Brugia Malayi - Clark Science Center - Smith College

Ion Transport of Extruded Liposomes as Cell Membranes
Esther Hong
Phospholipids are a type of lipids containing a hydrophilic polar head and hydrophobic tails. Phospholipids are important because
they can be found in biological membranes. These lipids create a barrier for the passage of hydrophilic material, such as water and
ions. In the presence of water, lipids form vesicles, or liposomes, which act as model cell membranes. This summer I examined a
set of novel synthesized cyclic peptides and their ionophoric activity. 1 These cyclic peptides can form a flat ring structure that can
stack to form dimers. I studied the ion transport of these cyclic peptides by preparing liposomes and examining the mediated ion
transport using 23 Na Nuclear Magnetic Resonance (NMR).
When first hydrated, most lipids form multilayered liposomes. I used extrusion to convert these mulilamellar structures into
unilamellar, or bilayer, systems to model cell membranes found in nature. Ion channels and transporters facilitate the transport of
material and signals in and out of the cell. These regulate the flow of metal ions across cellular lipid bilayers. Cyclic peptides were
then added to these liposomes in varying amounts and tested using NMR.
I used the prepared liposomes to test ionophores, including various cyclopeptides that can stack to form dimer ionophores
and gramicidin, a known ion transporter as a standard by which to judge the efficiency of the cyclic peptides. 1 I compared
changes over time in NMR peaks that indicate the concentration of ions in and out of the liposomes 2 . Increasing intracellular ion
concentration indicates that the ionophore is effectively transporting ions from the higher extracellular concentration to the lower
intracellular concentration. Initial tests show immediate concentration changes that plateau over time, suggesting that the tested
cyclic peptides have an ion channel-like mechanism. 3
Discovering new compounds that have the ability to transport ions across cell membranes well can aid in the medical field,
helping form new antibiotics that can have a faster effect on the human body. Determining if the tested cyclic peptides can be
used as ion channels can lead us in a direction to possibly implement them for use in the future. I have presented my research to
fellow students and will continue with my project in the fall. (Supported by the Howard Hughes Medical Institute)
Advisor: Cristina Suarez
References:
1 Amorin M., Castedo, Luis., Granja, J.R. (2008) Folding Control in Cyclic Peptides through N-Methylation Pattern Selection: Formation of Antiparallel β-Sheet
Dimers, Double Reverse Turns and Supramolecular Helices by 3α,γ Cyclic Peptides. Chem.Eur.J. 14:2100.
2 Jin, T.; Kinjo, M.; Koyama, T.; Kobayashi, Y.; Hirata, H. Langmuir (1996) Selective Na + Transport through Phospholipid Bilayer Membrane by a Synthetic Calix[4]
arene Carrier, 12: 2684-2689.
3 Herasymova, N. (2010) Gramicidin A and Cyclic Peptide Channel Conductances in Black Lipid Membranes. (Honors Thesis, Smith College, 2010).
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