A novel mammalian retromer component, Vps26B.

Area of Science:

• Cell Biology
• Molecular Biology
• Genomics

Background:

• The retromer complex is crucial for endosomal trafficking in mammalian cells.
• It comprises Vps26, Vps29, and Vps35 proteins, along with sorting nexins.
• Its role in receptor and ligand transport within the endosomal/lysosomal system is well-established.

Purpose of the Study:

• To identify and characterize novel components of the mammalian retromer complex.
• To investigate the evolutionary origins and cellular localization of retromer paralogs.
• To determine the subunit composition and membrane association of the newly identified Vps26B protein.

Main Methods:

• Bioinformatic analysis of the mouse genome to identify retromer paralogs.
• Phylogenetic studies to trace evolutionary history.
• Biochemical characterization including co-precipitation and yeast two-hybrid assays.
• Cellular localization studies using immunofluorescence microscopy in HeLa, A549, and HEK293 cells.
• Total internal reflection fluorescence microscopy to confirm plasma membrane association.

Main Results:

• A new Vps26 paralog, Vps26B, was identified in the mouse genome.
• Phylogenetic analysis suggests Vps26 paralogs evolved after chordates.
• Vps26B is a peripheral membrane protein that directly interacts with Vps35, confirming its role as a retromer subunit.
• Vps26B localizes to the cytoplasm and plasma membrane in HeLa cells, and to actin-rich lamellipodia in A549 cells.
• Vps26A predominantly localizes to endosomal membranes, while both Vps26A and Vps26B associate with the plasma membrane in some cell types.

Conclusions:

• The mammalian retromer complex consists of at least two Vps26 paralogs, Vps26A and Vps26B.
• Vps26B is a functional subunit of the retromer complex.
• Mammalian retromer complexes can be located at both endosomes and the plasma membrane, depending on the cell type.
• The discovery of Vps26B expands our understanding of retromer diversity and function in chordates.