Structural basis for activation of Arf1 at the Golgi complex

Area of Science:

• Cell Biology
• Molecular Biology
• Structural Biology

Background:

• The Golgi complex is a key organelle in eukaryotic cells, responsible for protein modification and sorting within the secretory pathway.
• Activation of Arf guanosine triphosphatases (Arfs) is essential for cargo sorting and vesicle formation at the Golgi.
• Large guanine nucleotide exchange factors (GEFs) regulate Arf activation and membrane association through their conserved domains.

Purpose of the Study:

• To determine the structural organization of the full-length yeast Arf-GEF, Gea2, a paralog of human GBF1.
• To elucidate the mechanism by which Gea2 binds to the Golgi membrane.
• To understand how Gea2's conformational changes facilitate Arf1 activation and membrane insertion.

Main Methods:

• Cryoelectron microscopy (cryoEM) was used to obtain high-resolution structures of full-length Gea2.
• Structures of Gea2 alone and in complex with Arf1 were determined.
• Analysis of domain organization and conformational states of Gea2.

Main Results:

• CryoEM structures revealed the organization of Gea2's regulatory domains and its Golgi membrane binding mode.
• The GEF domain of Gea2 exists in two conformations, suitable for different Arf activation stages.
• An intermediate structure of Gea2-Arf1 suggests a mechanism for priming Arf1 for membrane insertion.

Conclusions:

• Conformational switching of Gea2 during nucleotide exchange is critical for promoting Arf1 membrane insertion.
• These findings provide structural insights into the regulation of Arf proteins at the Golgi.
• The study clarifies the role of Gea2 in orchestrating protein transport within the secretory pathway.