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Microtubule-associated cyclic AMP-dependent protein kinase in Drosophila melanogaster
1Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, Budapest.
Abstract:
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.
Insights
Fruit fly microtubules possess protein kinase A activity, though at lower levels than mammals. Elevated cyclic AMP may disrupt this signaling by detaching the enzyme
Area of Science:
- Cell Biology
- Biochemistry
- Molecular Biology
Background:
- Microtubules are essential cytoskeletal components involved in various cellular processes.
- Protein kinase A (PKA) is a crucial enzyme in cyclic AMP-mediated signal transduction pathways.
- Understanding PKA's interaction with microtubules provides insights into cellular regulation.
Purpose of the Study:
- To investigate the presence and characteristics of protein kinase A (PKA) associated with microtubules in Drosophila melanogaster.
- To compare the PKA-microtubule interaction in Drosophila with mammalian systems.
- To explore the role of cyclic AMP in regulating PKA binding to Drosophila microtubules.
Main Methods:
- Preparation of microtubules from adult fruit fly head extracts using taxol-assisted polymerization.
- Assays for endogenous protein phosphorylation and protein kinase activity to detect PKA.
- Immunoblotting and DNA hybridization to assess the presence of microtubule-associated protein-2 (MAP-2).
- Enzyme assays and cyclic AMP binding site quantification to study PKA subunit dynamics.
Main Results:
- Drosophila microtubules exhibit cyclic AMP-dependent protein kinase A activity.
- Microtubule-bound PKA activity is significantly lower in Drosophila compared to mammals.
- The mammalian PKA-binding protein MAP-2 is undetectable in Drosophila.
- Cyclic AMP effectively removes the regulatory subunit of PKA from Drosophila microtubules.
Conclusions:
- Drosophila microtubules bind and contain active protein kinase A.
- The absence of MAP-2 and lower PKA binding suggest differences in microtubule-PKA interactions between flies and mammals.
- Elevated cyclic AMP levels may disrupt intracellular signaling by causing PKA detachment from microtubules in Drosophila.