Characteristic Raman Optical Activity Signatures of Protein β-Sheets

Measurement and Theory of Resonance Raman Optical Activity for Gases, Liquids, and Aggregates. What It Tells about Molecules

Resonance Raman Optical Activity (RROA) appeared as a natural extension of the nonresonance branch. It combines the structural sensitivity of chiroptical spectroscopy with the signal enhancement coming from the resonance of molecular electronic transitions with the excitation laser light. However, the idea has been hampered by many technical and theoretical problems that are being clarified only in recent years. We provide the theoretical basis and several examples documenting the problems, achievements, and potential of RROA, in particular in biomolecular studies.

Indication of Neurodegenerative Cascade Initiation by Amyloid-like Aggregate-Forming EBV Proteins and Peptide in Alzheimer's Disease

The neurotropic potential of the Epstein-Barr virus (EBV) was demonstrated quite recently; however, the mechanistic details are yet to be explored. Therefore, the effects of EBV infection in the neural milieu remain underexplored. Previous reports have suggested the potential role of virus-derived peptides in seeding the amyloid-β aggregation cascade, which lies at the center of Alzheimer's disease (AD) pathophysiology. However, no such study has been undertaken to explore the role of EBV peptides in AD. In our research, ∼100 EBV proteins were analyzed for their aggregation proclivity in silico using bioinformatic tools, followed by the prediction of 20S proteasomal cleavage sites using online algorithms NetChop ver. 3.1 and Pcleavage, thereby mimicking the cellular proteasomal cleavage activity generating short antigenic peptides of viral origin. Our study reports a high aggregate-forming tendency of a 12-amino-acid-long (₁₄₆SYKHVFLSAFVY₁₅₇) peptide derived from EBV glycoprotein M (EBV-gM). The in vitro analysis of aggregate formation done using Congo red and Thioflavin-S assays demonstrated dose- and time-dependent kinetics. Thereafter, Raman spectroscopy was used to validate the formation of secondary structures (α helix, β sheets) in the aggregates. Additionally, cytotoxicity assay revealed that even a low concentration of these aggregates has a lethal effect on neuroblastoma cells. The findings of this study provide insights into the mechanistic role of EBV in AD and open up new avenues to explore in the future.

Paving the way to conformationally unravel complex glycopeptide antibiotics by means of Raman optical activity

It is crucial for fundamental physical chemistry techniques to find their application in tackling real-world challenges. Hitherto, Raman optical activity (ROA) spectroscopy is one of the examples where a promising future within the pharmaceutical sector is foreseen, but has not yet been established. Namely, the technique is believed to be able to contribute in investigating the conformational behaviour of drug candidates. We, herein, strive towards the alignment of the ROA analysis outcome and the pharmaceutical expectations by proposing a fresh strategy that ensures a more complete, reliable, and transferable ROA study. The strategy consists of the treatment of the conformational space by means of a principal component analysis (PCA) and a clustering algorithm, succeeded by a thorough ROA spectral analysis and a novel way of estimating the contributions of the different chemical fragments to the total ROA spectral intensities. Here, vancomycin, an antibiotic glycopeptide, has been treated; it is the first antibiotic glycopeptide studied by means of ROA and is a challenging compound in ROA terms. By applying our approach we discover that ROA is capable of independently identifying the correct conformation of vancomycin in aqueous solution. In addition, we have a clear idea of what ROA can and cannot tell us regarding glycopeptides. Finally, the glycopeptide class turns out to be a spectroscopically curious case, as its spectral responses are unlike the typical ROA spectral responses of peptides and carbohydrates. This preludes future ROA studies of this intriguing molecular class.

The effect of protein backbone hydration on the amide vibrations in Raman and Raman optical activity spectra

