Crowding in the Eye Lens: Modeling the Multisubunit Protein β-Crystallin with a Colloidal Approach

Abstract

We present a multiscale characterization of aqueous solutions of the bovine eye lens protein β H 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.

Concentration and temperature dependent interactions and state diagram of dispersions of copolymer microgels

“…Thus, the anomalous feature of S(Q) having the main peak below 1 is the result of the combination of the Hertzian model and the large polydispersity of the system, as also discussed in the ESI. † It is important to note that similar behaviors of S(Q) at high concentrations have been previously reported for polydisperse eye-lens proteins 79 and also, for anisotropic antibodies. 80 It remains to be investigated in the present systems whether such features hold at high f, where steeper excluded volume effects may enter into play and prevent the softening related to the Hertzian modeling.…”

Design and Characterization of Model Systems that Promote and Disrupt Transparency of Vertebrate Crystallins In Vitro

“…[ 41 , 42 ] Hard sphere simulations of α‐crystallins and β‐crystallins were previously used to describe the conditions needed to induce dynamical arrest, i.e., when particles effectively stop motion, observed in experimental studies. [ 43 , 44 , 45 ] To build on this, we utilized the concentration ratios of crystallins that were previously determined in bovine lens [ 46 ] along with average diameters measured with DLS (Figure S2 , Supporting Information) to construct the particle compositions in the simulations.…”

“…[ 25 ] Unlike the squid lens, the vertebrate lens must adopt separate mechanisms to achieve this function by coordinating three crystallin subtypes, with various oligomerization states that are expected to behave as hard spheres based on experimental evidence, [ 16 , 18 , 26 ] and supported by theory. [ 27 ] The maintenance of crystallin solubility under the crowded conditions of the vertebrate lens has puzzled researchers for decades. Are these products of excluded volume that are stabilized by electrostatics, [ 28 ] or are specific interactions between crystallin subtypes regulating this process?…”

Proposed Role for Internal Lens Pressure as an Initiator of Age-Related Lens Protein Aggregation Diseases

“…47,48 PTMs lead to presbyopia and cataract. 49 The major lens PTMs include disulfide bonding, methionine oxidation, deamidation, phosphorylation, and proteolysis. 20,48,[50][51][52][53] Deamidation is a chemical reaction in which an amide group in the side chain of amino acids asparagine or glutamine is removed or converted to another functional group.…”