Calmodulin activates prokaryotic adenylate cyclase.

Area of Science:

• Biochemistry
• Molecular Biology
• Microbiology

Background:

• Adenylate cyclase is a key enzyme in cellular signaling.
• Calmodulin is a well-known calcium-binding protein regulating eukaryotic enzymes.
• The presence and function of calmodulin in prokaryotes remain largely unexplored.

Purpose of the Study:

• To investigate the interaction between Bordetella pertussis adenylate cyclase and eukaryotic calmodulin.
• To characterize the properties of this enzyme-calmodulin interaction.

Main Methods:

• Enzyme activity assays measuring adenylate cyclase stimulation.
• Dose-response studies using varying concentrations of calmodulin.
• Inhibition studies using chelators (EGTA) and specific inhibitors (trifluoperazine).
• Chemical modification of calmodulin (methionine oxidation) to assess functional impact.

Main Results:

• Calf brain calmodulin stimulated Bordetella pertussis adenylate cyclase 100- to 1000-fold in a dose-dependent manner.
• Activation was calcium-dependent, inhibited by EGTA, and restored by Ca2+.
• Oxidation of calmodulin's methionine residues abolished its activating ability.
• Trifluoperazine inhibited the calmodulin-activated cyclase.
• Troponin C showed significantly lower potency (<0.01) in stimulating the cyclase compared to calmodulin.

Conclusions:

• Eukaryotic calmodulin can modulate prokaryotic adenylate cyclase activity.
• This interaction shares properties with known calmodulin-regulated systems, including calcium dependence and sensitivity to specific inhibitors.
• This study provides evidence for a functional calmodulin-like effect in a prokaryote, Bordetella pertussis.