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Updated: Oct 4, 2025

Method to Visualize and Analyze Membrane Interacting Proteins by Transmission Electron Microscopy
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Structure of the Mon1-Ccz1 complex reveals molecular basis of membrane binding for Rab7 activation

Björn U Klink1, Eric Herrmann2, Claudia Antoni1

  • 1Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, 44227 Dortmund, Germany.

Proceedings of the National Academy of Sciences of the United States of America
|February 2, 2022
PubMed

Insights

The Mon1-Ccz1 complex structure reveals how it activates Rab7/Ypt7 GTPase, marking organelles for lysosomal fusion and degradation. This provides insight into membrane targeting and the Tri Longin domain Rab-GEF family.

Area of Science:

  • Cell Biology
  • Structural Biology
  • Molecular Mechanisms

Background:

  • Rab GTPases regulate organelle trafficking and fusion.
  • The Mon1-Ccz1 complex is a guanine nucleotide exchange factor (GEF) for Rab7/Ypt7.
  • Rab7/Ypt7 activation is crucial for endosomal and autophagosomal fusion with lysosomes/vacuoles.

Purpose of the Study:

  • To determine the high-resolution structure of the Mon1-Ccz1 complex.
  • To elucidate the molecular architecture and mechanism of Rab7/Ypt7 activation by Mon1-Ccz1.
  • To understand the membrane-targeting mechanism of the GEF.

Main Methods:

  • High-resolution cryogenic electron microscopy (cryo-EM).
  • Structural analysis of the Mon1-Ccz1 heterodimer.

Main Results:

  • Atomic-level structure of the Mon1-Ccz1 complex.
  • Mon1 and Ccz1 form a pseudo-twofold symmetrical heterodimer.
  • Triangular arrangement of Longin domains forms a scaffold for the catalytic center.
  • A phosphatidylinositol phosphate-binding site on Mon1 explains membrane targeting.

Conclusions:

  • The structure provides molecular insight into endosomal Rab activation.
  • The findings reveal the mechanism of GEF-mediated organelle fusion.
  • This work serves as a blueprint for understanding Tri Longin domain Rab-GEF family functions.
Keywords:
GEFGTPasecryo-EMendosometrafficking

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