Ion-specific binding of cations to the carboxylate and of anions to the amide of alanylalanine

Abstract

Studies of ion-specific effects on oligopeptides have aided our understanding of Hofmeister effects on proteins, yet the use of different model peptides and different experimental sensitivities have led to conflicting conclusions. To resolve these controversies, we study a small model peptide, L-Alanyl-L-alanine (2Ala), carrying all fundamental chemical protein motifs: C-terminus, amide bond, and N-terminus. We elucidate the effect of GdmCl, LiCl, KCl, KI, and KSCN by combining dielectric relaxation, nuclear magnetic resonance (1H-NMR), and (two-dimensional) infrared spectroscopy. Our dielectric results show that all ions reduce the rotational mobility of 2Ala, yet the magnitude of the reduction is larger for denaturing cations than for anions. The NMR chemical shifts of the amide group are particularly sensitive to denaturing anions, indicative of anion-amide interactions. Infrared experiments reveal that LiCl alters the spectral homogeneity and dynamics of the carboxylate, but not the amide group. Interaction of LiCl with the negatively charged pole of 2Ala, the COO− group, can explain the marked cationic effect on dipolar rotation, while interaction of anions between the poles, at the amide, only weakly perturbs dipolar dynamics. As such, our results provide a unifying view on ions’ preferential interaction sites at 2Ala and help rationalize Hofmeister effects on proteins.

Liquid–Liquid Phase Separation of the Intrinsically Disordered Domain of the Fused in Sarcoma Protein Results in Substantial Slowing of Hydration Dynamics

“…From such fits, we find very similar vibrational lifetimes (τ VER ) of 0.54 ± 0.03 ps for FUS LC 12E, 0.55 ± 0.03 ps for FUS LC BCs, and 0.48 ± 0.02 ps for FUS LC pH 11, which are close to the relaxation of the amide group of the dipeptide alanyl-alanine in D 2 O (0.7 ps). 45 In general, the value of τ VER is in line with what has been found for other proteins (∼1 ps 46,47 or less 31,37 ) and for the isolated amide moiety of N-methylacetamide (0.5 ps). 48 As such, in line with energy transfer from excited amide groups to the manifold of thermally accessible states being rather insensitive to the primary structure of proteins, we find that condensation also does not alter these dynamics.…”

“…To quantify this relaxation, we fit a single-exponential decay [ A 0 exp­(− T w /τ VER ) + y 0 ] to the integrated peak volumes (see Supplementary Figure 8). From such fits, we find very similar vibrational lifetimes (τ VER ) of 0.54 ± 0.03 ps for FUS LC 12E, 0.55 ± 0.03 ps for FUS LC BCs, and 0.48 ± 0.02 ps for FUS LC pH 11, which are close to the relaxation of the amide group of the dipeptide alanyl-alanine in D 2 O (0.7 ps) . In general, the value of τ VER is in line with what has been found for other proteins (∼1 ps , or less , ) and for the isolated amide moiety of N -methylacetamide (0.5 ps) .…”

“…A commercial 2D Quick IR (Phasetech Inc.) setup was used to record the 2D spectra of FUS LC. The exact setup is described elsewhere . Briefly, 800 nm laser pulses (7 W, 35 fs, 1 kHz) from a regenerative amplifier laser (Coherent, Astrella) were used to pump an optical parametric amplifier Topas Prime (Coherent) with a noncollinear difference frequency generation (NDFG) stage to generate pulses at 6000 nm (18 μJ, 400 cm –1 full width at half-maximum).…”

NMR analysis of the homodimeric structure of a D-Ala-D-Ala metallopeptidase, VanX, from vancomycin-resistant bacteria

“…The spectra represent measurements taken at 0, 34, and 470 min after the start of the reaction, catalyzed by VanX C78/157S, W24R . The two methyl groups were assigned based on a report 27 . (b) The molar ratios of the product, D-Ala, were calculated from the peak intensities (integrals) of the 1 H 1D spectra of VanX C78/157S and VanX C78/157S, W24R and plotted against the reaction time.…”

Orientational Behavior and Vibrational Response of Glycine at Aqueous Interfaces

“…It also serves as a major inhibitory neurotransmitter in the spinal cord and the brain stem. , Considering the ubiquitous nature of glycine in biological systems, its physicochemical properties, which govern its biochemical behavior, have been thoroughly studied. Earlier studies investigated its structural and vibrational properties, − and the properties of its aqueous solvation shell − as well as some of its physicochemical properties at water/solid interfaces , and surfactant-covered water/air interfaces. − In addition, the specific interaction between metal ions and carboxylates/glycine has been the subject of numerous studies, − many of which suggest that ion-specific interactions play a significant role. To better understand glycine’s behavior as a neurotransmitter, further studies are required, related to its behavior at aqueous interfaces and in the presence of ions.…”