Proteomic Analysis Identifies Membrane Proteins Dependent on the ER Membrane Protein Complex.

Area of Science:

• Cell Biology
• Molecular Biology
• Proteomics

Background:

• The Endoplasmic Reticulum (ER) Membrane Protein Complex (EMC) is crucial for biogenesis and membrane integration of transmembrane proteins.
• The precise mechanisms and full range of EMC-dependent proteins are not well understood.

Purpose of the Study:

• To identify EMC-dependent and independent membrane proteins using unbiased quantitative proteomics.
• To elucidate the structural features of transmembrane domains (TMDs) that confer EMC dependency.
• To expand the validated list of proteins affected by EMC function.

Main Methods:

• Quantitative proteomic analysis using mass spectrometry (MS) comparing EMC-deficient and wild-type (WT) cells.
• Identification and validation of EMC-dependent and independent membrane proteins.
• Mutagenesis studies to investigate the role of polar/charged residues in TMDs on EMC dependency.

Main Results:

• Identified 36 EMC-dependent and 171 EMC-independent membrane proteins.
• Validated six EMC-dependent and six EMC-independent proteins.
• Discovered that EMC-dependent proteins commonly possess TMDs with polar and/or charged residues.
• Demonstrated that altering polar/charged residues in TMDs can switch EMC dependency.

Conclusions:

• The EMC plays a significant role in integrating transmembrane proteins with challenging TMDs.
• The presence of polar/charged residues within TMDs is a key determinant of EMC dependency.
• This work provides a more comprehensive understanding of EMC function in protein biogenesis.