Noncovalent Interactions between Trimethylamine N-Oxide (TMAO), Urea, and Water

Abstract

Trimethylamine N-oxide (TMAO) and urea are two important osmolytes with their main significance to the biophysical field being in how they uniquely interact with proteins. Urea is a strong protein destabilizing agent, whereas TMAO is known to counteract urea's deleterious effects. The exact mechanisms by which TMAO stabilizes and urea destabilizes folded proteins continue to be debated in the literature. Although recent evidence has suggested that urea binds directly to amino acid side chains to make protein folding less thermodynamically favored, it has also been suggested that urea acts indirectly to denature proteins by destabilizing the surrounding hydrogen bonding water networks. Here, we elucidate the molecular level mechanism of TMAO's unique ability to counteract urea's destabilizing nature by comparing Raman spectroscopic frequency shifts to the results of electronic structure calculations of microsolvated molecular clusters. Experimental and computational data suggest that the addition of TMAO into an aqueous solution of urea induces blue shifts in urea's H-N-H symmetric bending modes, which is evidence for direct interactions between the two cosolvents.

The Microbial Metabolite Trimethylamine N-Oxide Links Vascular Dysfunctions and the Autoimmune Disease Rheumatoid Arthritis

“…TMAO has beneficial as well as harmful effects. On the protective side, it serves as an osmolyte [6,36] that stabilizes protein structures against destabilizing forces, such as urea, and maintains the volume of intestinal cells under osmotic and hydrostatic stresses [34,37,54]. It supports oxidative phosphorylation as an electron acceptor for the Enterobacteriaceae flora that grows in the anaerobic intestine, thereby maintaining a healthy symbiotic balance in the microenvironment [29].…”

“…TMAO may critically benefit renal function in systemic inflammatory diseases by being a “chemical chaperone” to enhance the folding and stability of proteins, and an osmolyte to maintain cellular fluid balance [6,36]. It accumulates in the endoplasmic reticulum to promote protein folding, thereby inhibiting ER stress and attenuating the formation of intracellular aggregates [141].…”

“…For example, TMAO promotes inflammation in adipose tissue of mice on a high-fat and high-sugar diet [2]. Excessively high levels of TMAO is an established risk factor for CVD [3,4,5,6], glucose intolerance [2], kidney damage [7,8,9], obesity, and diabetes [10,11,12]. High levels may also increase the risk of colorectal, hepatic, and prostate cancer in humans [13].…”

Raman spectroscopic and quantum chemical investigation of the effects of trimethylamine N‐oxide on hydrated guanidinium and hydrogen‐bonded water networks

“…Full geometry optimizations and corresponding harmonic frequency calculations were performed on TMAO, guanidinium cation, and water using common DFT methods, specifically the M06‐2X [ 69 ] and ωB97XD functionals, [ 70 ] and using Dunning's aug‐cc‐pVDZ and aug‐cc‐pVTZ basis sets. [ 71–73 ] DFT methods have been previously used to study similar biomolecules, [ 28,39,68,74–78 ] with M06‐2X specifically being shown to account for the dispersion that affects the hydrogen bonding interactions occurring in aqueous solvation shells. [ 79–82 ] Lorentzian‐type functions for each normal mode were combined in order to create simulated Raman spectra.…”

“…[ 60,64–67 ] More recently, we showed that TMAO preferentially interacts with urea, which induces a blue shift (shift to higher energy) in the wavenumbers of the H‐N‐H symmetric bending mode of urea. [ 15,68 ]…”