Harnessing Liquid Crystal Sensors for High-Throughput Real-Time Detection of Structural Changes in Lysozyme during Refolding Processes

Abstract

Despite the rapid advances in process analytical technology, the assessment of protein refolding efficiency has largely relied on off-line protein-specific assays and/or chromatographic procedures such as reversed-phase high-performance liquid chromatography and size exclusion chromatography. Due to the inherent time gap pertaining to traditional methods, exploring optimum refolding conditions for many recombinant proteins, often expressed as insoluble inclusion bodies, has proven challenging. The present study describes a novel protein refolding sensor that utilizes liquid crystals (LCs) to discriminate varying protein structures during unfolding and refolding. An LC layer containing 4-cyano-4′-pentylbiphenyl (5CB) intercalated with 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) is used as a sensing platform, and its proof-of-concept performance is demonstrated using lysozyme as a model protein. As proteins unfold or refold, a local charge fluctuation at their surfaces modulates their interaction with zwitterionic phospholipid DOPE. This alters the alignment of DOPE molecules at the aqueous/LC interface, affecting the orientational ordering of bulk LC (i.e., homeotropic to planar for refolding and planar to homeotropic for unfolding). Differential polarized optical microscope images of the LC layer are subsequently generated, whose brightness directly linked to conformational changes of lysozyme molecules is quantified by gray scale analysis. Importantly, our LC-based refolding sensor is compatible with diverse refolding milieus for real-time analysis of lysozyme refolding and thus likely to facilitate the refolding studies of many proteins, especially those lacking a method to determine structure-dependent biological activity.