The interplay between RPGR, PDEδ and Arl2/3 regulate the ciliary targeting of farnesylated cargo

Area of Science:

• Cell Biology
• Structural Biology
• Genetics

Background:

• Ciliopathies are human diseases caused by defects in primary cilia.
• RPGR mutations are linked to severe ciliopathies, particularly retinitis pigmentosa.
• RPGR localizes to the ciliary transition zone, a critical site for protein import.

Purpose of the Study:

• To elucidate the structural basis of RPGR function in cilia.
• To understand the interaction between RPGR and its partner PDEδ.
• To propose a model for how RPGR facilitates ciliary cargo trafficking.

Main Methods:

• X-ray crystallography to determine the structure of RPGR domains and RPGR·PDEδ complex.
• Biochemical experiments to assess binding affinities and interactions.
• Structural analysis to map mutations and conserved surfaces.

Main Results:

• The crystal structure of RPGR reveals how patient mutations affect its conformation.
• The RPGR·PDEδ complex structure shows PDEδ binding to a conserved RPGR surface.
• RPGR binds cargo-loaded PDEδ with high affinity and modulates PDEδ's Arl2/Arl3-binding site.

Conclusions:

• RPGR acts as a scaffold protein, recruiting PDEδ carrying lipidated cargo.
• This interaction facilitates the release of cargo into cilia, essential for ciliary function.
• The findings provide insights into the molecular mechanisms underlying RPGR-related ciliopathies.