Phosphate Ions Promoting Association between Peptide
and Modeling Cell Membrane Revealed by Sum Frequency Generation Vibrational
Spectroscopy
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Abstract
Phosphate
ion is one of the most important anions present in the intracellular
and extracellular fluid. It can form strongly hydrogen-bonded and
salt-bridged complexes with arginine and lysine to activate the voltage
gated channel protein. A molecular-level insight into how the phosphate
anions mediate the interaction between peptides and cell membrane
is critical to understand membrane-bound peptide actions. In this
study, sum frequency generation vibrational spectroscopy (SFG-VS)
has been applied to characterize interactions between mastoparan (MP,
a G-protein-activating peptide) and different charged lipid bilayers
in situ. It is found that phosphate ions can greatly promote the association
of MP with lipid bilayers and accelerate the conformation transition
of membrane-bound MP from aggregation into α-helical structure.
In phosphate buffer solution, MP can insert not only into negatively
and neutrally charged lipid bilayers but also into positively charged
lipid bilayers. In neutrally and negatively charged lipid bilayers,
the tilt angle of α-helical structure becomes smaller with increasing
buffer concentration, while MP adopts a multiple orientation distribution
in the positively charged lipid bilayer. MP interacts with lipid bilayers
in the salt solution environment most likely by formation of toroidal
pores inside the bilayer matrix. Results from our studies will provide
insight into the MP action mechanism and offer some ideas to deliver
exogenous protein into the cytosol