Fig. 6: Proposed Molecular Mechanism of MICAL1 Autoinhibition and Activation.

Initially, MICAL1 activity is autoinhibited by an intramolecular interaction between the MO domain and the CCα1^inh helix. This interaction sterically hinders F-actin from binding to the MO domain. A crucial component of this autoinhibitory mechanism is the tripartite CH-L2α1-LIM complex, which interacts with the CC^inh domain to maintain a CC conformation that facilitates the CCα1 helix’s binding to the MO domain. The binding of Rab10 to MICAL1 initiates the dissociation of the CH-L2α1-LIM complex, leading to the straightening or axial adjustment of the CCα3 helix. This triggers an allosteric change in the CCα1^inh helix, causing its proximal portion to shift away from the MO domain. While it remains uncertain whether this results in a complete or partial dissociation of the CC domain from the MO domain, this conformational shift likely exposes the F-actin binding site. Additionally, the conformation of the Rab-bound CC^act domain may be further stabilized by a second Rab molecule, enhancing the activation process.