Voltage dependent anion channel VDAC in plant mitochondria
VDAC (Voltage-Dependent Anion-selective Channel) is the major pathway for solutes exchange across the mitochondrial outer membrane. It participates to cell life (energy production, metabolism) and death (apoptosis, necrosis) processes. We are studying the structure, function and regulation of VDAC.
Our main achievements are:
a) development of protocols for protein purification and isoform separation
b) structural characterizations notably the first experimental determination of the
β-strand tilt angle
c) gene cloning and expression
d) channel regulation by membrane phytosterols
Pore and channel forming polypeptides
Several polypeptides are known to insert in or to interact with the lipid bilayer and to modify its ion permeability. Electrophysiology was used to show that Yop B and D of Yersinia enterocolitica form the translocation pore of type III secretion-translocation system, the human ApoL-I promotes trypanosome lysis by forming a chloride channel, the cell-penetrating peptide pep-1 and the antibacterial PR-39 peptides alter the bilayer permeability.
Nonlinear dynamics of ion transport through cells
Apical growth is a typical feature of plants and fungi. It is correlated to the emergence of pattern of transcellular ion currents. In collaboration with Marc Léonetti (IRPHE, France) we have proposed a simple electrodiffusion model that accounts for the observed experimental results. Our main achievements are:
a) development of a simple (two types of channels) model to explain the emergence of transcellular ion current patterns and symmetry breaking at the early stage of plant zygote growth and development
b) generalization of the model to the coupling between other membrane transporters (e.g., ATPase/cotransporter)
c) analysis of the channel self-aggregation theory. Beyond the weak non linear analysis, we determine analytically and numerically four secondary instabilities and notably, a parity-breaking instability and a global oscillation of ionic channel density. In the subcritical case, the drift instability can be used to transfer some information along cells. These results might explain the lability of the dipolar transcellular ionic currents in the Fucus.