The membrane binding and deformation property of vaccinia virus K1 ankyrin repeat domain protein

Membrane lipids are essential participants in cellular events, but only a small number of lipid-interacting proteins have been characterized. Taking advantage of the small genome (~270 genes) of the vaccinia virus, we screened for soluble lipid-binding proteins and found 27 proteins to be soluble after expression in Escherichia coli. Among them, 4 proteins were found to strongly bind to the total bovine brain lipid extract (Folch I fraction) that contained large amounts of phosphatidylserine in vitro. Out of the 4 proteins, 3 were unique proteins to viruses. Another protein, K1, solely contained an ankyrin repeat domain (ARD). ARD is conserved in large numbers of proteins in bacteria, archaea, eukaryotes and viruses, suggesting the possibilities of the membrane binding of ARDs in varieties of proteins. Furthermore, K1 deformed the lipid membrane dependently on the charged lipids. The tubulation and membrane binding was enhanced with increased negative membrane charge from phosphatidylinositol 4,5-bisphosphate (PI(4,5)P₂ ). The basic amino acid residues in the ARD were essential for membrane deformation, suggesting electrostatic interactions between K1 and the membrane for membrane deformation.