Oxidative stress may cause extended tyrosine posttranslational modifications of peptides and proteins. The 3-nitro-L-tyrosine (Nit), which is typically formed, affects protein behavior during neurodegenerative processes, such as Alzheimer's and Parkinson's diseases. Such metabolic products may be conveniently detected at very low concentrations by surface enhanced Raman spectroscopy (SERS). Previously, we have explored the SERS detection of the Nit NO2 bending vibrational bands in a presence of hydrogen chloride (Niederhafner et al., Amino Acids 53:517-532, 2021, ibid). In this article, we describe performance of a new SERS substrate, "pink silver", synthesized photochemically. It provides SERS even without the HCl induction, and the acid further decreases the detection limit about 9 times. Strong SERS bands were observed in the asymmetric (1550-1475 cm-1) and symmetric (1360-1290 cm-1) NO stretching in the NO2 group. The bending vibration was relatively weak, but appeared stronger when HCl was added. The band assignments were supported by density functional theory modeling.

• Klíčová slova
• Nitration, Oxidative stress, Photochemical synthesis, Posttranslational protein modification (PTM), Silver colloids, Surface enhanced Raman spectroscopy (SERS),
• MeSH
• oxid dusičitý MeSH
• peptidy MeSH
• proteiny MeSH
• Ramanova spektroskopie * metody   MeSH
• stříbro * chemie   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• oxid dusičitý MeSH
• peptidy MeSH
• proteiny MeSH
• stříbro * MeSH

Oxidative stress can lead to various derivatives of the tyrosine residue in peptides and proteins. A typical product is 3-nitro-L-tyrosine residue (Nit), which can affect protein behavior during neurodegenerative processes, such as those associated with Alzheimer's and Parkinson's diseases. Surface enhanced Raman spectroscopy (SERS) is a technique with potential for detecting peptides and their metabolic products at very low concentrations. To explore the applicability to Nit, we use SERS to monitor tyrosine nitration in Met-Enkephalin, rev-Prion protein, and α-synuclein models. Useful nitration indicators were the intensity ratio of two tyrosine marker bands at 825 and 870 cm-1 and a bending vibration of the nitro group. During the SERS measurement, a conversion of nitrotyrosine to azobenzene containing peptides was observed. The interpretation of the spectra has been based on density functional theory (DFT) simulations. The CAM-B3LYP and ωB97XD functionals were found to be most suitable for modeling the measured data. The secondary structure of the α-synuclein models was monitored by electronic and vibrational circular dichroism (ECD and VCD) spectroscopies and modeled by molecular dynamics (MD) simulations. The results suggest that the nitration in these peptides has a limited effect on the secondary structure, but may trigger their aggregation.

• Klíčová slova
• Density functional theory (DFT), Electronic circular dichroism (ECD), Nitration, Oxidative stress, Surface-enhanced Raman spectroscopy (SERS), Vibrational circular dichroism (VCD),
• MeSH
• azosloučeniny chemie   MeSH
• cirkulární dichroismus MeSH
• peptidy chemická syntéza   chemie   MeSH
• Ramanova spektroskopie metody   MeSH
• sekundární struktura proteinů MeSH
• simulace molekulární dynamiky MeSH
• teorie funkcionálu hustoty MeSH
• tyrosin analogy a deriváty   analýza   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• 3-nitrotyrosine MeSH Prohlížeč
• azobenzene MeSH Prohlížeč
• azosloučeniny MeSH
• peptidy MeSH
• tyrosin MeSH