posted on 2022-01-28, 17:35authored byAnna K. Wright, Joana Paulino, Timothy A. Cross
This
report investigates the homotetrameric membrane protein structure
of the S31N M2 protein from Influenza A virus in the presence of a
high molar ratio of lipid. The structured regions of this protein
include a single transmembrane helix and an amphipathic helix. Two
structures of the S31N M2 conductance domain from Influenza A virus
have been deposited in the Protein Data Bank (PDB). These structures
present different symmetries about the channel main axis. We present
new magic angle spinning and oriented sample solid-state NMR spectroscopic
data for S31N M2 in liquid crystalline lipid bilayers using protein
tetramer:lipid molar ratios ranging from 1:120 to 1:240. The data
is consistent with an essentially 4-fold-symmetric structure very
similar to the M2 WT structure that also has a single conformation
for the four monomers, except at the His37 and Trp41 functional sites
when characterized in samples with a high molar ratio of lipid. While
detergent solubilization is well recognized today as a nonideal environment
for small membrane proteins, here we discuss the influence of a high
lipid to protein ratio for samples of the S31N M2 protein to stabilize
an essentially 4-fold-symmetric conformation of the M2 membrane protein.
While it is generally accepted that the chemical and physical properties
of the native environment of membrane proteins needs to be reproduced
judiciously to achieve the native protein structure, here we show
that not only the character of the emulated membrane environment is
important but also the abundance of the environment is important for
achieving the native structure. This is a critical finding as a membrane
protein spectroscopist’s goal is always to generate a sample
with the highest possible protein sensitivity while obtaining spectra
of the native-like structure.