Lipid nanodiscs are widely used platforms for studying membrane proteins in a near-native environment. Lipid nanodiscs made with membrane scaffold proteins (MSPs) in the linear form have been well studied. Recently, a new kind of nanodisc made with MSPs in the circular form, referred to as covalently circularized nanodiscs (cNDs), has been reported to have some possible advantages in various applications. Given the potential of nanodisc technology, researchers in the field are very interested in learning more about this new kind of nanodisc, such as its reproducibility, production yield, and the possible pros and cons of using it. However, research on these issues is lacking. Here, we report a new study on nanodiscs made with circular MSPs, which are produced from a method different from the previously reported method. We show that our novel production method, detergent-assisted sortase-mediated ligation, can effectively avoid high-molecular-weight byproducts and also significantly improve the yield of the target proteins up to around 80% for larger circular MSP constructs. In terms of the application of circular MSPs, we demonstrate that they can be used to assemble nanodiscs using both synthetic lipids and native lipid extract as the source of lipids. We also show that bacteriorhodopsin can be successfully incorporated into this new kind of cND. Moreover, we found that cNDs have improved stability against both heat and high-concentration-induced aggregations, making them more beneficial for related applications.

Lipid–porphyrin conjugates are considered nowadays as promising building blocks for the conception of supramolecular structures with multifunctional properties, required for efficient cancer therapy by photodynamic therapy (PDT). The synthesis of two new lipid–porphyrin conjugates coupling pheophorbide‐a (Pheo‐a), a photosensitizer derived from chlorophyll‐a, to either chemically modified lyso‐phosphatidylcholine (PhLPC) or egg lyso‐sphingomyelin (PhLSM) is reported. The impact of the lipid backbone of these conjugates on their self‐assembling properties, as well as on their physicochemical properties, including interfacial behavior at the air/buffer interface, fluorescence and absorption properties, thermotropic behavior, and incorporation rate in the membrane of liposomes were studied. Finally, their photodynamic activity was evaluated on esophageal squamous cell carcinoma (ESCC) and normal esophageal squamous epithelium cell lines. The liposome‐like vesicles resulting from self‐assembly of the pure conjugates were unstable and turned into aggregates with undefined structure within few days. However, both lipid–porphyrin conjugates could be efficiently incorporated in lipid vesicles, with higher loading rates than unconjugated Pheo‐a. Interestingly, phototoxicity tests of free and liposome‐incorporated lipid–porphyrin conjugates demonstrated a better selectivity in vitro to esophageal squamous cell carcinoma relative to normal cells.