N-terminal α-helix-independent membrane interactions facilitate adenovirus protein VI induction of membrane tubule formation.

Adenovirus disrupts endosomal membranes during cell entry. The membrane lytic capsid protein VI (pVI) facilitates entry by fragmenting membranes. Although an N-terminal amphipathic α-helix (VI-Φ) possesses similar membrane affinity as pVI, truncated protein lacking VI-Φ (VIΔ54) still possesses moderate membrane affinity. We demonstrate that incorporation of nickel-NTA lipids in membranes enhances the membrane affinity and the membrane lytic activity of VIΔ54. We also demonstrate that 3 predicted pVI α-helices within residues 54-114 associate with membranes, sitting roughly parallel to the membrane surface. His-tagged VIΔ54 is capable of fragmenting membranes similar to pVI and the VI-Φ peptide. Interestingly, neither VI-Φ nor His-tagged VIΔ54 can induce tubule formation in giant lipid vesicles as observed for pVI. These data suggest cooperativity between the amphipathic α-helix and residues in VIΔ54 to induce positive membrane curvature and tubule formation. These results provide additional details regarding the mechanism of nonenveloped virus membrane penetration.