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The cyclic nucleotide specificity of eight cAMP-binding proteins in Dictyostelium discoideum is correlated into three
M Van Ments-Cohen1, P J Van Haastert
1Zoological Laboratory, Leiden University, The Netherlands.
Abstract:
cAMP is a mediator of inter- and intracellular events in Dictyostelium discoideum and is thought to act through specific receptors. Eight forms of cAMP-binding proteins have been described in this organism: four forms of a cell surface receptor, a cell surface and extracellular phosphodiesterase, an intracellular cAMP-dependent protein kinase (CAK), and a recently identified cAMP-binding protein (CABP1) that is present on the cell surface, in the cytoplasm, and in the nucleus. In this study we have analyzed the cyclic nucleotide specificity of these cAMP-binding proteins using 13 derivatives of cAMP with modifications in the adenine, ribose, and phosphate moiety. The results suggest that the cAMP-binding proteins belong to three groups: (i) four forms of the cell surface receptor, (ii) two forms of an intracellular receptor (CABP1 and CAK), and (iii) cell surface and extracellular phosphodiesterase. cAMP is probably bound to the surface receptors in the anti conformation in a hydrophobic cleft of the receptor with essential interactions at N6H2' and O3'. In contrast, cAMP is probably bound to CAK and CABP1 in the syn conformation with essential interactions at O2', O3', O5', and exocyclic oxygen. Finally, binding of cAMP to phosphodiesterase involves only O3' and exocyclic oxygen. The cyclic nucleotide specificity of cAMP-induced processes in D. discoideum indicates that the cell surface receptors participate in the transduction of the cAMP signal during chemotaxis and cell differentiation. Functions for CABP1 and CAK in these processes are presently elusive.
Insights
Cyclic adenosine monophosphate (cAMP) binding proteins in Dictyostelium discoideum were analyzed for cyclic nucleotide specificity. Results revealed three distinct binding groups, suggesting specific roles in cellular signaling and differentiation.
Area of Science:
- Molecular Biology
- Biochemistry
- Cell Biology
Background:
- Cyclic adenosine monophosphate (cAMP) is a crucial second messenger regulating inter- and intracellular events in Dictyostelium discoideum.
- Eight cAMP-binding proteins have been identified, including cell surface receptors, phosphodiesterase, cAMP-dependent protein kinase (CAK), and cAMP-binding protein 1 (CABP1).
Purpose of the Study:
- To investigate the cyclic nucleotide specificity of various Dictyostelium discoideum cAMP-binding proteins.
- To elucidate the binding interactions and conformational preferences of cAMP with different protein targets.
Main Methods:
- Analysis of cAMP-binding proteins using 13 cAMP derivatives with modifications in adenine, ribose, and phosphate moieties.
- Characterization of binding specificity and interactions for cell surface receptors, intracellular receptors (CABP1, CAK), and phosphodiesterase.
Main Results:
- Dictyostelium discoideum cAMP-binding proteins were classified into three groups based on cyclic nucleotide specificity: cell surface receptors, intracellular receptors (CABP1 and CAK), and phosphodiesterase.
- Specific binding interactions and conformations (anti vs. syn) were proposed for cAMP binding to each group.
- Cell surface receptors likely mediate cAMP signal transduction in chemotaxis and differentiation.
Conclusions:
- The distinct cyclic nucleotide specificities of cAMP-binding proteins suggest specialized functions in Dictyostelium discoideum.
- Cell surface receptors play a key role in cAMP signal transduction for chemotaxis and differentiation.
- The precise functions of intracellular receptors CABP1 and CAK in these processes remain to be determined.