title: The involvement of a protein kinase in phototaxis and gravitaxis of Euglena gracilis.
abstract: The unicellular flagellate Euglena gracilis shows positive phototaxis at low-light intensities (<10 W/m(2)) and a negative one at higher irradiances (>10 W/m(2)). Phototaxis is based on blue light-activated adenylyl cyclases, which produce cAMP upon irradiation. In the absence of light the cells swim upward in the water column (negative gravitaxis). The results of sounding rocket campaigns and of a large number of ground experiments led to the following model of signal perception and transduction in gravitaxis of E. gracilis: The body of the cell is heavier than the surrounding medium, sediments and thereby exerts a force onto the lower membrane. Upon deviation from a vertical swimming path mechano-sensitive ion channels are activated. Calcium is gated inwards which leads to an increase in the intracellular calcium concentration and causes a change of the membrane potential. After influx, calcium activates one of several calmodulins found in Euglena, which in turn activates an adenylyl cyclase (different from the one involved in phototaxis) to produce cAMP from ATP. One further element in the sensory transduction chain of both phototaxis and gravitaxis is a specific protein kinase A. We found five different protein kinases A in E. gracilis. The blockage of only one of these (PK.4, accession No. EU935859) by means of RNAi inhibited both phototaxis and gravitaxis, while inhibition of the other four affected neither phototaxis nor gravitaxis. It is assumed that cAMP directly activates this protein kinase A which may in turn phosphorylate a protein involved in the flagellar beating mechanism.
authors.affiliation: Department of Biology, Cell Biology Division, Friedrich-Alexander University, Staudtstr. 5, 91058 Erlangen, Germany.
authors.forename: Viktor
authors.initials: V
authors.lastname: Daiker
authors.forename: Donat-P
authors.initials: DP
authors.lastname: Häder
authors.forename: Peter R
authors.initials: PR
authors.lastname: Richter
authors.forename: Michael
authors.initials: M
authors.lastname: Lebert
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D001483:Base Sequence; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004789:Enzyme Activation; D005056:Euglena gracilis / Q000187:drug effects / Q000201:enzymology* / Q000502:physiology; D018522:Gravitropism / Q000187:drug effects / Q000502:physiology*; D055537:Light Signal Transduction; D008124:Locomotion / Q000187:drug effects / Q000502:physiology; D008969:Molecular Sequence Data; D010785:Photophosphorylation; D018524:Phototropism / Q000187:drug effects / Q000502:physiology*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D019311:Staurosporine / Q000494:pharmacology
chemical_list: D047428:Protein Kinase Inhibitors; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D000262:Adenylyl Cyclases; D019311:Staurosporine