A Density Functional Theory Study on Trimethylamine <i>N</i> ‐Oxide Interactions with Amino Acid Side Chain Models: Probing the Driving Force of Lysozyme Aggregation

Trimethylamine N-oxide (TMAO) is an osmolyte whose role in protein aggregation is poorly understood. We investigate the molecular basis of the phenomenon where TMAO increases the denaturation temperature of lysozyme while simultaneously inducing its irreversible aggregation. Using density functional theory (DFT), we analyzed the thermodynamics of TMAO's interaction with protein fragments exposed during denaturation. The results indicate that TMAO forms energetically favorable interactions with numerous fragments, particularly with the peptide backbone and the side chains of serine, threonine, tyrosine, and lysine, in contrast to acidic residues. This preferential binding stabilizes the denatured state, which facilitates interchain contacts and initiates aggregation. These findings provide a molecular explanation for the proaggregating role of TMAO toward denatured lysozyme.