Unraveling How Multivalency Triggers Shape Deformation of Sub-100 nm Lipid Vesicles

Abstract

Multivalent ligand−receptor interactions are critical to the function of membrane-enveloped biological and biomimetic nanoparticles, yet resulting nanoparticle shape changes are rarely investigated. Using the localized surface plasmon resonance (LSPR) sensing technique, we tracked the attachment of biotinylated, sub-100 nm lipid vesicles to a streptavidin-functionalized supported lipid bilayer (SLB) and developed an analytical model to extract quantitative details about the vesicle−SLB contact region. The experimental results were supported by theoretical analyses of biotin−streptavidin complex formation and corresponding structural and energetic aspects of vesicle deformation. Our findings reveal how varying the surface densities of streptavidin receptors in the SLB and biotin ligands in the vesicles affects the extent of nanometer-scale vesicle deformation. We also identify conditions, i.e., a critical ligand density, at which appreciable vesicle deformation began, which provides insight into how the membrane bending energy partially counterposes the multivalent binding interaction energy. These findings are generalizable to various multivalent ligand−receptor systems.

Dissimilar Deformation of Fluid- and Gel-Phase Liposomes upon Multivalent Interaction with Cell Membrane Mimics Revealed Using Dual-Wavelength Surface Plasmon Resonance

“…The first general conclusion from these data is that the deformation of liposomes is modest in all cases. Another conclusion is that the biotin concentration in the SLB seemingly plays a nearly negligible role for the deformation of the 70 nm liposomes, 14 whereas its role in our study of the 105 nm liposomes is somewhat more appreciable. This difference may be related to the liposome coverage.…”

“…It is of interest that, despite a similar scale of deformation of gel-phase liposomes, the earlier conclusions concerning this factor are different and imply membrane bending 14 with a high value of k b (∼700k B T) and high adhesion-induced osmotic pressure (∼0.5 MPa) in combination with k b = 10−30k B T (Figure 4a in ref 18; note that the liposomes used in that work are not biotinylated). In our case, the number of biotin−streptavidin complexes is ∼56−184, the binding energy per complex is ∼12 kcal/mol, 14 i.e., around 20k B T, and, accordingly, the total binding energy is on the order of 2 × 10 3 k B T. The osmotic pressure is determined primarily by NaCl, and its scale is P os = 2Δck B T, where Δc = 150 − 137 = 13 mM is the difference of the NaCl concentrations during the preparation of and experiments with liposomes. The deformation of liposomes is modest, and the corresponding scale of the change of the osmotic pressure related energy can be estimated as…”

“…where S λ is the sensitivity factor and (dn/dc) λ is the derivative of the refractive index with respect to the molecular concentration. In our case, the attached vesicles can be represented by a sphere in the undeformed state or by a truncated sphere with a flat basement (Figure 2) in the deformed state (this model was earlier used in the SPR context 19 and also in the LSPR context 14 ), and we have (see eq S1 in ref 19 and note that we have corrected a misprint there)…”

“…These methods are, however, typically applied to giant unilamellar vesicles and bilayer stacks and are not suitable to quantify ∼100 nm diameter liposomes. This difference in sizes is important, because there are indications that the bending rigidity, k b , appreciably increases with decreasing diameter down to ∼100 nm . More recently, atomic force microscopy (AFM) has become popular for characterizing surface-bound nanoscale liposomes through their controlled deformation using tip induced indentation. − In particular, the attachment of ∼100 nm diameter biotin-modified liposomes to a streptavidin-modified supported lipid bilayer (SLB) was scrutinized .…”

Distinct Binding Properties of Neutravidin and Streptavidin Proteins to Biotinylated Supported Lipid Bilayers: Implications for Sensor Functionalization

“…It is also possible to analyze time-independent plots of the two signals, which can lead to insights into adsorbate configuration and conformational changes from a comparative perspective [40]. Since the QCM-D technique is label-free, there is no requirement for protein labeling and comparable measurement response trends for protein attachment have also been obtained with other biosensing techniques such as localized surface plasmon resonance (LSPR) [41], thus establishing the QCM-D as a useful tool for biomacromolecular characterization in the present study. As mentioned above, we first fabricated a biotinylated SLB on the sensor chip surface in Tris buffer (pH 7.5), which resulted in final ∆f and ∆D shifts of around −25 ± 3 Hz and less than 1 × 10 −6 , respectively.…”