Salt effects on the picosecond dynamics of lysozyme hydration water investigated by terahertz time-domain spectroscopy and an insight into the Hofmeister series for protein stability and solubility

Abstract

The addition of salts into protein aqueous solutions causes changes in protein solubility and stability, whose ability is known to be ordered in the Hofmeister series. We investigated the effects of Hofmeister salts on the picosecond dynamics of water around a lysozyme molecule using terahertz time-domain spectroscopy. The change in the absorption coefficient for 200 mg mL(-1) lysozyme aqueous solution by the addition of salts was found to depend on the salts used, whereas that for pure water was almost independent of salts. From the difference in the salt concentration dependence for various salts, it has been found that chaotropic anions make the dynamics of water around the lysozyme molecule slower, whereas kosmotropic anions make the dynamics faster. The ability of an anion to slow down the water dynamics was found to have the following order: SCN(-) > Cl(-) > H2PO4(-) > NO3(-) ≈ SO4(2-). This result indicates that the effects of anions on the dynamics of water around the lysozyme molecule are the opposite of those for bulk water. This finding agrees with a prediction from a molecular model proposed by Collins [K. D. Collins, Methods, 2004, 34, 300]. The results presented here are compared with the results from preferential interaction studies and the results from sum frequency generation spectroscopy. These discussions have led to the conclusion that the picosecond dynamics of protein hydration water strongly contributes to protein stability, whereas electrostatic interactions between protein molecules contribute to protein solubility.

Evaluation of crystal quality of thin protein crystals based on the dynamical theory of X-ray diffraction

“…Recently, it has been reported that the crystal quality of hen egg-white lysozyme (HEWL) crystals is improved when the concentration of the precipitant in growth solution is higher (Koizumi et al, 2019). This is attributed to the faster dynamics of water around the protein molecules (Koizumi et al, 2019;Aoki et al, 2013Aoki et al, , 2016. However, the quality might be inferior to that of GI crystals since the oscillatory profiles of rocking curves by dynamical diffraction has not been observed yet.…”

Do soft anions promote protein denaturation through binding interactions? A case study using ribonuclease A

“…9,33,40 Measurements of protein stability have shown that the so anions thiocyanate, iodide and bromide signicantly destabilize the folded state of protein. 9,[41][42][43][44][45] At a rst glance, it may seem logical to interpret the effects of these so ions in terms of their interaction with aliphatic hydrocarbon, aromatic hydrocarbon and polar amide surfaces; however, a series of elegant studies on model polypeptides that combined thermodynamic, spectroscopic and theoretical approaches call this interpretation into question. [46][47][48][49] These studies have clearly shown that: (a) thiocyanate, iodide and bromide can bind directly to CH and CH 2 groups that are adjacent to electron-withdrawing moieties (e.g., alpha carbons on the polypeptide backbone), 46,48 suggesting that the partitioning of these ions in the near vicinity of these groups should be different from what is observed elsewhere on the hydrophobic surface; (b) these binding interactions are strong enough to measurably inhibit the thermally induced aggregation of these model polypeptides.…”

Cancellation between auto- and mutual correlation contributions of protein/water dynamics in terahertz time-domain spectra

“…As a result of technical advances in generating and detecting pulsed radiation in the terahertz region, terahertz time-domain spectroscopy has been widely conducted on bimolecular systems [14][15][16][17][18][19][20][21]. Terahertz time-domain spectra (THz-TDS) studies of proteins in solution have shown that water perturbs the protein dynamics via its hydrogen bond network by both direct short-range interactions in the first hydration shell and indirect long-range interactions up to several hydration shells [17][18][19].…”