Microtubules accelerate ADP release by dynein

Area of Science:

• Biochemistry
• Molecular Biology
• Cellular Motor Proteins

Background:

• Dynein is a motor protein crucial for cellular transport.
• Understanding dynein's ATPase mechanism is key to cellular function.
• Microtubules are known to regulate dynein activity.

Purpose of the Study:

• To elucidate the mechanism by which microtubules activate dynein's ATPase activity.
• To investigate the role of phosphate-water oxygen exchange in dynein-microtubule interactions.
• To determine whether microtubules affect phosphate or ADP release from dynein.

Main Methods:

• Studying phosphate-water oxygen exchange reactions catalyzed by dynein.
• Measuring ATP hydrolysis rates in the presence and absence of microtubules.
• Analyzing the effect of varying ADP concentrations on dynein-microtubule binding and dissociation.
• Quantifying binding and dissociation rates of dynein to microtubules.

Main Results:

• Microtubules inhibited the rate of medium phosphate-water exchange during net ATP hydrolysis.
• Inhibition of exchange correlated with microtubule activation of ATP turnover, without affecting the partition coefficient.
• Microtubules inhibited phosphate-water exchange in the presence of ADP and Pi.
• ADP release, not phosphate release, was identified as the rate-limiting step enhanced by microtubules.
• ADP binding to the microtubule-dynein complex was characterized, with a fast ADP dissociation rate from the dynein-ADP complex.

Conclusions:

• Microtubules activate dynein ATPase primarily by increasing the rate of ADP release.
• The findings support the existence of a high-energy dynein-ADP intermediate.
• Dynein's interaction with microtubules is crucial for regulating its enzymatic activity and power stroke.