Spire2 and Rab11a synergistically activate myosin-5b motor function

Area of Science:

• Cell Biology
• Molecular Motor Function
• Cytoskeletal Dynamics

Background:

• Cellular vesicle transport relies on motor proteins and cytoskeletal networks.
• Myosin-5b (Myo5b), Spire, and Rab11a form a complex for long-distance vesicle transport in mouse oocytes.
• The regulatory mechanism of the Myo5b/Spire/Rab11a complex is not well understood.

Purpose of the Study:

• To elucidate the intermolecular regulation of the Myo5b/Spire/Rab11a complex.
• To investigate how Spire2 and Rab11a activate Myo5b motor activity.
• To understand the mechanism of vesicle transport in metaphase mouse oocytes.

Main Methods:

• Protein expression and purification of Myo5b, Spire2, and Rab11a.
• In vitro ATPase activity assays to measure motor protein activity.
• Pulldown assays to assess protein complex formation.
• Single-molecule motility assays to observe vesicle transport dynamics.

Main Results:

• Spire2 and Rab11a are essential for activating Myo5b motor activity under physiological conditions.
• The GTBM fragment of Spire2 activates Myo5b ATPase activity, with Rab11a further enhancing this activation.
• Activation of Myo5b involves the disruption of its head-tail interaction.
• Spire2 and Rab11a synergistically stimulate Myo5b motility at the single-molecule level.

Conclusions:

• Myo5b, Spire2, and Rab11a form a ternary complex on the vesicle membrane.
• Spire2 and Rab11a cooperatively activate the otherwise inhibited Myo5b motor.
• This synergistic activation is the key mechanism driving long-distance vesicle transport in oocytes.