Abstract
The plasma membrane (PM) contains an asymmetric distribution of lipids between the inner and outer bilayer leaflets. A lipid of special interest in eukaryotic membranes is the negatively charged phosphatidylserine (PS). In healthy cells, PS is actively sequestered to the inner leaflet of the PM, but PS redistributes to the outer leaflet when the cell is damaged or at the onset of apoptosis. However, the influence of PS asymmetry on membrane protein structure and folding are poorly understood. The pH low insertion peptide (pHLIP) adsorbs to the membrane surface at a neutral pH, but it inserts into the membrane at an acidic pH. We have previously observed that in symmetric vesicles, PS affects the membrane insertion of pHLIP by lowering the pH midpoint of insertion. Here, we studied the effect of PS asymmetry on the membrane interaction of pHLIP. We developed a modified protocol to create asymmetric vesicles containing PS and employed Annexin V labeled with an Alexa Fluor 568 fluorophore as a new probe to quantify PS asymmetry. We observed that the membrane insertion of pHLIP was promoted by the asymmetric distribution of negatively charged PS, which causes a surface charge difference between bilayer leaflets. Our results indicate that lipid asymmetry can modulate the formation of an α-helix on the membrane. A corollary is that model studies using symmetric bilayers to mimic the PM may fail to capture important aspects of protein-membrane interactions.
Original language | English |
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Pages (from-to) | 1495-1506 |
Number of pages | 12 |
Journal | Biophysical Journal |
Volume | 116 |
Issue number | 8 |
DOIs | |
State | Published - Apr 23 2019 |
Funding
This work was partially supported by grant R01GM120642 from the National Institutes of Health (F.N.B.), National Science Foundation grant number MCB-1817929 (F.A.H.), and by funds from the University of Tennessee Oak Ridge National Laboratory Joint Institute for Biological Sciences to F.N.B. Support was also received from the University of Tennessee Oak Ridge National Laboratory Science Alliance in the form of a Joint Directed Research and Development Award (to F.N.B.). aLUV preparation, GC/MS, and DLS measurements were supported by the Biophysical Characterization Laboratory suite of the Shull Wollan Center at Oak Ridge National Laboratory . J.K. is supported through the Scientific User Facilities Division of the Department of Energy Office of Science, sponsored by the Basic Energy Science Program, Department of Energy Office of Science, under contract number DEAC05-00OR22725 .
Funders | Funder number |
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Basic Energy Science Program | DEAC05-00OR22725 |
Department of Energy Office of Science | |
University of Tennessee Oak Ridge National Laboratory Joint Institute for Biological Sciences | |
National Science Foundation | MCB-1817929 |
National Science Foundation | |
National Institutes of Health | |
National Institute of General Medical Sciences | R01GM120642 |
National Institute of General Medical Sciences | |
Oak Ridge National Laboratory |