Modeling amide-I vibrations of alanine dipeptide in solution by using neural network protocol

Dissecting amide-I vibrations in histidine dipeptide

The amide-I vibrational characteristics and conformational preferences of the model compound - histidine dipeptide (Ac-His-NHCH₃, HISD) in gas phase and solution have been revealed with the help of ab initio calculations and wavefunction analyses. The Gibbs free energy surfaces (FESs) of solvated HISD were smoothed by solvent effect to exhibit different structural populations concerning various external environments. It was shown that the most stable conformations of HISD in CHCl₃ and gas phase are C7eq, while those in DMSO and water are β and PPII, respectively. Compared with ALAD, the number of accessible conformational states on these FESs was predicted to be reduced due to the steric effect of imidazole group. The two amide-I normal modes of HISD were found to have intrinsically secondary structural dependencies, and be sensitive to surrounding environments. The average amide-I_a frequencies of HISD isomers in these environments were predicted to be almost the same as those of ALAD, while the amide-I_b mean frequencies were estimated to be lower than ALAD due to the intramolecular interactions between the imidazole group and amino-terminal amide unit. The good linear correlations between amide-I frequencies and the atomic electrostatic potentials (ESPs) of amide groups were also found to interpret the solvent-induced amide-I frequency shifts of HISD at the electronic structure level. These results allow us to gain a deep understanding of amide-I vibrations of HISD, and would be helpful for the site-specific conformational monitoring and spectral interpretation of solvated polypeptides.

Controllable membrane damage by tunable peptide aggregation with albumin

Aggregation of otherwise soluble proteins into amyloid structures is a hallmark of many disorders, such as Alzheimer's and Parkinson's disease. There is an increasing evidence that the small aggregations, instead of ordered fibrillar aggregates, are the main structures causing toxicity. However, the studies on the small aggregation phase are limited due to the variety of structures and the complexity of the physiological environment. Here, we showed an engineered co-assembling oppositely charged amyloid-like peptide pair ([II]) as a simple tool to establish methodologies to study the mechanism and kinetics of aggregation and relate its aggregation to toxicity. The toxicity mechanism of [II] is through cell membrane damage and stress, shown with YAP and eIF2α, as in the amyloid protein-initiated diseases. Albumin is demonstrated as an extrinsic and physiologically relevant molecule in controlling the aggregation lag time and toxicity of [II]. This study represents a molecular engineering strategy to create simplistic molecular tools for establishing methodologies to study the aggregation process and kinetics of amyloid-like proteins in various conditions. Understanding the nature of protein aggregation kinetics and linking them to their biological functions through engineered peptides paves the way for future designs and drug development applications.