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1.
Proc Natl Acad Sci U S A ; 119(5)2022 02 01.
Artículo en Inglés | MEDLINE | ID: mdl-35078934

RESUMEN

The formation of ordered cross-ß 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-ß polymorphs within samples of PSMα3 fibrils. We also report a new spectroscopic feature indicative of cross-α fibrils.


Asunto(s)
Amiloide/genética , Toxinas Bacterianas/genética , Polimorfismo Genético/genética , Espectrofotometría Infrarroja/métodos , Espectroscopía Infrarroja por Transformada de Fourier/métodos , Staphylococcus aureus/genética
2.
J Chem Phys ; 156(3): 035102, 2022 Jan 21.
Artículo en Inglés | MEDLINE | ID: mdl-35065556

RESUMEN

The coupled amide-I vibrational modes in peptide systems such as fibrillar aggregates can often provide a wealth of structural information, although the associated spectra can be difficult to interpret. Using exciton scattering calculations, we characterized the polarization selective 2DIR peak patterns for cross-α peptide fibrils, a challenging system given the similarity between the monomeric and fibrillar structures, and interpret the results in light of recently collected 2D data on the cross-α peptide phenol soluble modulin α3. We find that stacking of α-helices into fibrils couples the bright modes across helical subunits, generating three new Bloch-like extended excitonic states that we designate A⊥, E∥, and E⊥. Coherent superpositions of these states in broadband 2DIR simulations lead to characteristic signals that are sensitive to fibril length and match the experimental 2DIR spectra.


Asunto(s)
Amidas , Péptidos , Modelos Químicos , Conformación Proteica en Hélice alfa , Espectrofotometría Infrarroja , Vibración
3.
J Phys Chem A ; 124(27): 5534-5541, 2020 Jul 09.
Artículo en Inglés | MEDLINE | ID: mdl-32543850

RESUMEN

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.

4.
Chem Sci ; 12(7): 2474-2479, 2020 Dec 29.
Artículo en Inglés | MEDLINE | ID: mdl-34164013

RESUMEN

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 nucleation sites for pathogenic protein aggregation. As such, a better understanding of the effects that the increased local concentration and volumetric crowding within droplets have 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 accompanies changes in the amide-I spectra consistent with folding into poly-proline helical structures.

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