Biomedical subjects

Vitali Borisenko

Publications and source records attributed to Vitali Borisenko.

5 recordsLinked to original sources

PubMed2004

Photomodulation of ionic current through hemithioindigo-modified gramicidin channels.

Incorporation of photo-switchable amino acids into peptides and proteins offers prospects for the control of complex biochemical processes using light. Currently, only a few photo-switchable amino acids are known. We report the design and synthesis of a novel hemithioindigo-based amino acid and its incorporation into the model ion channel gramicidin. Photoisomerization of the hemithioindigo moiety between E and Z isomeric forms is shown to modulate ionic current through the channel in a predictable way. This new amino acid thus expands the possibilities for photo-control in diverse systems.

Anti-Bacterial Agents↗

PubMed2004

Engineering charge selectivity in model ion channels.

Most ion channel proteins exhibit some degree of charge selectivity, that is, an ability to conduct ions of one charge more efficiently than ions of the opposite charge. The structural origins of charge selectivity remain incompletely understood despite recent advances in the determination of cation-selective and anion-selective channel protein structures. Helix bundle channels formed via self-assembly of the peptide alamethicin provide a tractable model system for exploring the structural basis of charge selectivity. We synthesized covalently-linked alamethicin dimers, with amino acid substitutions at position 18 [lysine (Lys), arginine (Arg), glutamine (Gln), 2,3-diaminopropionic acid (Dpr)] in each helix, to assess the role of this position as a charge-selectivity determinant in alamethicin channels. Of the position 18 substitutions investigated, the Lys derivative exhibited the greatest degree of anion selectivity. Arg-containing channels were slightly less anion-selective than Lys. Interestingly, Dpr channels showed cation selectivity nearly equivalent to that exhibited by the neutral Gln derivative. We suggest that this result is due to a wider pore diameter that permits a greater number of counter-ions leading to enhanced charge screening and a lower effective side-chain positive charge.

Alamethicin↗

PubMed2003

Understanding pH-dependent selectivity of alamethicin K18 channels by computer simulation.

Alamethicin K18 is a covalently linked alamethicin dimer in which the glutamine residue at position 18 in each helix has been replaced by a lysine residue. As described in previous work, channels formed by this peptide show pH-dependent selectivity. The maximum anion selectivity of the putative octameric conducting state is obtained at pH 7 or lower. Inasmuch as no change in selectivity is seen between pH 7 and pH 3, and because protons are expected to be in equilibrium with the open state of the channel during a selectivity measurement, the channel is believed to be fully charged (i.e., all eight lysines protonated) at pH 7. In an effort to understand how such a highly charged channel structure is stable in membranes and why it is not more selective for anions, we have performed a number of computer simulations of the system. Molecular dynamics simulations of 10 ns each of the octameric bundle in a lipid bilayer environment are presented, with either zero, four, or eight lysines charged in the absence of salt, and with eight lysines charged in the presence of 0.5 M and 1 M KCl. When no salt is present and all lysines are charged, on average 1.9 Cl(-) ions are inside the channel and the channel significantly deforms. With 0.5 M KCl present, 2.9 Cl(-) ions are inside the channel. With 1 M KCl present, four Cl(-) ions are present and the channel maintains a regular structure. Poisson-Boltzmann calculations on models of the octameric channel also predict an average of 2-4 Cl(-) ions near the lysine residues as a function of ionic strength. These counterions lower the apparent charge of the channel, which may underlie the decrease in selectivity observed experimentally with increasing salt concentrations. We suggest that to increase the selectivity of Alm K18 channels, positive charges could be engineered in a narrower part of the channel.

Alamethicin↗

PubMed2002

Gramicidin derivatives as membrane-based pH sensors.

Ion channels provide a means for sensitive pH measurement at membrane interfaces. Detailed knowledge of the structure and function of gramicidin channels permits the engineering of pH-sensitive derivatives. Two derivatives, gramicidin-ethylenediamine and gramicidin-histamine, are shown to exhibit pH-dependent single-channel behaviour over the pH ranges 9-11 and 6.5-8.5, respectively. Thermal isomerization of a carbamate group at the entrance of the channels leads to a pattern of steps in single-channel recordings. The size of the steps depends on the time-averaged degree of protonation of the appended group (ethylenediamine or histamine). Measurement of the size of the steps thus permits single-molecule pH sensing under symmetrical pH conditions or in the presence of a pH gradient.

Biosensing Techniques↗

PubMed2002

Polyanions decelerate the kinetics of positively charged gramicidin channels as shown by sensitized photoinactivation.

The effects of different anionic polymers on the kinetic properties of ionic channels formed by neutral gramicidin A (gA) and its positively charged analogs gramicidin-tris(2-aminoethyl)amine (gram-TAEA) and gramicidin-ethylenediamine (gram-EDA) in a bilayer lipid membrane were studied using a method of sensitized photoinactivation. The addition of Konig's polyanion caused substantial deceleration of the photoinactivation kinetics of gram-TAEA channels, which expose three positive charges to the aqueous phase at both sides of the membrane. In contrast, channels formed of gram-EDA, which exposes one positive charge, and neutral gA channels were insensitive to Konig's polyanion. The effect strongly depended on the nature of the polyanion added, namely: DNA, RNA, polyacrylic acid, and polyglutamic acid were inactive, whereas modified polyacrylic acid induced deceleration of the channel kinetics at high concentrations. In addition, DNA was able to prevent the action of Konig's polyanion. In single-channel experiments, the addition of Konig's polyanion resulted in the appearance of long-lived gram-TAEA channels. The deceleration of the gram-TAEA channel kinetics was ascribed to electrostatic interaction of the polyanion with gram-TAEA that reduces the mobility of gram-TAEA monomers and dimers in the membrane via clustering of channels.

Acrylic Resins↗