Extracellular folate deaminase of Dictyostelium discoideum

A revised folate binding assay was employed to demonstrate the presence of folate receptors on vegetative Dictyostelium discoideum amoebae. These receptors have a dissociation constant of 300 nM and are present at 45000 per cell. We found a pool of receptors attached to the cytoskeleton of vegetative amoebae and these receptors (10000 sites/cell, K d480 nM) remain associated with the cytoskeleton through the first 12 h of development. We discuss the possible roles for these retained receptors in later D. discoideum development.

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“…1) and appeared comparable to earlier reports [26,27] values for folic acid and DAFA of 0.57 and 0.73, respectively (cf. [5]).…”

Section: Identity and Purity Of Dafasupporting

confidence: 79%

Retention of folate receptors on the cytoskeleton of Dictyostelium during development

Tillinghast

Newell

1984

FEBS Letters

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“…Folate—like cAMP in Dictyostelium , LPA in cancer cells, and fMLP in neutrophils—is detected by serpentine receptors and G-proteins [ 12 ]. Cells can also break down folate using secreted and cell-surface folate deaminase [ 13 ], allowing cells to generate folate gradients while responding to them.…”

Section: Resultsmentioning

confidence: 99%

“…We assumed that attractant degradation rate was proportional to the local degrader concentration, and that the Michaelis-Menten constant remained the same as for the bound degrader. As folate deaminase is a large molecule (MW ~40,000, [ 13 ]), we chose a diffusion coefficient that was small relative to that of folate (70 μm 2 /s). One clear difference was a small lag time before the wave forms, due to the time taken for degrader to accumulate.…”

Section: Resultsmentioning

confidence: 99%

Self-Generated Chemoattractant Gradients: Attractant Depletion Extends the Range and Robustness of Chemotaxis

et al. 2016

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Chemotaxis is fundamentally important, but the sources of gradients in vivo are rarely well understood. Here, we analyse self-generated chemotaxis, in which cells respond to gradients they have made themselves by breaking down globally available attractants, using both computational simulations and experiments. We show that chemoattractant degradation creates steep local gradients. This leads to surprising results, in particular the existence of a leading population of cells that moves highly directionally, while cells behind this group are undirected. This leading cell population is denser than those following, especially at high attractant concentrations. The local gradient moves with the leading cells as they interact with their surroundings, giving directed movement that is unusually robust and can operate over long distances. Even when gradients are applied from external sources, attractant breakdown greatly changes cells' responses and increases robustness. We also consider alternative mechanisms for directional decision-making and show that they do not predict the features of population migration we observe experimentally. Our findings provide useful diagnostics to allow identification of self-generated gradients and suggest that self-generated chemotaxis is unexpectedly universal in biology and medicine.

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“…Folate deaminase activity was measured spectrophotometrically as described by Bernstein et al (1981). Protein was determined using the Coomassie Protein Assay (Pierce, Rockford, IL).…”

Section: Other Assaysmentioning

confidence: 99%

Genetic and physiologic modulation of the prestarvation response in Dictyostelium discoideum.

Burdine

Clarke

1995

MBoC

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Throughout vegetative growth, Dictyostelium amoebae secrete an autocrine factor, prestarvation factor, PSF, which accumulates in proportion to cell density. During late exponential growth, PSF induces the expression of several genes whose products are needed for cAMP signaling and cell aggregation. Among these genes are discoidin-I and the 2.4-kb transcript of cyclic nucleotide phosphodiesterase (PDE). We have identified several parameters that modulate expression of one or both of these prestarvation response genes; all effects were monitored in cells growing exponentially on bacteria. Under these conditions, axenic mutants produce higher levels of PSF activity than wild-type cells. Consistent with the high PSF levels, the 2.4-kb PDE transcript is more abundant in axenic strains than wild-type cells at the same cell density. In contrast, the density-dependent induction of discoidin-I is greatly delayed in axenic strains, occurring only at the very end of exponential growth. Analysis of axenic strains of independent origin suggested that this negative effect on discoidin-I expression is attributable to the axenic mutations themselves. The effects of two environmental factors that inhibit the prestarvation response (the bacteria upon which the cells feed and a bacterial product, folic acid) were also analyzed. We found that folate does not account for the inhibitory effect of bacteria. Cells deficient in the G-protein beta subunit, which is thought to be common to all heterotrimeric G-proteins in Dictyostelium, respond to PSF in the same manner as G beta+ cells, and this response is inhibited by bacteria. However, folate has no inhibitory effect on g beta- cells, indicating that folate inhibition is mediated by a heterotrimeric G-protein. In cells lacking the catalytic subunit of protein kinase A, the prestarvation response is severely impaired, but about 3% of the pka- cells manifest an apparently normal density-dependent induction of discoidin-I. This behavior and the heterogeneity of the prestarvation response in wild-type cells lead us to speculate that protein kinase A may not be required for PSF signal transduction per se, but rather may render the cells responsive to PSF. Based on analysis of adenylyl cyclase mutants (aca-), the effect of protein kinase A is not cAMP-dependent.

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Extracellular folate deaminase of Dictyostelium discoideum

Cited by 15 publications

References 28 publications

Retention of folate receptors on the cytoskeleton of Dictyostelium during development

Retention of folate receptors on the cytoskeleton of Dictyostelium during development

Self-Generated Chemoattractant Gradients: Attractant Depletion Extends the Range and Robustness of Chemotaxis

Genetic and physiologic modulation of the prestarvation response in Dictyostelium discoideum.

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