Cryo-EM structure of an active central apparatus

Area of Science:

• Cell Biology
• Structural Biology
• Biophysics

Background:

• Ciliary beating is vital for eukaryotic cell functions, survival, and development.
• The central apparatus (CA) of motile cilia regulates beating but its structural basis is unclear.

Purpose of the Study:

• To elucidate the high-resolution structure and dynamic conformational behavior of the Chlamydomonas reinhardtii CA.
• To establish a structural framework for understanding CA's regulatory role in ciliary motility.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to determine high-resolution structures of the CA.
• Analysis of dynamic conformational states of CA components, including kinesin-like protein 1 (KLP1).

Main Results:

• Revealed clustered projection proteins on a scaffold of armadillo-repeat proteins, linked by rachis-like proteins.
• Identified elastic bridge proteins coordinating the two CA halves for synchronized activity.
• Captured KLP1 in distinct stepping states correlated with ciliary wave propagation.

Conclusions:

• The study provides a structural framework for CA function in ciliary motility.
• Detailed structures explain how CA proteins assemble and coordinate to regulate ciliary beating.
• Dynamic KLP1 states offer insights into the mechanism of ciliary wave propagation.