C2 domains as protein-protein interaction modules in the ciliary transition zone

Area of Science:

• Molecular and Cellular Biology
• Structural Biology
• Genetics and Genomics

Background:

• RPGR-interacting protein 1 (RPGRIP1) mutations cause Leber congenital amaurosis (LCA).
• RPGRIP1-like (RPGRIP1L) mutations are linked to various ciliopathies.
• RPGRIP1 and RPGRIP1L are predicted to interact with RPGR, a protein implicated in X-linked retinitis pigmentosa.

Purpose of the Study:

• To elucidate the structural basis of the interaction between RPGRIP1 and RPGR.
• To investigate the functional consequences of this interaction on ciliary protein transport.
• To characterize the RPGRIP1-RPGR interaction module within the context of ciliary transition zone complexes.

Main Methods:

• X-ray crystallography was used to determine the structure of the RPGRIP1-RPGR complex.
• Structural analysis of the RPGRIP1-interacting domain (RID) of RPGRIP1.
• Biochemical assays to assess the effect of RPGRIP1 binding on PDEδ interaction.

Main Results:

• The crystal structure of the RPGRIP1-RID and RPGR complex was solved, revealing a unique C2 domain structure.
• RPGRIP1L was shown to bind RPGR in a similar manner to RPGRIP1.
• RPGRIP1 binding to RPGR modulates the interaction with PDEδ, a key factor in ciliary protein transport.
• The RPGRIP1-RID is a novel, non-calcium-binding C2 domain, suggesting a specialized role in protein-protein interactions.

Conclusions:

• The RPGRIP1-RID represents a unique, cilia-specific protein-protein interaction module.
• This module is likely integral to multiprotein complexes within the ciliary transition zone.
• Understanding this interaction provides insights into the molecular mechanisms underlying LCA and other ciliopathies.