Abstract
We present a multiscale characterization of aqueous solutions of the bovine eye lens protein βH crystallin from dilute conditions up to dynamical arrest, combining dynamic light scattering, small-angle x-ray scattering, tracer-based microrheology, and neutron spin echo spectroscopy. We obtain a comprehensive explanation of the observed experimental signatures from a model of polydisperse hard spheres with additional weak attraction. In particular, the model predictions quantitatively describe the multiscale dynamical results from microscopic nanometer cage diffusion over mesoscopic micrometer gradient diffusion up to macroscopic viscosity. Based on a comparative discussion with results from other crystallin proteins, we suggest an interesting common pathway for dynamical arrest in all crystallin proteins, with potential implications for the understanding of crowding effects in the eye lens.
Highlights
The intracellular fluid within fiber cells in the eye lens is composed of a dense solution of mainly proteins from the crystallin family
We studied the emerging effects on dynamics in crowded and nearly arrested solutions reaching from the local level (NSE) over the density-gradient scale (DLS) to macroscopic relaxation
Structural aspects could not be reproduced in full quantitative detail but follow the expected trends, we obtain a very good description of dynamics from the local nanometer scale of cage diffusion to a mesoscopic micrometer scale of gradient diffusion to the macroscopic scale of viscosity
Summary
The intracellular fluid within fiber cells in the eye lens is composed of a dense solution of mainly proteins from the crystallin family This crowded solution with up to 400 mg/mL protein content has fascinating properties, ensuring a large enough refractive index, transparency, and flexibility of the lens required for visual function and stability over the mammalian lifetime. Crowding affects a large range of properties, including inter alia structural stability, reaction equilibria, and long-range self-diffusion [4,5,6], but a conclusive picture on underlying mechanisms could not yet be obtained. This lack is linked to the necessity of obtaining a comprehensive multiscale picture to relate macroscopic phenomenology to microscopic mechanisms. Microscopic mechanisms were studied in more detail in model systems, outlining, e.g., the importance of self-association for resulting dynamical properties [7,8], the relevance of translational-rotational coupling [9], and the Biophysical Journal 119, 2483–2496, December 15, 2020 2483
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