CHANNELS, RECEPTORS, AND ELECTRICAL SIGNALING |
Phosphorothioate Oligonucleotides Block the VDAC Channel
Wenzhi Tan 1, Yue-Hin Loke 1, C. A. Stein 2, Paul Miller 3 and Marco Colombini 1*
1 Univ. of Maryland
2 Albert Einstein-Montefiore Cancer Center
3 Johns Hopkins Univ.
* To whom correspondence should be addressed. E-mail: colombin{at}umd.edu.
Submitted on January 26, 2007
Revised on February 19, 2007
Accepted on 26 April 2007
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Abstract |
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Pro-apoptotic phosphorothioate oligonucleotides, such as G3139 (an 18-mer), induce Bcl-2 independent apoptosis, perhaps partly due to direct interaction with VDAC and reduction of metabolite flow across the mitochondrial outer membrane. Here, we analyzed the interactions at the molecular level. Ten micromolar G3139 induces rapid flickering of the VDAC conductance and, occasionally, a complete conductance drop. These phenomena only occur when VDAC is in the "open" conformation and therefore are consistent with pore blockage rather than VDAC closure. Blockage occurs preferentially from one side of the VDAC channel. It depends linearly on the [G3139] and is voltage-dependent with an effective valence of -3. The kinetics indicate at least a partial entry of G3139 into VDAC, forming an unstable bound state, which is responsible for the rapid flickering (~0.1 ms). Subsequently, a long-lived blocked state is formed. An 8-mer phosphorothioate, poly-deoxythymidine induces partial blockage of VDAC and a change in selectivity from favoring anions to favoring cations. Thus the oligonucleotide is close to the ion stream. The phosphodiester congener of G3139 is ineffective at the concentrations used, excluding a general polyanion effect. This shows the importance of sulfur atoms. The results are consistent with a binding-induced blockage rather than a permeation block.
Key Words:
G3139, blocker, flicker, membrane, nucleotide, voltage-dependent
