A model for cyclic AMP-chemoreceptor interaction in Dictyostelium discoideum (original) (raw)
Related papers
Biochemistry, 1986
Aggregating Dictyostelium discoideum cells possess receptors for the chemoattractant cAMP on their cell surface. Membranes enriched in these receptors were isolated. Kinetic studies indicated the same receptor heterogeneity in membranes as found for intact cells [van Haastert, P. J. M., & De Wit, R. J. W. (1984) J. Biol. Chem. 259, 13321-133281. Dissociation kinetics revealed at least three receptor forms: one form, called SS, with kl = 0.9 X = 1.3 X s-l and KD = -6 nM; and one or more forms, called F, with kl > 0.1 s-'. The contribution of the SS form to the dissociation process was lower in the presence of millimolar concentrations of cAMP compared to dissociation induced by dilution only. Guanosine di-and triphosphates decreased the affinity of membranes for cAMP by increasing the dissociation rate of the CAMP-receptor complex. This was shown to result from a reduction in the number of sites of the slowly dissociating, high-affinity receptor form SS and probably also the high-affinity form S. Because the total number of cAMP binding sites was not changed by guanine nucleotides, it is inferred that the SS and S receptor forms are converted to other more rapidly dissociating receptor forms with lower affinities than SS and S. We propose that cAMP receptors in Dictyostelium membranes interact with G protein which binds guanosine di-and triphosphates. The different complexes between receptor and occupied or unoccupied G protein explain the different receptor forms and their interconversions. s-I and KD = 6.5 nM; one form, called S, with
1986
Extracellular molecules regulate gene expression in eucaryotes. Exogenous cyclic AMP (cAMP) affects the expression of a large number of developmentally regulated genes in Dictyostelium discoideum. Here, we determine the specificity of the receptor(s) which mediates gene expression by using analogs of cAMP. The order of potency with which these analogs affect the expression of specific genes is consistent with the specificity of their binding to a cell surface receptor and is distinct from their affinity for intracellular cAMP-dependent protein kinase. Dose-response curves with cAMP and adenosine 3',5'-monophosphorothioate, a nonhydrolyzable analog, revealed that the requirement for high concentrations of exogenous cAMP for regulating gene expression is due to the rapid degradation of cAMP by phosphodiesterase. The addition of low concentrations of cAMP (100 nM) or analogs in pulses also regulates gene expression. Both the genes that are positively regulated by exogenous cAMP and the discoidin gene, which is negatively regulated, respond to cAMP analogs to the same degree. Genes expressed in prespore or prestalk cells are also similarly regulated. These data suggest that the effects are mediated through the same receptor. The specificity of this receptor is indistinguishable from that of the well-characterized cell surface cAMP receptor.
Dictyostelium discoideum cell membranes contain masked chemotactic receptors for cyclic AMP
FEBS Letters, 1984
Aggregating Dictyostelium dz3coideum cells possess highly specific receptors for the chemoattractant CAMP on their cell surface. Isolated membranes as well as intact cells are shown to contain a large number of latent CAMP receptors. These are reversibly unmasked in the presence of a high salt concentration (0. 1-2 M) or in the presence of millimolar concentrations of CaZ+.
Aggregating Dictyostelium discoideum cells possess receptors for the chemoattractant cAMP on their cell surface. Membranes enriched in these receptors were isolated. Kinetic studies indicated the same receptor heterogeneity in membranes as found for intact cells [van Haastert, P. J. M., & De Wit, R. J. W. (1984) J. Biol. Chem. 259, 13321-133281. Dissociation kinetics revealed at least three receptor forms: one form, called SS, with kl = 0.9 X = 1.3 X s-l and KD = -6 nM; and one or more forms, called F, with kl > 0.1 s-’. The contribution of the SS form to the dissociation process was lower in the presence of millimolar concentrations of cAMP compared to dissociation induced by dilution only. Guanosine di- and triphosphates decreased the affinity of membranes for cAMP by increasing the dissociation rate of the CAMP-receptor complex. This was shown to result from a reduction in the number of sites of the slowly dissociating, high-affinity receptor form SS and probably also the high-affinity form S. Because the total number of cAMP binding sites was not changed by guanine nucleotides, it is inferred that the SS and S receptor forms are converted to other more rapidly dissociating receptor forms with lower affinities than SS and S. We propose that cAMP receptors in Dictyostelium membranes interact with G protein which binds guanosine di- and triphosphates. The different complexes between receptor and occupied or unoccupied G protein explain the different receptor forms and their interconversions.
