Immobilization
of Phosphatidylinositides Revealed
by Bilayer Leaflet Decoupling
Posted on 2020-07-20 - 21:29
Phosphatidylinositol 4,5-bisphosphate
(PIP2) has a significantly
lower mobile fraction than most other lipids in supported lipid bilayers
(SLBs). Moreover, the fraction of mobile PIP2 continuously
decreases with time. To explore this, a bilayer unzipping technique
was designed to uncouple the two leaflets of the SLB. The results
demonstrate that PIP2 molecules in the top leaflet are
fully mobile, while the PIP2 molecules in the lower leaflet
are immobilized on the oxide support. Over time, mobile PIP2 species flip from the top leaflet to the bottom leaflet and become
trapped. It was found that PIP2 flipped between the leaflets
through a defect-mediated process. The flipping could be completely
inhibited when holes in the bilayer were backfilled with bovine serum
albumin (BSA). Moreover, by switching from H2O to D2O, it was shown that the primary interaction between PIP2 and the underlying substrate was due to hydrogen bond formation,
which outcompeted electrostatic repulsion. Using substrates with fewer
surface silanol groups, like oxidized polydimethylsiloxane, led to
a large increase in the mobile fraction of PIP2. Moreover,
PIP2 immobilization also occurred when the bilayer was
supported on a protein surface rather than glass. These results may
help to explain the behavior of PIP2 on the inner leaflet
of the plasma membrane, where it is involved in attaching the membrane
to the underlying cytoskeleton.
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Sun, Simou; Liu, Chang; Rodriguez Melendez, Danixa; Yang, Tinglu; Cremer, Paul S. (2020). Immobilization
of Phosphatidylinositides Revealed
by Bilayer Leaflet Decoupling. ACS Publications. Collection. https://doi.org/10.1021/jacs.0c03800