Browsing by Author "Roark, Torri C."

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    Cation-selective channel is regulated by anions according to their Hofmeister ranking
    (Wiley, 2017-03-20) Gurnev, Philip A.; Roark, Torri C.; Petrache, Horia I.; Sodt, Alexander J.; Bezrukov, Sergey M.; Physics, School of Science
    Specificity of small ions, the Hofmeister ranking, is long-known and has many applications including medicine. Yet it evades consistent theoretical description. Here we study the effect of Hofmeister anions on gramicidin A channels in lipid membranes. Counterintuitively, we find that conductance of this perfectly cation-selective channel increases about two-fold in the H2PO4−
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    Conductance of Ideally Cation Selective Channel Depends on Anion Type
    (Office of the Vice Chancellor for Research, 2013-04-05) Roark, Torri C.; Gurnev, Philip A.; Petrache, Horia I.; Bezrukov, Sergey M.
    Gramicidin A (gA) is a transmembrane, cation selective ion channel that has been used in many biophysical studies of lipid bilayers, in particular for investigations of lipid-protein interactions and membrane electrostatics. In addition, it was found that ionic interactions with neutral lipid membranes also affect the kinetics of gA channels. Here we report measurements of gA ion-channels for a series of sodium and potassium salts that show an anion-dependence of gA conductance. We find that gA conductance varies significantly with the anion type with ClO4 and SCN producing distinctly larger conductance values than Cl, F, and H2PO4. These results can provide new insights into ion-lipid membrane interactions and ion channel functions in general.
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    Correlations of Specific Ionic Effects using Ion Channels and Surface Charge Measurements
    (Office of the Vice Chancellor for Research, 2014-04-11) Roark, Torri C.; Hermida, Oscar Teijido; Rostovtseva, Tatiana K.; Gurnev, Philip A.; Petrache, Horia I.; Bezrukov, Sergey M.
    Specific ionic effects, as captured in the Hofmeister series, have been observed in many biological phenomena including protein folding and aggregation and lipid bilayer interactions. Previously we have shown that the Hofmeister effect is present in the activity of gramicidin A channels. In particular, measurements of channel open lifetime and conductance in potassium salts clearly show the existence of two distinct ionic classes that could be identified as kosmotropic and chaotropic. To further investigate this behavior, we have measured the zeta potential of diphytanoyl phosphatidylcholine (DPhPC) liposomes in salt solutions. We observe that anions alter the surface charge of the liposomes depending on the classification of the anion as kosmotropic or chaotropic. Chaotropic anions (SCN-, ClO4-) decrease the surface charge of the liposomes while kosmotropic anions (Cl-, H2PO4-, SO42-) have the opposite effect. These results correlate with our previous studies of cation conductance through gramicidin A channels adding new insight into ionic interactions at the lipid-water interface.