Compression Characteristics of Proteo-Lipid Bilayers Comprised of Photosystem I SMALPs

Polymer-bound nanodiscs, such as styrene maleic acid lipid particles (SMALPs), have emerged as a technique for isolating membrane proteins that retain an annulus of native lipids, in bilayer conformation, surrounding the encapsulated protein. The preservation of the native membrane environment in these so-called “native nanodiscs” has been reported to exhibit more native-like biophysical activity in vitro for various protein complexes, across a myriad of biophysical studies, typically conducted free in solution. Here, we combine the SMALP technique with the Langmuir–Blodgett trough, to produce thin films comprised of photosystem I (PSI) SMALPs. This approach presents the ability to reconstitute of the native membrane architecture of uniform PSI arrays as seen in nature. Here, we report the conditions required to partition PSI–SMALPs to the air–water interface and achieve controlled compression into thin films. These parameters concern the physical interaction of SMALP particles and may be transferrable to other protein and lipid only SMALP systems. Furthermore, PSI–SMALP thin films exhibit greater stability than those comprised of PSI detergent micelles and demonstrate a lower surface compression modulus compared to lipid only monolayers. Individual PSI–SMALPs retain their size following decompression from the thin film conformation, consistent with retention of the overall PSI–SMALP particle architecture. This platform offers a more accurate biomimetic system from which to probe fundamental questions and drive applied work.