Abstract
Optical spectroscopic methods do not routinely provide information on higher order hierarchical structure (tertiary/quaternary) of biological macromolecules and assemblies. This necessitates the use of time-consuming and material intensive techniques, such as protein crystallography, NMR, and electron microscopy. Here we demonstrate a spectroscopic phenomenon, superchiral polarimetry, which can rapidly characterize ligand-induced changes in protein higher order (tertiary/quaternary) structure at the picogram level, which is undetectable using conventional CD spectroscopy. This is achieved by utilizing the enhanced sensitivity of superchiral evanescent fields to mesoscale chiral structure.
Highlights
Protein crystallography, NMR, and microscopy are still routinely used to elucidate higher order biological structure
Metamaterials are composed of nanostructures with dimensions comparable to the wavelength of light enabling them to manipulate electromagnetic (EM) fields in unique ways, affording new opportunities in optics, spectroscopic detection, and characterization of matter.[1−5] In the present study we use a new label-free paradigm in chirally sensitive spectroscopy that allows changes in the chirality of tertiary and quaternary structure of a protein to be detected at picogram sensitivity
These fields are more sensitive to higher order structure than circularly polarized light (CPL) because there is a smaller mismatch between the effective helical pitch of a chiral evanescent field and the length scale of chirality of higher order structures, which is typically 10−100 nm
Summary
Communication states (Figure 2) for either the individual proteins or for proteins from related species.[20−25] The crystal structures reveal. Superchiral polarimetry is sensitive to the ligand-induced conformation change in EPSPS, which is undetectable to conventional CD spectroscopy For our studies, both the EPSPS and SK used were recombinant histidine tagged (His-tagged) proteins that were immobilized on the TPS surface using an established methodology (SI).[26] We estimate that the protein quantity adsorbed on the measured surface will be
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