The DC-module of doublecortin: dynamics, domain boundaries, and functional implications

Area of Science:

• Structural biology
• Neuroscience
• Biochemistry

Background:

• Doublecortin-like (DC) domains are novel microtubule-binding modules.
• DC domains are found in proteins like doublecortin (DCX) and doublecortin-like kinase (DCLK), implicated in neuronal migration and other functions.
• Mutations in proteins containing DC domains, such as the RP1 gene product, can cause inherited blindness.

Purpose of the Study:

• To investigate the structural dynamics of the N-terminal doublecortin domain of human doublecortin (N-DCX).
• To understand the functional implications of conformational changes in DC domains for microtubule binding and function.

Main Methods:

• X-ray crystallography was used to determine the structure of a mutant N-DCX protein.
• Heteronuclear Nuclear Magnetic Resonance (NMR) spectroscopy was employed to study the domain's conformation in solution.

Main Results:

• An X-ray structure revealed an unexpected "open" conformation of the C-terminal fragment of N-DCX.
• NMR data indicated that this "open" conformation is transient in solution, with the domain predominantly adopting a "closed" conformation.
• The conformational switching alters the linker length between tandem DC domains, suggesting a regulatory mechanism.

Conclusions:

• The dynamic switching between "open" and "closed" conformations of DC domains is likely functionally significant.
• This conformational flexibility may play a role in regulating tubulin polymerization and microtubule bundling by doublecortin.
• Crystal packing may stabilize the observed "open" conformation, but the solution dynamics are key to function.