Structural and mechanistic insights into the interaction between Rho and mammalian Dia.

Area of Science:

• Cell Biology
• Structural Biology
• Biochemistry

Background:

• Formins are key regulators of the actin cytoskeleton, essential for cellular processes.
• Diaphanous-related formins (DRFs) possess an N-terminal Rho GTPase-binding domain (GBD) and FH3 domain, interacting with the C-terminal Diaphanous autoregulatory domain (DAD) to maintain inactivity.
• Activation by Rho proteins releases the DAD, enabling formin-mediated actin nucleation and elongation.

Purpose of the Study:

• To elucidate the structural basis of Diaphanous-related formin regulation by Rho GTPases.
• To present the crystal structure of RhoC in complex with the N-terminal regulatory region of mammalian Diaphanous 1 (mDia1).

Main Methods:

• X-ray crystallography was used to determine the structure of the RhoC-mDia1 N-terminal complex.
• Biochemical assays were employed to identify binding sites and assess interactions.

Main Results:

• The crystal structure reveals RhoC interacting with two subdomains of the mDia1 GBD/FH3 region via its switch regions.
• The FH3 domain of mDia1 forms a stable dimer.
• The DAD-binding site was identified, and it was shown that Rho and DAD binding to the mDia1 N-terminal fragment are mutually exclusive but have partially overlapping binding sites.

Conclusions:

• A structural model for the Rho- and DAD-mediated regulation of mDia1 is proposed.
• Understanding these interactions provides insight into the precise control of actin dynamics by formins.