Proteomics Identifies Substrates and a Novel Component in hSnd2-Dependent ER Protein Targeting

Area of Science:

• Cell Biology
• Molecular Biology
• Proteomics

Background:

• Protein import into the endoplasmic reticulum (ER) is crucial for cellular function, involving specific targeting pathways.
• The signal recognition particle (SRP) and targeting to the correct channel (TRC) pathways are well-studied, but the signal-non-dependent (SND) pathway remains less understood.
• Understanding these pathways is key to deciphering protein homeostasis and cellular signaling.

Purpose of the Study:

• To identify novel components of the human SND pathway.
• To characterize the range of proteins (client spectrum) targeted by the SND pathway.
• To compare the SND pathway with the established SRP and TRC pathways.

Main Methods:

• Depletion of the hSnd2 component in HeLa cells.
• Proteomic analysis and differential protein abundance studies.
• Comparative analysis of SRP, TRC, and SND targeting pathways.

Main Results:

• TMEM109 was identified and characterized as a new component, termed hSnd3.
• The SND pathway was found to predominantly target membrane proteins.
• SND clients utilize various signal positions (N-terminal, central, C-terminal) for targeting.

Conclusions:

• The human SND pathway plays a significant role in the import of membrane proteins into the ER.
• TMEM109 (hSnd3) is a key component of the SND pathway.
• The SND pathway exhibits distinct client specificity compared to the SRP pathway.