Pressure, Peptides, and a Piezolyte: Structural Analysis of the Effects of Pressure and Trimethylamine-N-oxide on the Peptide Solvation Shell

Abstract

The osmolyte trimethylamine-N-oxide (TMAO) is able to increase the thermodynamic stability of folded proteins, counteracting pressure denaturation. Herein, we report experimental solubility data on penta-alanine (pAla) in aqueous TMAO solutions (at pH = 7 and pH = 13) together with molecular simulation data for pAla, penta-serine (pSer), and an elastin-like peptide (ELP) sequence (VPGVG) under varying pH and pressure conditions. The effect of the peptide end groups on TMAO− peptide interactions is investigated by comparing the solvation of zwitterionic and negatively charged pentamers with the solvation of pentamers with charge-neutral C-and N-termini and linear, virtually infinite, peptide chains stretched across the periodic boundaries of the simulation cell. The experiments and simulations consistently show that TMAO is net-depleted from the pAla−water interface, but local accumulation of TMAO is observed just outside the first hydration shell of the peptide. While the same observations are also made in the simulations of the zwitterionic pentamers (Ala, Ser, and ELP) and virtually infinite peptide chains (Ala and ELP), weak preferential binding of TMAO is instead observed for pAla with neutral end groups at a 1 M TMAO concentration and for an ELP pentamer with capped neutral end groups at a 0.55 M TMAO concentration studied in previous work (Y.-T. Liao et al. Proc. Natl. Acad. Sci. USA, 2017USA, , 114, 2479USA, −2484. The above observations made at 1 bar ambient pressure remain qualitatively unchanged at 500 bar and 2 kbar. Local accumulation of TMAO correlates with a reduction in the total number of peptide−solvent hydrogen bonds, independent of the peptide's primary sequence and the applied pressure. By weakening water hydrogen bonds with the protein backbone, TMAO indirectly contributes to stabilizing internal hydrogen bonds in proteins, thus providing a protein stabilization mechanism beyond net depletion.

Deep sea osmolytes in action: their effect on protein–ligand binding under high pressure stress

“…For TMAO, however, significant progress has been made in the last years to develop pressure dependent force-fields, which reproduce solution thermodynamics and have been successfully applied to explain thermodynamic stabilization of various peptide sequences. 33,58 Changes in protein dynamics can also be caused by the solvent. 59 Osmolytes can alter the ability of residues to move, rearrange and even lead to changes in the internal protein dynamics.…”

“…For TMAO, however, significant progress has been made in the last years to develop pressure dependent force-fields, which reproduce solution thermodynamics and have been successfully applied to explain thermodynamic stabilization of various peptide sequences. 33,58…”

“…[18][19][20][21][22][23][24] Some studies suggested that TMAO can be slightly attracted to nonpolar groups in proteins. [30][31][32][33]…”

Counterintuitive Electrostatics upon Metal Ion Coordination to a Receptor with Two Homotopic Binding Sites

“…In order to further investigate this observation, the distributions of the counterions around the BCETB surface were analyzed. Figure 9 shows local/bulk partition coefficients of the different counterions with respect to the BCETB surface defined as 39 Here, d is the distance from the BCETB surface, ⟨ n surf,ion ( d )⟩ and ⟨ n surf,water ( d )⟩ are the average numbers of counterions and water molecules, respectively, populating a region within [0, d ] from the BCETB surface, whereas N ion and N water are the total numbers of counterions and water molecules, respectively, in the simulation box. For thiocyanate, we calculated K p ( d ) for the individual atoms separately, to get insight into the relative affinities of the sulfur, nitrogen, and carbon atoms to BCETB.…”

TMAO: Protecting Proteins from Feeling the Heat

“…The maximum amount of TMAO that has been found in marine organisms is about 0.9 M (4), and solubility is sometimes cited as the cause (4, 5). However, TMAO is soluble at concentrations above 4 M in water at 20 °C, (20,45) and remains soluble above 1.5 M even at 12 kbar (1, 2). We propose instead that the protein stabilization plateau (Fig.…”