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Download fileSingle-Particle Tracking Reveals Switching of the HIV Fusion Peptide between Two Diffusive Modes in Membranes
journal contribution
posted on 2013-10-24, 00:00 authored by Maria Ott, Yechiel Shai, Gilad HaranFusion of the HIV membrane with that
of a target T cell is an essential first step in the viral infection
process. Here we describe single-particle tracking (SPT) studies of
a 16-amino-acid peptide derived from the HIV fusion protein (FP16), as it interacts with a supported lipid bilayer. FP16 was found to spontaneously insert into and move within the
bilayer with two different modes of diffusion, a fast mode with a
diffusion coefficient typical of protein motion in membranes and a
much slower one. We observed transitions between the two modes: slow
peptides were found to speed up, and fast peptides could slow down.
Hidden Markov model analysis was employed as a method for the identification
of the two modes in single-molecule trajectories and analysis of their
interconversion rates. Surprisingly, the diffusion coefficients of
the two modes were found to depend differently on solution viscosity.
Thus, whereas the fast diffusive mode behaved as predicted by the
Saffman–Delbrück theory, the slow mode behaved according
to the Stokes–Einstein relation. To further characterize the
two diffusive modes, FP16 molecules were studied in bilayers
cooled through their liquid crystalline-to-gel phase transition. Our
analysis suggested that the slow diffusive mode might originate from
the formation of large objects, such as lipid domains or local protrusions, which are induced
by the peptides and move together with them.