Dictyostelium studies

Studies in yeasts (Saccharomyces cerevisiae, Schizo-saccharomyces pombe), slime mould (,Dictyostelium discoideum), worm (Caenorhabditis elegans), fly (Drosophila melanogaster) and mammalian systems have all contributed to our understanding of TOR signalling. 

These studies demonstrate the general mechanism of synchronization of biochemical systems, which I expect to be operative in even more complex systems, such as the mitochondrial respiration or the periodic activity of the slime mold Dictyostelium discoideum. As shown in a number of laboratories under suitable conditions mitochondrial respiration can break into self-sustained oscillations of ATP and ADP, NADH, cytochromes, and oxygen uptake as well as various ion transport and proton transport functions. It is important to note that mitochondrial respiration and oxidative phosphorylation under conditions of oscillations is open for the source, namely, oxygen, as well as with respect to a number of sink reactions producing water, carbon dioxide, and heat. 

Dumas, C. Lebras, G. Wallet, V. Lacombe, M.-L. Veron, M. Janin, J. Crystallization and preliminary X-ray diffraction studies of nucleoside diphosphate kinase from Dictyostelium discoideum. J. Mol. Biol., 217, 239-240 (1991)... 

Early studies revealed that the 3, 5 -cyclic phosphate diesterase is present in all mammalian tissues (38, 33, 36), being most active in cerebral cortex (36, 37). It has also been identified in extracts of liver fluke (Fasciola hepatica), the common earthworm (Lumbricus terrestris), and fly larvae (36) and it has been studied in marine organisms (38), the cellular slime mold Dictyostelium discovdeum (39, AO), and in E. coli (Al). The enzyme has been partially purified from beef heart (30), dog heart, (A8) and bovine brain (37, A3). No highly purified preparations have yet been obtained and most studies have been performed with relatively crude preparations. 

NHS esters of D-biotin have been used in many applications, including the biotinylation of rat IgE to study receptors on murine lymphocytes (Lee and Conrad, 1984), in the development of an immunochemical assay for a postsynaptic protein and its receptor (LaRochelle and Froehner, 1986a), in the study of plasma membrane domains by biotinylation of cell surface proteins in Dictyostelium disoideum amoebas (Ingalls et al., 1986), and for the detection of blotted proteins on nitrocellulose membranes after transfer from polyacrylamide electrophoresis gels (LaRochelle and Froehner, 1986b). 

Spectrin is a common component of the submembranous cytoskeleton. It was first identified as a major constituent of the erythrocyte membrane cytoskeleton, but has since been found in many other vertebrate tissues as well as in the nonvertebrates Drosophila, Acanthamoeba, Dictyostelium, and echinoderms (Bennett and Condeelis, 1988 Byers et al., 1992 Dubreuil et al., 1989 Pollard, 1984 Wessel and Chen., 1993). The ease with which spectrin could be isolated from erythrocyte ghosts made it an ideal candidate for the study of the biochemical processes involved in the assembly and organization of the cytoskeleton (Gratzer, 1985). 

Studies of the pyrene label on actin indicate that the ATP-induced dissociation of actin occurs via a three-step process (steps 1, 2, and c, Scheme 1 Millar and Geeves, 1983). Initial fast equilibrium binding of ATP (controlled by and probably diffusion limited) is followed by an isomerization that alters the environment of the pyrene label on actin. This isomerization is fast in myosin II and much slower for some non-muscle myosins (-500 s-1 for Dictyostelium myosin II Kurzawa et al., 1997 >1000 s-1 for rabbit skeletal myosin II, Geeves andjeffries, 1988 100 s-1 for myosin lb at 20°C Coluccio and Geeves, 1999) and is accompanied by a very rapid... 

It has long been surmised that switch-2 movement and the concomitant swinging of the lever arm must be controlled by binding to and detachment from the actin filament to avoid futile consumption of ATP. However, direct evidence was lacking because near-atomic resolution crystal structures are necessarily obtained in the absence of the filament. Now, crystal structures of Dictyostelium myosin II (Reubold et at, 2003) and chicken myosin-V (Coureux et al., 2003) have revealed that the switch-1 motif can also exist in open and closed conformations. It has been inferred that switch-1 opening may be coupled to cleft closure and tight binding of the myosin head to the actin filament. This conclusion is supported by electron microscopy (Holmes et al., 2003) and fluorescence spectroscopy (Conibear et al., 2003) studies of the acto-myosin complex, which show that the concepts derived from crystal structures of isolated myosin heads are indeed valid for the functional complex. 

Janssen K. P. and Schleicher M. (2001b) Dictyostelium discoideum a genetic model system for the study of professional phagocytes. Profilin, phosphoinositides and the Imp gene family in Dictyostelium. Biochim. Biophys. Acta. 1525, 228-233. 

The essentials of the major pathway to Ins P6 in yeast nuclei can be summarized as follows Ins — Ptdlns, catalyzed by Ptdlns synthase Ptdlns —>PtdIns(4,5) P2, catalyzed sequentially by two specific kinases PtdIns(4,5)P2—>Ins (1,4,5)P3, catalyzed by a Ptdlns-specific phospholipase C Ins(l,4,5)P3—>—> Ins(l,3,4,5,6)P5, catalyzed by an Ins(l,4,5)P3 3-/6-kinase Ins(l,3,4,5,6)P5 —> Ins P6, catalyzed by an Ins(l,3,4,5,6)P5 2-kinase. This is now viewed as the canonical PLC-dependent pathway. Recent genetics studies have shown that this pathway is also critical to Ins P6 synthesis in Drosophila and rat cells (Fujii and York, 2004 Seeds et al., 2004). In contrast, the sole genetic evidence in any organism for a PLC-independent pathway like that described above in Dictyostelium and Spirodela, one that proceeds solely via soluble Ins phosphates, consists of one elegant study using Dictyostelium (Drayer et al., 1994). In this study the presence and levels of the whole series of Ins phosphates typical of a wild-type Dictyostelium, including Ins(l,4,5)P3 and Ins P6, where shown to be essentially identical in a PLC-null line. Thus some pathway to Ins(l,4,5)P3 and Ins P6 independent of PLC must exist in this organism. 

Dictyostelium discoideum is a cellular slime mold, an amoeba. It is a preferred object for the study of cell locomotion, chemotaxis and differentiation. 

A very elegant study [67] from Harwood and Ryves demonstrated that Ii+ is non-competitive with respect to peptide substrate or ATP and instead inhibits GSK-3P by competing with Mg ions. li showed a similar mode of inhibition with both GSK-3a and GskA (the Dictyostelium GSK-3 protein ho-mologue) which differs from GSK-3 in the catalytic core by 29%. 

TCA Cycle in Dictyostelium A Case Study Generality of the Power-Law Formalism Conclusions Summary... 

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