Swapping mutants of voltage dependent anion channel highlight the functional importance of the N-terminal and confers anti-ageing features to the cell

Voltage-dependent anion channels (VDACs) are the most abundant proteins of the mitochondrial outer membrane that form hydrophilic pore structures. VDAC constitutes the main pathway through which metabolites are exchanged between the cytosol and mitochondria and also serves as a site for the docking of cytosolic proteins, such as hexokinase. The structure of mammalian VDAC1 has been recently solved by NMR and crystallization experiments [1]. It shows a rather compact transmembrane channel, formed by 19 amphipathic β strands connected by short turns and loops, with the striking addition of the N-terminal moiety structured with α-helix segments. The N- terminal sequence is located inside the channel, forming a partial obstruction of the wide pore. CD and NMR spectroscopy showed that the 20 aa N-terminal peptide needs a special environment to form an ordered α-helix secondary structure. In addition it was shown that the deletion of the N-terminal does not change the mitochondrial targeting of the protein [2]. In higher eukaryotes three VDAC isoforms exist, but only VDAC1 and VDAC2 are well characterized. On the contrary VDAC3 has been poorly studied and does not show an evident pore-forming ability [3]. In this work, we provide insight into the function of the isoform 3 by exchanging the N-terminal sequence of the human VDAC3 with the homologous sequences of human VDAC1 and VDAC2. The activity of the wild type and chimeric proteins was monitored in Δpor1 yeast strain. Results obtained in complementation assay, oxidative stress resistance, chronological aging, ROS production and mitochondrial membrane activity measurements, outline the importance of the N-terminal moiety of VDAC isoforms in the function of the protein. Surprisingly swapping mutants show a doubled lifespan in comparison with wild type yeast strains.