Structure and Orientation of Two
Voltage-dependent Anion-selective Channel
Isoforms
AN ATTENUATED TOTAL REFLECTION FOURIER-TRANSFORM INFRARED
SPECTROSCOPY STUDY*
Helge
Abrecht
,
Erik
Goormaghtigh§¶,
Jean-Marie
Ruysschaert§, and
Fabrice
Homblé
From the Laboratoire de Physiologie
Végétale, CP 206/2, Faculté des Sciences,
Université Libre de Bruxelles, Bld du Triomphe, B-1050 Brussels,
Belgium and the § Laboratoire de Chimie Physique des
Macromolécules aux Interfaces, CP 206/2, Faculté des
Sciences, Université Libre de Bruxelles, Bld du Triomphe,
B-1050 Brussels, Belgium
Two VDAC (voltage-dependent
anion-selective channel) isoforms were purified from seed cotyledons of
Phaseolus vulgaris by chromatofocusing chromatography.
Attenuated total reflection Fourier-transform infrared (ATR-FTIR)
spectroscopy was used to study the structural properties of the two
isoforms reconstituted in a mixture of asolectin and 5% stigmasterol.
The IR spectra of the two VDAC isoforms were highly similar indicating
50 to 53% anti-parallel 
-sheet. The orientation of the -strands
relative to the barrel axis was calculated from the experimentally
obtained dichroic ratios of the amide I -sheet component and the
amide II band. Comparing the IR spectra of the reconstituted VDAC
isoforms with the IR spectra of the bacterial porin OmpF, for which a
high resolution structure is available, provided evidence for a general
structural organization of the VDAC isoforms similar to that of
bacterial porins. Hydrogen-deuterium exchange measurements indicated
that the exchange of the amide protons occurs to a higher extent in the
two VDAC isoforms than in the OmpF porin.
*
This work was supported by a grant of the 178 Communnauté Française de Belgique-Actions de Recherches
Concertées 178 and TMR Marie Curie Research Training Grant
ERBFMBICT971977 of the European Commission (to H. A.).The costs of publication of this article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
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