Stability of Protein-Specific Hydration Shell on Crowding

Abstract

We demonstrate that the effect of protein crowding is critically dependent on the stability of the protein's hydration shell, which can dramatically vary between different proteins. In the human eye lens, γS-crystallin (γS-WT) forms a densely packed transparent hydrogel with a high refractive index, making it an ideal system for studying the effects of protein crowding. A single point mutation generates the cataract-related variant γS-G18V, dramatically altering the optical properties of the eye lens. This system offers an opportunity to explore fundamental questions regarding the effect of protein crowding, using γS-WT and γS-G18V: (i) how do the diffusion dynamics of hydration water change as a function of protein crowding?; and (ii) upon hydrogel formation of γS-WT, has a dynamic transition occurred generating a single population of hydration water, or do populations of bulk and hydration water coexist? Using localized spin probes, we separately probe the local translational diffusivity of both surface hydration and interstitial water of γS-WT and γS-G18V in solution. Surprisingly, we find that under the influence of hydrogel formation at highly crowded γS-WT concentrations up to 500 mg/mL, the protein hydration shell remains remarkably dynamic, slowing by less than a factor of 2, if at all, compared to that in dilute protein solutions of ∼5 mg/mL. Upon self-crowding, the population of this robust surface hydration water increases, while a significant bulk-like water population coexists even at ∼500 mg/mL protein concentrations. In contrast, surface water of γS-G18V irreversibly dehydrates with moderate concentration increases or subtle alterations to the solution conditions, demonstrating that the effect of protein crowding is highly dependent on the stability of the protein-specific hydration shell. The core function of γS-crystallin in the eye lens may be precisely its capacity to preserve a robust hydration shell, whose stability is abolished by a single G18V mutation.

Crowders and Cosolvents—Major Contributors to the Cellular Milieu and Efficient Means to Counteract Environmental Stresses

“…Those results suggest that the majority of intracellular water may be involved in slow, collective hydration, with only trace amounts of “bulk‐like” water present, despite a 50–70 % water content by volume . However, recent contrary findings by the Han group suggest that the hydration shell and thus the crowding‐induced perturbation may be protein‐specific …”

“…[221] However,r ecent contrary findings by the Han group suggest that the hydration shell and thus the crowding-induced perturbation may be protein-specific. [222] Af urther aspect is the decrease of the water activity due to the highc ontent of biomolecules, osmolytes and salts. [14] For example, as olution with the water activity of 0.95 contains 5-30 wt %c osolventm olecules, depending on the cosolvent used.…”

Collaborative routes to clarifying the murky waters of aqueous supramolecular chemistry

“…In essence, supramolecular chemists have utilized the available tools (those used by synthetic chemists for characterization), not the techniques best suited for a detailed analysis of aqueous supramolecular systems (Table 1). [65][66][67][68] Spectroscopy: Hosts and guests It is hard to beat NMR. In large part its popularity within the supramolecular community arises from its ability to provide high-resolution details of the structural changes accompanying binding.…”

Molecular simulations of cellular processes

“…Albeit popular, Eq. 2 and most treatments of hydrodynamic interactions do not account for the perturbation of the solvent caused by crowding agents (Harada et al 2012;Mukherjee et al 2015;Wang et al 2017b) or by protein-specific effects (Huang et al 2016). …”

“…This often limits the scope of the studies, as it is now well recognized that the cellular environment perturbs the dynamics and thermodynamics of proteins and nucleic acids, as well as the solvent, with consequences on cell physiology (Luby-Phelps 1999; Foffi et al 2013;Mourão et al 2014;Huang et al 2016;Rivas and Minton 2016;Wang et al 2017b) . A factor that has been demonstrated early to modify the activity and mobility of biomolecules in vivo is the concentration of bystander macromolecules, also known as crowders, that can be as high as 40% of the cell volume (Muramatsu and Minton 1988).…”