Influence of molecular weight of PEG chain on interaction between streptavidin and biotin–PEG-conjugated phospholipids studied with QCM-D

Poly(ethylene glycol)-conjugated phospholipid (PEG-lipid) derivatives spontaneously incorporate into lipid bilayer membranes, thus, they are useful for immobilizing bioactive substances onto cell surfaces. Here, we investigated how the density and molecular weight of PEG molecules influenced immobilization and cellular uptake of a bioactive substance. We analyzed how three biotin–PEG-lipids (1k, 5k, and 40k, with PEG molecular weights: 1 kD, 5 kD, and 40 kD, respectively) interacted with streptavidin on a surface attached to a quartz crystal microbalance with dissipation (QCM-D). We found that the volume excluded by 1k PEG could not effectively prevent adsorption of bovine serum albumin (BSA). In contrast, 5k PEG chains could completely prevent protein adsorption. However, due to strong static repulsion, 40k PEG chains could not be packed at high density. Thus, BSA migrated between PEG chains, and adsorption was not effectively prevented. When streptavidin was added, it bound to multiple neighboring sites on 1k and 5k biotin–PEG-lipids, which reduced chain viscoelasticity. In contrast, streptavidins bound at a one-to-one stoichiometry with the 40k biotin–PEG-lipids, which increased chain viscoelasticity. However, differences in PEG viscoelasticity and PEG molecular weights did not influence cellular uptake of immobilized streptavidin. Therefore, these are not important factors in designing polymers that prevent cellular endocytosis.