A Model Based on Receptor Desensitization for Cyclic AMP Signaling in Dictyostelium Cells
Biophysical Journal, 1987
We analyze a model based on receptor modification for the cAMP signaling system that controls aggregation of the slime mold Dictyostelium discoideum after starvation. The model takes into account both the desensitization of the cAMP receptor by reversible phosphorylation and the activation of adenylate cyclase that follows binding of extracellular cAMP to the unmodified receptor. The dynamics of the signaling system is studied in terms of three variables, namely, intracellular and extracellular cAMP, and the fraction of receptor in active state. Using parameter values collected from experimental studies on cAMP signaling and receptor phosphorylation, we show that the model accounts qualitatively and, in a large measure, quantitatively for the various modes of dynamic behavior observed in the experiments: (a) autonomous oscillations of cAMP, (b) relay of suprathreshold cAMP pulses, i.e., excitability, characterized by both an absolute and a relative refractory period, and (c) adaptation to constant cAMP stimuli. A two-variable version of the model is used to demonstrate the link between excitability and oscillations by phase plane analysis. The response of the model to repetitive stimulation allows comprehension, in terms of receptor desensitization, of the role of periodic signaling in Dictyostelium and, more generally, the function of pulsatile patterns of hormone secretion.
Biochimica et Biophysica Acta (BBA) - General Subjects, 1980
A photosensitive, radioactive analogue of cyclic adenosine monophosphate, 8-azido-adenosine 3',5'-[32P]monophosphate (8-N3-cychc AMP), was used to label the cyclic AMP binding proteins of Dzctyostelium discoideum. During development cytosolic proteins appear which are specifically labeled by the photoaffinity agent. The proteins are developmentally regulated since they are only found in starved, developing cells. Unlabeled cyclic AMP competes specifically with the labeled analogue for protein binding sites in contrast to unlabeled 5'-AMP which does not compete. A mutant which develops spores but is deficient in stalk cell production produces a different set of cyclic AMP binding proteins from the parent strain.
1985
A developmentally regulated cyclic AMP-dependent protein kinase has been recently reported in Dictvostelium discoideum. This report describes some of the physical and kinetic properties of the cAMP dependent holoenzyme and its subunits. Gel filtration data suggests a holoenzyme Mr of-l70,000-l90,000, and catalytic and regulatory subunit Mrs of 40,000 and 49,000, respectively. These molecular weight determinations are compatible with an RZCZ subunit arrangement of the holoenzyme. Kinase activity required the presence of Mg2+ but cAMP binding to the enzyme was not dependent on divalent metal ions. The pH optimum for kinase activity was 7.5; the cAMP binding activity was not affected over a pH range of 5.0-10.0. The holoenzyme and isolated regulatory subunit had identical cAMP Kds of 28 nM. Cyclic AMP was able to dissociate the subunits when analyzed by density gradient centrifugation. Histone VII-S activated the subunits in the absence of cAMP but did not produce their dissociation. In contrast to the gel 2.
Journal of Biological Chemistry
The Journal of biological chemistry, 1988
In Dictyostelium discoideum amoebae, cAMP-induced phosphorylation of the surface cAMP receptor is associated with a discrete transition in its electrophoretic mobility. The native and modified forms of the receptor are designated R and D (Mr = 40,000 and 43,000). The relationship of the number of receptors which are modified as a function of the receptors which bind cAMP was investigated. Modification was assessed by determining the amounts of R and D forms in Western blots which detect all receptors whether or not they are exposed on the surface. Cyclic AMP or the analog, adenosine 3',5'-monophosphorothioate ((Rp)-cAMPS), induced a loss of cAMP-binding activity (down-regulation), which was not accompanied by a loss of the receptor protein. About 60% of the receptors do not bind cAMP in the absence of Ca2+ and are unmasked by 10 mM Ca2+. However, the fraction of receptors which are modified in response to cAMP is equal in the absence or presence of Ca2+. (Rp)-cAMPs induces d...