The formation of ordered cross-β amyloid protein aggregates is associated with a variety of human disorders. While conventional infrared methods serve as sensitive reporters of the presence of these amyloids, the recently discovered amyloid secondary structure of cross-α fibrils presents new questions and challenges. Herein, we report results using Fourier transform infrared spectroscopy and two-dimensional infrared spectroscopy to monitor the aggregation of one such cross-α–forming peptide, phenol soluble modulin alpha 3 (PSMα3). Phenol soluble modulins (PSMs) are involved in the formation and stabilization of Staphylococcus aureus biofilms, making sensitive methods of detecting and characterizing these fibrils a pressing need. Our experimental data coupled with spectroscopic simulations reveals the simultaneous presence of cross-α and cross-β polymorphs within samples of PSMα3 fibrils. We also report a new spectroscopic feature indicative of cross-α fibrils.
Wide-field imaging through dielectric microspheres has emerged in recent years as a simple and effective approach for generating super-resolution images at visible wavelengths. We present, to our knowledge, the first demonstration that dielectric microspheres can be used in a wide-field infrared (IR) microscope to enhance the far field resolution. We have observed a substantial improvement in resolution and magnification when images are collected through polystyrene microspheres. In addition, we demonstrate that spectroscopic imaging with a pulse-shaper based femtosecond mid-IR laser system is possible through the dielectric microspheres, which is a promising first step toward applying this technique to ultrafast IR imaging methods such as pump–probe and 2DIR microscopy.
Two-dimensional infrared spectroscopy reveals folding of an intrinsically disordered peptide when sequestered into a model “membrane-less” organelle.
<p>Proline-arginine (PR) dipeptide repeats have been shown to undergo liquid-liquid phase separation and are an example of a growing number of intrinsically disordered proteins that can assemble into membraneless organelles. These structures have been posited as a nucleation site for pathogenic protein aggregation. As such, a better understanding of the effects that the increased local concentration and volumetric crowding within droplets has on peptide secondary structure is necessary. Herein we use Fourier transform infrared (FTIR) and two-dimensional infrared (2DIR) spectroscopy to show that formation of droplets by PR20 accompany changes in the Amide-I spectra consistent with folding into poly-proline helical structures. </p>
The formation of ordered cross-β amyloid protein aggregates is associated with a variety of human disorders. While conventional infrared methods serve as sensitive reporters of the presence of these amyloids, the recently discovered amyloid secondary structure of cross- fibrils presents new questions and challenges. Herein, we report results using Fourier Transform infrared (FTIR) spectroscopy and two-dimensional infrared (2DIR) spectroscopy, to monitor the aggregation of one such cross-alpha forming peptide, phenol soluble modulin alpha 3 (PSM⍺3). Phenol soluble modulins (PSMs) are involved in the formation and stabilization of Staphylococcus aureus biofilms, making sensitive methods of detecting and characterizing these fibrils a pressing need. Our experimental data, coupled with spectroscopic simulations, reveals the simultaneous presence of cross-⍺ and cross-β polymorphs within samples of PSM⍺3 fibrils. We also report a new spectroscopic feature indicative of cross-alpha fibrils.
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