D. discoideum

In recent years, work by Loomis and co-workers has raised the possibility that cAMP oscillations in D. discoideum may originate from an intracellular regulatory network rather than from the mixed positive and negative feedback exerted by extracellular cAMP [84, 85]. These authors obtained evidence for an intracellular feedback loop involving MAP kinase and the cAMP-dependent protein kinase, PKA. The later enzyme would inactivate adenylate cyclase after a cAMP pulse. Numerical simulations of a model based on this intracellular negative feedback loop confirm that it can produce sustained oscillations of cAMP. 

Cleavage of the -850-residue SI heads with trypsin yields mainly three large fragments that correspond to structural domains of the intact protein as shown in Fig. 19-15. They are known as the 25-kDa (N-terminal), 50-kDa, and 20-kDa fragments, and for myosin from D. discoideum correspond to residues 1 to 204,216 to 626, and 647 to 843, respectively. The ATP-binding site is in a deep cleft between the 20-kDa and 50-kDa... 

In all cases the cells also utilize cAMP as an internal second messenger. For D. discoideum the components of the chemotactic-aggregation system include a 41-kDa cAMP receptor on the outside, adenylate cyclase, an extracellular diesterase that specifically hydrolyzes the cAMP to AMP, and a diesterase inhibitor protein.35 227-230 The inhibitor keeps the phosphodiesterase largely inactive initially, but when cAMP concentrations build up synthesis of the inhibitor is repressed and the cAMP is hydrolyzed, a necessary condition for retaining sensitivity of the receptors for the arriving pulses of cAMP. 

The stability of the reagent to the assay conditions should also be ascertained. The instability of azides and diazo compounds towards thiols was mentioned earlier, and it would be prudent to ensure that all new reagents whether they contain familiar photoactivatable groups or not are stable to the prevailing chemical and enzymatic conditions. In an attempt to label the cAMP receptor of D. discoideum, Wallace and Frazier (1979b) found that 8-N rcAMP was converted to NrAMP by the phosphodiesterase of a crude membrane preparation. The NrAMP specifically labeled actin and not the cAMP receptor. 

In the slime mould, Dictyostelium discoideum, a STAT-like DNA-binding protein, DIF (the differentiation-inducing factor), is expressed. DIF is about 700 amino-acid residues long, and has substantial homology with mammalian STATs. DIF is, like STAT, activated by phosphorylation of tyrosines. It is essential for differentiation of the stalk cells of D. discoideum A The long evolutionary path that the STATs have travelled from Dictyostelium to mammals underlines their conserved and essential role as signal transmitters and transcriptional activators in early development. 

That more than six phosphates can fit onto an inositol ring was first discovered in D. discoideum (42) and... 

All coronins examined to date (with the exception of mammalian coronin 7) bind to F-actin in vitro and localize to aetin-rich cellular structures, underscoring the conservation and importance of the coronin-F-actin interaction. Genetic disruptions of coronin in S. cerevisiae, D. discoideum, C. degans, D. melanogaster, X. laevis and mammals have further demonstrated the important roles coronins play in a wide variety of actin-based cellular processes (e.g., phagocytosis, endocytosis, cytokinesis, cell motility) and physiological functions (e.g., early embryonic development and lymphocyte function) (see Fig. 3).i -22.2 . 26... 

Coronin 7 (DCrn7) is the second coronin like protein ini), discoideum and the orthologue of the human Coronin 7 (Fig. 1).D. discoideum DCrn7 and human Coronin 7 share high homology and both possess two WD40-core repeat structures that are separated by a PST-domain (proline, serine, threonine rich region) of unknown function. ... 

Interestingly, there is an orthologue of pod-2 found in D. discoideum, accA (DDB0187917), which is also involved in fatty acid biosynthesis. If there is a link between POD-1 and pod-2 there might also be a direct or indirect cooperation ofD. discoideum Crn7 andaccA. Moreover, C. elegans... 

Uncommon caibohydrate-pepUde linkages identified in (a) human RNase 2 and (b) proteinase I of D. discoideum... 

CSP circumsporozoite protein Ddp2 D. discoideum plasmid 2 FSH follicle-stimulating hormone GABA y-aminobutyric acid... 

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