclic AMP removes a major part of the regulatory (R) subunit of the enzyme from Drosophila microtubules, as demonstrated by enzyme assay, autophosphorylation of R subunit, and quantitating cyclic AMP binding sites. It is proposed that permanently elevated cyclic AMP levels may elute protein kinase A from crucial intracellular binding sites, thereby interfering with signal transduction.

In vitro protein phosphorylation in head preparations from normal and mutant Drosophila melanogaster

We have characterized protein phosphorylation in vitro in subcellular fractions from Drosophila melanogaster heads. Optimal conditions for the incorporation of 32P into proteins, and its dependence on ATP, divalent cations, and cyclic nucleotides have been determined, as well as the effect of inhibitors of ATPase, protein phosphatase, and protein kinase on protein phosphorylation. Among these inhibitors, Zn2+ was found to affect the incorporation of 32P into specific bands and p-hydroxymercuribenzoate was found to be most suited for freezing the activity of both kinases and phosphatases. Cyclic AMP-dependent protein kinase (cAMP-dPK) activity was present in both supernatant (S2) and particulate (P2) fractions, with the majority (60-85%, depending on the homogenization medium) being associated with S2, as determined by phosphorylation of exogenous synapsin I. cAMP-dPK catalyzed the phosphorylation of at least 18 endogenous polypeptides in S2 and at least 10 endogenous polypeptides in P2. These proteins could be classified on the basis of the extent of stimulation of phosphorylation by cyclic nucleotides, dependence on cyclic nucleotide concentration, and rate of phosphorylation. A phosphoprotein of 51 kilodaltons (pp51) was a major component of the S2 and P2 fractions and displayed properties expected from the regulatory subunit of the cAMP-dPK, R-II. A phosphoprotein doublet of approximately 37 kilodaltons (pp37) was stimulated to the largest extent by cAMP in the P2 and S2 fractions. The phosphorylation of several proteins in both fractions was significantly lowered by the mammalian Walsh inhibitor of cAMP-dPK, whereas in some cases the stimulation of phosphorylation of the same proteins by exogeneous cAMP was relatively small. Phosphoproteins from two learning mutants known to be deficient in cAMP metabolism, dnc and rut, were analyzed for their extent of phosphorylation in the presence of a stable cAMP analogue; no significant differences from normal were detected, suggesting that the genetic defect in cAMP metabolism is not accompanied by constituent abnormalities in phosphorylated substrates in the adult fly, and that the physiological defects in these mutants result from aberrations in the interaction of the cAMP cascade with normal substrates. The majority of Ca2+/calmodulin kinase activity (80-90%, depending on the homogenization procedure) was associated with S2, as revealed by phosphorylation of exogenous synapsin I. Two endogenous substrates for this kinase in P2 had molecular masses of approximately 45 and 87 kilodaltons. At least 11 substrates for the Ca2+/calmodulin-dependent kinase were detected in S2.(ABSTRACT TRUNCATED AT 400 WORDS)

The protein phosphatases of Drosophila melanogaster and their inhibitors

Protein phosphatases-1, 2A and 2B have been identified in membrane and soluble fractions of Drosophila melanogaster heads. Similarities between Drosophila and mammalian protein phosphatase-1 included specificity for the beta subunit of phosphorylase kinase, sensitivity to inhibitor-1 and inhibitor-2, inhibition by protamine, retention by heparin-Sepharose and selective interaction with membranes. In addition, an inactive form of protein phosphatase-1, termed protein phosphatase-1I, was detected in the soluble fraction that could be activated by preincubation with MgATP and mammalian glycogen synthase kinase-3. Inhibitor-2 partially purified from Drosophila had an identical molecular mass to its mammalian counterpart, and recombined with mammalian protein phosphatase-1 to form a hybrid protein phosphatase-1I. Similarities between Drosophila and mammalian protein phosphatase-2A included preferential dephosphorylation of the alpha subunit of phosphorylase kinase, insensitivity to inhibitors-1 and -2, activation by protamine, exclusion from heparin-Sepharose and apparent molecular mass. A Ca2+-dependent calmodulin-stimulated protein phosphatase (protein phosphatase-2B) that was inhibited by trifluoperazine was identified in the soluble fraction. The remarkable similarities between Drosophila protein phosphatases and their mammalian counterparts are indicative of strict phylogenetic conservation and demonstrate that the procedures used to classify mammalian protein phosphatases have a wider application. Characterisation of the Drosophila phosphatases will facilitate genetic analysis of dephosphorylation systems and their possible roles in neuronal and behavioural plasticity in Drosophila.

Altered autophosphorylation of adenosine 3',5'-phosphate-dependent protein kinase in the dunce memory mutant of Drosophila melanogaster

The phosphorylation-dephosphorylation, in the presence of adenosine 5'-[gamma-32P]triphosphate, of a polypeptide of apparent molecular mass 53,000 has been compared in head homogenates of wild type and memory mutant dunceM11 strains of Drosophila melanogaster. In both strains, labelling of the 53 kilodalton protein required exogenous adenosine 3',5'-phosphate (cAMP), but in dunceM11 cAMP at higher concentration (above approximately 3 microM) caused the rapid disappearance of the label. This differential dephosphorylation can be attributed to the lack of a cAMP-specific phosphodiesterase isoenzyme in the mutant. Several lines of evidence indicate that the 53 kilodalton protein is identical with the regulatory subunit of cAMP-dependent protein kinase. The findings suggest that in the mutant's nerve cells the state of phosphorylation of the regulatory subunit of cAMP-dependent protein kinase is altered, which may contribute to the biochemical disorder leading to the memory deficit.