1 research outputs found
Microscopic Rates of Peptide–Phospholipid Bilayer Interactions from Single-Molecule Residence Times
The binding of glucagon-like peptide-1 (GLP-1) to a planar
phospholipid
bilayer is measured using single-molecule total internal reflection
fluorescence microscopy. From several reports in the literature, GLP-1
has been shown to be a random coil in free solution, adopting a folded,
α-helix conformation when intercalated into membrane environments.
Single-molecule fluorescence measurements of GLP-1 binding to supported
lipid bilayers show evidence of two populations of membrane-associated
molecules having different residence times, suggesting weakly adsorbed
peptides and strongly bound peptides in the lipid bilayer. The path
to and from a strongly bound (folded, intercalated) state would likely
include an adsorbed state as an intermediate, so that the resulting
kinetics would correspond to a consecutive first-order reversible
three-state model. In this work, the relationships between measured
single-molecule residence times and the microscopic rates in a three-state
kinetic model are derived and used to interpret the binding of GLP-1
to a supported lipid bilayer. The system of differential equations
associated with the proposed consecutive-three state kinetics scheme
is solved, and the solution is applied to interpret histograms of
single-molecule, GLP-1 residence times in terms of the microscopic
rates in the sequential two-step model. These microscopic rates are
used to estimate the free energy barrier to adsorption, the fraction
of peptides adsorbing to the membrane surface that successfully intercalate
in the bilayer, the lifetime of inserted peptides in the membrane,
and the free energy change of insertion into the lipid bilayer from
the adsorbed state. The transition from a random coil in solution
to a folded state in a membrane has been recognized as a common motif
for insertion of membrane active peptides. Therefore, the relationships
developed here could have wide application to the kinetic analysis
of peptide–membrane interactions