Raman and specifically Raman optical activity (ROA) spectroscopy are very sensitive to the solution structure and conformation of biomolecules. Because of this strong conformational sensitivity, density functional theory (DFT) calculations are often used to get a better understanding of the experimentally observed spectral patterns. While e.g. for carbohydrate structure the water molecules that surround the solute have been demonstrated to be of vital importance to get accurate modelled ROA spectra, the effect of explicit water molecules on the calculated ROA patterns of peptides and proteins is less well studied. Here, the effect of protein backbone hydration was studied using DFT calculations of HCO-(l-Ala)5-NH2 in specific secondary structure conformations with different treatments of the solvation. The effect of the explicit water molecules on the calculated spectra mainly arises from the formation of hydrogen bonds with the amide C[double bond, length as m-dash]O and N-H groups. Hydrogen bonding of water with the C[double bond, length as m-dash]O group determines the shape and position of the amide I band. The C[double bond, length as m-dash]O bond length increases upon formation of C[double bond, length as m-dash]OH2O hydrogen bonds. The effect of the explicit water molecules on the amide III vibrations arises from hydrogen bonding of the solvent with both the C[double bond, length as m-dash]O and N-H group, but their contributions to this spectral region differ: geometrically, the formation of a C[double bond, length as m-dash]OH2O bond decreases the C-N bond length, while upon forming a N-HH2O hydrogen bond, the N-H bond length increases.

Tracking Conformational Changes in Phosvitin throughout a Crowding-Agent-Based Titration

The sensitivity of Raman optical activity (ROA) towards small conformational changes is explored by tracking the structural changes in an intrinsically disordered protein-phosvitin-induced by different concentrations of crowding agent. It is shown that ROA is capable of tracking small conformational changes involving β-sheet and α-helical secondary structural properties of the protein. Furthermore, it is indicated that the influences of the crowding agents employed, Ficoll 70 and dextran 70, on the structural properties of phosvitin differ significantly, with the structural changes induced by the presence of Ficoll 70 being more pronounced and already being visible at a lower concentration. The data also suggest that some spectral changes do not arise from a change in the secondary structure of the protein, but are related to differences in interaction between the phosphorylated residues of the protein and the sugar-based crowding agent.

Conformational Disorder and Dynamics of Proteins Sensed by Raman Optical Activity

Raman optical activity (ROA) spectra of proteins hold a lot of information about their structure in solution. To create a better understanding of the ROA spectra of, among others, the intrinsically disordered proteins (IDPs), involved in neurodegenerative diseases, the effect of conformational disorder and dynamics on the ROA spectra was studied. Density functional theory (DFT) calculations of small ensembles of model peptides with increasing disorder show that the ROA patterns of α-helical and polyproline II (PPII) structure reflect the average backbone angles in the ensemble. The amide III region in the ROA spectra of the α-helical peptides is shown to retain its typical -/+/+ pattern, while the amide III region of PPII secondary structure diminishes in intensity with increasing structural disorder. The results show that the ROA spectra of IDPs hence more likely stem from short stretches of well-defined PPII helices rather than a very flexible chain. Further DFT calculations support that mixing of PPII with helical secondary structure is consistent with experimental spectra of IDPs, while mixing with β-strand results in spectral patterns that are not observed experimentally. The detailed information obtained from these results contributes to a better understanding of the spectrum-structure relation.

Establishing the link between fibril formation and Raman optical activity spectra of insulin

Molecular dynamics and density functional simulations are used to explain changes in Raman optical activity accompanying the formation of insulin fibrils.

Multiscale simulations for understanding the evolution and mechanism of hierarchical peptide self-assembly

Multiscale molecular simulations that combine and systematically link several hierarchies can provide insights into the evolution and dynamics of hierarchical peptide self-assembly from the molecular level to the mesoscale.

The potential of chiroptical and vibrational spectroscopy of blood plasma for the discrimination between colon cancer patients and the control group

Colorectal cancer is one of the most abundant causes of cancer deaths in the world. At an early stage, the established clinical procedures have low reliability and sensitivity. Therefore, we tested a novel approach based on chiroptical methods such as electronic circular dichroism (ECD) and Raman optical activity (ROA). These methods are suitable for detecting slight changes in the 3D structure of chiral biomolecules, some of which may be caused by pathological processes occurring during cancer growth. Fifty-five blood plasma samples were analyzed using the combination of ECD and ROA supplemented by conventional Raman and FT-IR spectroscopy. All obtained spectra were evaluated together by linear discriminant analysis. The accuracy of sample discrimination reached 100% and the subsequent leave-one-out cross-validation resulted in 93% sensitivity and 81% specificity. The achieved results indicate that chiroptical methods supplemented by Raman and FT-IR spectroscopy might be new supporting and minimally invasive tools in the clinical diagnosis of colon cancer.