Human IFT-A complex structures provide molecular insights into ciliary transport

Area of Science:

• Structural Biology
• Cell Biology
• Molecular Medicine

Background:

• Intraflagellar transport (IFT) complexes (IFT-A and IFT-B) are crucial for cilia assembly and maintenance, moving along axonemal microtubules.
• Dysfunctional IFT subunits cause ciliopathies, but the precise mechanisms of IFT complex assembly and cargo transport remain unclear due to limited high-resolution structural data.

Purpose of the Study:

• To elucidate the high-resolution structure of the human IFT-A complex.
• To investigate the interaction between IFT-A and its cargo adapter TULP3.
• To understand the molecular basis of disease-causing mutations in ciliopathies.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was employed to determine the structures of human IFT-A complexes.
• Structures were resolved at resolutions ranging from 3.0 to 3.9 Å.
• Analysis included examining IFT-A in the presence and absence of TULP3, and assessing the impact of disease mutations.

Main Results:

• The cryo-EM structures reveal the 'lariat' architecture of the IFT-A complex, highlighting interconnected core and peripheral subunits stabilized by zinc-binding domains.
• TULP3 binds to IFT-A via its N-terminal region, with interface mutations shown to impair cargo transport.
• The study details the molecular effects of disease-associated mutations on IFT-A complex formation and ciliary transport dynamics.

Conclusions:

• The determined IFT-A architecture provides fundamental insights into complex assembly and ciliary transport mechanisms.
• The findings clarify the role of TULP3 as a cargo adapter and its interaction interface with IFT-A.
• This structural and mechanistic understanding enables the rationalization of various ciliopathies linked to IFT subunit mutations.