Calmodulin confers calcium sensitivity on ciliary dynein ATPase

Area of Science:

• Biochemistry
• Cell Biology
• Molecular Motors

Background:

• Dyneins are crucial motor proteins in cilia and flagella.
• Calcium ions (Ca++) play a role in regulating ciliary function.
• Calmodulin is a key calcium-binding protein involved in signal transduction.

Purpose of the Study:

• To investigate the interaction between Tetrahymena dyneins and calmodulin.
• To determine if calmodulin mediates calcium-dependent regulation of dynein ATPase activity.
• To characterize the binding sites and activation mechanisms.

Main Methods:

• Extraction of demembranated Tetrahymena cilia using Tris-EDTA or KCl.
• Assays of dynein ATPase activity in the presence of Ca++ and calmodulin.
• Calmodulin affinity chromatography (calmodulin-Sepharose-4B).
• Gel electrophoresis for protein component analysis.
• Use of 35S-labeled Tetrahymena calmodulin.

Main Results:

• Both 14S and 30S dyneins exhibit Ca++-dependent ATPase activity.
• Calmodulin significantly potentiates this activity, with different concentrations required for 14S and 30S dyneins.
• Tetrahymena and bovine brain calmodulin show similar efficacy, while troponin C is less effective.
• Ca++-dependent calmodulin-binding sites were identified on both dynein forms and axonemes.
• Purified 14S and 30S dyneins revealed distinct high molecular weight protein components.

Conclusions:

• Tetrahymena 14S and 30S dyneins possess Ca++-dependent calmodulin-binding sites.
• Calmodulin mediates the Ca++-regulation of dynein ATPases in Tetrahymena cilia.
• This interaction is essential for controlling ciliary motility.