Lipid Bilayer Coated Gold Nanoparticles Provide Insight Into Proteins' Conformational Changes

Abstract

While nanoparticles have been studied and used for many years and their unique chemical and physical properties have been extensively characterized, nanoparticles are now increasingly used to investigate biological systems. Nanoparticles can be formed on a submicron scale and do not interfere with normal biological processes, thus can be used in an in vivo system, allowing researchers to gain insight into its inner workings. The use of nanoparticles has also proven to be quite flexible, and has provided an indispensable tool in the advancement of drug delivery, tissue engineering, and detection of biomolecules. We have previously studied conformational changes occuring within proteins upon binding to phospholipid model membranes, particularly the tumor suppressor protein PTEN. To gain a more in depth characterization of these protein conformation changes, we have developed a technique in which we have fabricated 50nm gold nanoparticles coated with an asymmetric lipid bilayer, in a manner that allows us to control the identity of the lipids making up the outer leaflet. Using Raman spectroscopy, we will take advantage of the surface enhanced Raman spectroscopy (SERS) effect, which will increase PTEN band intensities binding of the protein to the lipid covered nanoparticle. Systematic mutation of tryptophan residues within the protein will allow us to probe the binding induced conformational changes in the vicinity of the tryptophan. While SERS has been used previously to study protein conformational changes, proteins were in these cases directly immobilized onto the nanoparticles. In contrast, our novel approach immobilizes the lipids on the nanoparticles and the protein can freely interact with the target lipid. While we plan to use these methods to examine PTEN, further development of this technique will allow for better study of conformational changes in a myriad of interfacial enzymes.