Emulating Membrane Protein Environments─How Much Lipid Is Required for a Native Structure: Influenza S31N M2.

Area of Science:

• Structural biology
• Biophysics
• Virology

Background:

• Influenza A virus M2 protein is a homotetrameric ion channel essential for viral replication.
• Previous studies have deposited structures of the S31N M2 protein's conductance domain, showing varied symmetries.
• Detergent environments are often non-ideal for studying small membrane proteins.

Purpose of the Study:

• To investigate the homotetrameric structure of the S31N M2 protein from Influenza A virus.
• To explore the influence of high lipid-to-protein ratios on M2 protein structure and symmetry.
• To determine the optimal lipid abundance for achieving native-like membrane protein structures.

Main Methods:

• Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy (magic angle spinning and oriented sample).
• Characterization of S31N M2 protein in liquid crystalline lipid bilayers.
• Varying protein tetramer:lipid molar ratios from 1:120 to 1:240.

Main Results:

• Spectroscopic data indicate an essentially 4-fold-symmetric structure for S31N M2 at high lipid ratios.
• The observed structure is similar to the M2 wild-type (WT) structure, with minor variations at functional sites (His37, Trp41).
• High lipid abundance, in addition to lipid type, is critical for stabilizing a native-like M2 protein conformation.

Conclusions:

• A high abundance of lipid bilayers is essential for stabilizing the native, 4-fold symmetric structure of the S31N M2 protein.
• This finding has significant implications for membrane protein structural studies, emphasizing the importance of sample preparation.
• Optimizing lipid abundance alongside lipid character is key for membrane protein spectroscopists to achieve native-like structures and maximize sensitivity.