Structural Basis for the Interaction between Golgi Reassembly-stacking Protein GRASP55 and Golgin45

Area of Science:

• Cell Biology
• Structural Biology
• Biochemistry

Background:

• Golgin45 is crucial for Golgi apparatus structure and protein transport from the endoplasmic reticulum.
• The molecular mechanisms and structural role of Golgin45's interaction with GRASP55 in Golgi stacking remain largely unknown.

Purpose of the Study:

• To elucidate the molecular details and structural basis of the Golgin45-GRASP55 interaction.
• To understand the role of this complex in Golgi stacking.

Main Methods:

• X-ray crystallography was used to determine the structure of GRASP55's GRASP domains complexed with a Golgin45 C-terminal peptide at 1.33 Å resolution.
• Mutagenesis experiments were performed to validate structural observations.

Main Results:

• The crystal structure revealed simultaneous interaction with both PDZ1 and PDZ2 domains of GRASP55, involving a conserved PDZ-binding motif in Golgin45.
• Unlike the GRASP65-GM130 complex, the GRASP55-Golgin45 interaction lacks a significant structural rearrangement and specific hydrophobic interactions.
• A unique zinc finger structure was identified in the GRASP55-Golgin45 complex, with mutagenesis confirming two key sites for stable complex formation.

Conclusions:

• The GRASP55-Golgin45 interaction involves multiple binding sites and a unique structural feature, distinct from GRASP65-GM130.
• These findings provide insights into the molecular basis of Golgi stacking and protein transport.
• A novel model for Golgi stacking is proposed based on the structural data.