It takes two transducins to activate the cGMP-phosphodiesterase 6 in retinal rods

Among cyclic nucleotide phosphodiesterases (PDEs), PDE6 is unique in serving as an effector enzyme in G protein-coupled signal transduction. In retinal rods and cones, PDE6 is membrane-bound and activated to hydrolyse its substrate, cGMP, by binding of two active G protein alpha-subunits (G alpha*). To investigate the activation mechanism of mammalian rod PDE6, we have collected functional and structural data, and analysed them by reaction-diffusion simulations. G alpha* titration of membrane-bound PDE6 reveals a strong functional asymmetry of the enzyme with respect to the affinity of G alpha* for its two binding sites on membrane-bound PDE6 and the enzymatic activity of the intermediary 1 : 1 G alpha*. PDE6 complex. Employing cGMP and its 8-bromo analogue as substrates, we find that G alpha*. PDE6 forms with high affinity but has virtually no cGMP hydrolytic activity. To fully activate PDE6, it takes a second copy of G alpha* which binds with lower affinity, forming G alpha*. PDE6. G alpha*. Reaction-diffusion simulations show that the functional asymmetry of membrane-bound PDE6 constitutes a coincidence switch and explains the lack of G protein-related noise in visual signal transduction. The high local concentration of G alpha* generated by a light-activated rhodopsin molecule efficiently activates PDE6, whereas the low density of spontaneously activated G alpha* fails to activate the effector enzyme.This work was funded by Deutsche Forschungsgemeinschaftthrough grant nos. SP 1130/1-1 and SFB 449 to M.H., K.P.H. andC.M.T.S., SFB 740 to F.N., M.H., K.P.H., T.M. and C.M.T.S., a EuropeanResearch Council starting grant (pcCell) to F.N. and a EuropeanResearch Council advanced grant (TUDOR) to K.P.H. E.B. holds aFreigeist-Fellowship from the Volkswagen Foundatio

Rocks rock: the importance of rock formations as resting sites of the Eurasian lynx Lynx lynx

Eurasian lynx Lynx lynx L. are recolonizing parts of their former range in Europe. Not only are lynx strictly protected as a species, but also their habitat and in particular their resting sites are protected. As the known characteristics of lynx resting sites are restricted to vegetation structure, it is difficult to take resting sites into account in planning processes. Here, we show the importance of rock formations for potential resting sites selection and analyzed the frequencies at which GPS-collared lynx returned to potential resting sites in the Bohemian Forest Ecosystem at the border between the Czech Republic and Germany. Lynx showed a strong selection for proximity of rocks for resting site selection, and the distance of potential resting sites to rocks was an important predictor for determining whether lynx return to the resting site or not. Furthermore, the frequency of returns to the resting site was positively influenced by the distance to roads and geomorphology. Our findings highlight the importance of rock formations as resting sites for lynx, which can help with the implementation of concrete protection measures