Analysis of Lipid Phase Behavior and Protein ConformationalChanges in Nanolipoprotein Particles upon Entrapment in Sol–Gel-DerivedSilica

摘要

The entrapment of nanolipoprotein particles (NLPs) and liposomes in transparent, nanoporous silica gel derived from the precursor tetramethylorthosilicate was investigated. NLPs are discoidal patches of lipid bilayer that are belted by amphiphilic scaffold proteins and have an average thickness of 5 nm. The NLPs in this work had a diameter of roughly 15 nm and utilized membrane scaffold protein (MSP), a genetically altered variant of apolipoprotein A-I. Liposomes have previously been examined inside of silica sol–gels and have been shown to exhibit instability. This is attributed to their size (∼150 nm) and altered structure and constrained lipid dynamics upon entrapment within the nanometer-scale pores (5–50 nm) of the silica gel. By contrast, the dimensional match of NLPs with the intrinsic pore sizes of silica gel opens the possibility for their entrapment without disruption. Here we demonstrate that NLPs are more compatible with the nanometer-scale size of the porous environment by analysis of lipid phase behavior via fluorescence anisotropy and analysis of scaffold protein secondary structure viacircular dichroism spectroscopy. Our results showed that the lipidphase behavior of NLPs entrapped inside of silica gel display closerresemblance to its solution behavior, more so than liposomes, andthat the MSP in the NLPs maintain the high degree of α-helixsecondary structure associated with functional protein–lipidinteractions after entrapment. We also examined the effects of residualmethanol on lipid phase behavior and the size of NLPs and found thatit exerts different influences in solution and in silica gel; unlikein free solution, silica entrapment may be inhibiting NLP size increaseand/or aggregation. These findings set precedence for a bioinorganichybrid nanomaterial that could incorporate functional integral membraneproteins.