## 2 Materials and Methods
The molar ratio [Gb3]/[POPC] of the mixture was 0.1/1 with the concentration of POPC fixed at 1% _w/v_. The Cy3-StxB was mixed with BODIPY-GUVs in molar ratio of 1:2 and incubated at room temperature for 30 min. GUVs were examined under an inverted confocal fluorescence microscope (Leica SP8, Leica, Wetzlar, Germany) equipped with a Zeiss \(\times\) 63 PL APO HCX, 1.4 NA oil immersion objective. **SUV Sample Preparation. ** Small unilamellar vesicles (SUVs) used for SAXS and SANS measurement were prepared in reference with [PERSON] et al. with the following modifications [20]. Briefly, the Gb3 was selected as the glycosphingolipid candidate to constitute the SUVs. Both protiated (1,2-dipalmitoyl-sn-glycero-3-phosphocholine (h-DPPC), Avanti Polar Lipids (Alabaster, AL, USA)) and deuterated phosphorlipids (1,2-dipalmitoyl-d62-sn-glycero-3-phosphocholine (d-DPPC), Avanti Polar Lipids (Alabaster, AL, USA)) were used to build proper electron density contrast variations for neutron scattering, and the prepared sample solutions were extruded 21 times through 0.1\(\upmu\)m polycarbonate Nucleore(tm) membranes using Avanti Mini-Extruder (Avanti Polar Lipids, Alabaster, AL, USA) before the scattering measurements. **X-ray, Neutron, and Light Scattering Experiments. ** Small-angle X-ray scattering measurements were performed at beamline BL19U2 of National Facility for Protein Science Shanghai (NFPS) at Shanghai Synchrotron Radiation Facility (SSRF) in reference to our previous work [21]. The wavelength, \(\uplambda\), of X-ray radiation was set as 1.033 A. Scattered X-ray intensities were collected using a Pilatus 1 M detector (DECTRIS Ltd., Baden-Daettwil, Switzerland). The sample-to-detector distance was set such that the detecting range of momentum transfer [\(q=4\pi\sin\theta/\uplambda\), where 20 is the scattering angle] of SAXS experiments was 0.1-4.5 nm\({}^{-1}\). SAXS data were collected in cylindrical quartz capillary with a diameter of 1.5 mm and a wall of 10 \(\upmu\)m as 20 \(\times\) 1 s exposures and scattering profiles for the 20 passes were compared at 25 \({}^{\circ}\)C using 60 \(\upmu\)L sample. Small-angle neutron scattering measurement were carried out using the time of flight SANS spectrometer installed at V16 beam port at the research reactor BERII of Helmholtz-Zentrum in Berlin (HZB), Berlin, Germany [22]. In order to cover a wide q-range from 0.036 to 7.0 nm\({}^{-1}\), each sample was measured at two samples to detector distances 2 m and 11 m, respectively. The cell unit is made of quartz and the SANS measurement was taken at 25 \({}^{\circ}\)C with an exposure time of 200 min. The data were corrected for the transmission and scattering background, and the absolute scattering intensity was obtained by using water scattering as a standard reference. The SANS and SAXS measurements were performed at the same temperatures. Dynamic light scattering (DLS) measurements were carried out by using the dynamic light scattering detection device (Wyatt DynaPro NanoStar, Santa Barbara, CA, USA). The temperature of the samples was the same in the SANS and SAXS measurements. **Small-angle scattering Data Analysis. ** The scattering data were fitted by a bilayer vesicle model, written as  
\[I(q)=\left[ \begin{array}{c}K(q,R_{\rm c},\eta_{\rm sol}-\eta_{\rm t})+K(q,R_ {\rm c}+t_{\rm tr},\eta_{\rm t}-\eta_{\rm h})\\ +K(q,R_{\rm c}+t_{\rm t}+t_{\rm h},\eta_{\rm h}-\eta_{\rm t})+K(q,R_{\rm c}+2t_ {\rm t}+t_{\rm h},\eta_{\rm t}-\eta_{\rm sol})\end{array} \right]^{2} \tag{1}\]  
\[K(q,R,\triangle\eta)=4\pi R^{3}\triangle\eta\frac{\sin(qR)-qR\cos(qR)}{(qR)^{3}} \tag{2}\]  
where \(R_{\rm c}\) is the radius of the core, \(t_{\rm h}\) is the thickness of the outer part of bilayer (in contact with solvent), \(t_{\rm t}\) is the thickness of the inner part of bilayer, \(\eta_{\rm sol}\), \(\eta_{\rm h}\) and \(\eta_{\rm t}\) are the scattering length densities of solvent, outer part of bilayer, and inter part of bilayer, respectively.