Fig. 1: Membrane deformation after polyvalent lipid binding is a common mechanism of viral endocytosis.

A Spinning disc confocal fluorescence microscopy micrographs of polyomavirus-like particles (VLPs) bound to Giant unilamellar vesicles (GUVs) containing receptor gangliosides. 2 µg of each VLP was incubated for 1 h at RT with GUVs containing the indicated gangliosides (98% DOPC, 1% ganglioside, 1% β-BODIPY FL C12-HPC dye) and imaged at the equatorial plane. Scale bar is 2 µm. B Spinning disc confocal fluorescence microscopy micrographs of polyoma VLPs bound to energy-depleted CV1 cells. Cells were starved of cellular energy by 30 min incubation in starvation buffer (PBS +/+ supplemented with 10 mM 2-deoxy-D-glucose and 10 mM NaN3) followed by 1 h incubation with 5 µg of each VLP in starvation buffer and imaged live on a spinning disk confocal microscope. DiI membrane dye was added 10 min prior to imaging at 1 mg/ml final concentration. Scale bars are 5 µm and 1 µm for insets. Arrows mark VLP-filled membrane invaginations. C Quantification of colocalization in confocal fluorescence micrographs between polyomavirus VLPs and lysosomes as marked by Lamp1-GFP in live cells. CV1 cells expressing Lamp1-EGFP were kept at 4 °C for 10 min before incubation with 2 µg of the indicated VLPs for 30 min at 4 °C, followed by further incubation at 37 °C for the indicated times before imaging live on a spinning disk confocal microscope. Means ± s.e.m. from n = 3 independent experiments. D Representative confocal fluorescence micrographs of the Lamp1-EGFP expressing cells containing the indicated VLPs after 6 h incubation at 37 °C. Scale bars are 5 µm and 1 µm for insets. Magenta: VLPs, Cyan: membrane marker or Lamp1-EGFP. Source data are provided as a Source Data file.