VARP binds SNX27 to promote endosomal supercomplex formation on membranes

Area of Science:

• Cell Biology
• Molecular Biology
• Biophysics

Background:

• Endosomes are central to cellular homeostasis, sorting transmembrane cargo proteins via essential membrane trafficking pathways.
• The Retromer heterotrimer interacts with Sorting Nexin (SNX) proteins, but the regulation of metazoan SNX/Retromer complexes remains unclear.

Purpose of the Study:

• To elucidate the molecular mechanisms governing the formation and regulation of metazoan SNX/Retromer complexes.
• To investigate the role of VARP in the assembly of endosomal coat complexes and membrane remodeling.

Main Methods:

• Biochemical and biophysical approaches, including AlphaFold2 Multimer modeling.
• Biochemical reconstitution assays using purified mammalian proteins and liposomes.
• Analysis of protein-protein interactions and membrane tubulation.

Main Results:

• Identified a direct interaction between the VARP N-terminus and the SNX27 PDZ domain with high affinity.
• Demonstrated that SNX27, alone or with Retromer, induces membrane tubule formation.
• Showed that VARP is essential for reconstituting a proposed endosomal "supercomplex" involving SNX27, ESCPE-1, and Retromer.

Conclusions:

• VARP acts as a key regulator in metazoans, facilitating cargo sorting from endosomes.
• The findings provide insights into the molecular basis of endosomal cargo sorting and membrane trafficking.