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Guanine nucleotides modulate the function of chemotactic cyclic AMP receptors in Dictyostelium discoideum
Abstract:
Guanosine di- and triphosphates specifically decrease the affinity of chemotactic cAMP receptors in isolated Dictyostelium discoideum membranes. The K0.5 was increased from 50 nM to 150 nM. Receptors were shown to be heterogeneous in dissociation kinetics. In the absence of guanine nucleotides three dissociation processes could be resolved, having first order rate constants of 8.7 X 10(-4), 1.3 X 10(-2), and higher than 0.1 s-1. Guanine nucleotides decreased the affinity for cAMP by transforming the slowest dissociating receptor form (KD is 8 nM) to forms dissociating more rapidly. Our data indicate that a guanine nucleotide binding protein (G-protein) is involved in the transduction of the cAMP signal in D. discoideum.
Insights
Guanosine nucleotides reduce cAMP receptor affinity in Dictyostelium discoideum. This suggests a guanine nucleotide-binding protein (G-protein) mediates the cAMP signal transduction pathway in this organism.
Area of Science:
- Cellular signaling
- Biochemistry
- Molecular biology
Background:
- Chemotaxis is crucial for cellular communication and development in organisms like Dictyostelium discoideum.
- Cyclic adenosine monophosphate (cAMP) acts as a key chemoattractant in Dictyostelium discoideum.
- Understanding receptor-ligand interactions is fundamental to deciphering signal transduction pathways.
Purpose of the Study:
- To investigate the effect of guanosine di- and triphosphates on the affinity of chemotactic cAMP receptors.
- To characterize the heterogeneity of cAMP receptor dissociation kinetics.
- To elucidate the role of guanine nucleotides in cAMP signal transduction.
Main Methods:
- Isolation of Dictyostelium discoideum membranes.
- Measurement of cAMP receptor binding affinity (K0.5) in the presence and absence of guanine nucleotides.
- Analysis of receptor dissociation kinetics using first-order rate constants.
Main Results:
- Guanosine di- and triphosphates significantly decreased the affinity of cAMP receptors, increasing K0.5 from 50 nM to 150 nM.
- Receptors exhibited heterogeneous dissociation kinetics, with three distinct processes observed.
- Guanine nucleotides modulated receptor affinity by converting slower-dissociating forms to faster-dissociating ones.
Conclusions:
- Guanine nucleotides play a critical role in regulating cAMP receptor affinity.
- The observed modulation suggests the involvement of a guanine nucleotide-binding protein (G-protein).
- A G-protein is likely integral to the cAMP signal transduction pathway in Dictyostelium discoideum.