Ageing and vision: structure, stability and function of lens crystallins.
ABSTRACT The alpha-, beta- and gamma-crystallins are the major protein components of the vertebrate eye lens, alpha-crystallin as a molecular chaperone as well as a structural protein, beta- and gamma-crystallins as structural proteins. For the lens to be able to retain life-long transparency in the absence of protein turnover, the crystallins must meet not only the requirement of solubility associated with high cellular concentration but that of longevity as well. For proteins, longevity is commonly assumed to be correlated with long-term retention of native structure, which in turn can be due to inherent thermodynamic stability, efficient capture and refolding of non-native protein by chaperones, or a combination of both. Understanding how the specific interactions that confer intrinsic stability of the protein fold are combined with the stabilizing effect of protein assembly, and how the non-specific interactions and associations of the assemblies enable the generation of highly concentrated solutions, is thus of importance to understand the loss of transparency of the lens with age. Post-translational modification can have a major effect on protein stability but an emerging theme of the few studies of the effect of post-translational modification of the crystallins is one of solubility and assembly. Here we review the structure, assembly, interactions, stability and post-translational modifications of the crystallins, not only in isolation but also as part of a multi-component system. The available data are discussed in the context of the establishment, the maintenance and finally, with age, the loss of transparency of the lens. Understanding the structural basis of protein stability and interactions in the healthy eye lens is the route to solve the enormous medical and economical problem of cataract.
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ABSTRACT: Background Cataract is the leading cause of blindness, especially in the developing world. To ease access to treatment, we have proposed that cataract could be treated non-invasively by photobleaching of the chemically modified proteins responsible for cataract formation. The present study was aimed at examining the optical and biochemical effects of the proposed treatment.Methods Human donor lenses were photobleaced using a 445 nm cw laser. Lens optical quality was assessed before and after photobleaching by light transmission and scattering. The concentration of the advanced glycation end products (AGEs) pentosidine, argpyrimidine, carboxymethyllysine, hydroimidazolone was measured.ResultsTransmission increased and AGE-related fluorescence decreased significantly after photobleaching but no changes were observed in the concentration of the measured AGEs.Conclusions We found a significant effect of the photobleaching treatment on lens optical parameters but we could not associate the optical findings to a change in the concentration of the AGEs we measured. This finding suggests that other AGEs were responsible for the observed photobleaching of the human lens after laser treatment. The biochemical nature of the photochemical reactions associated with photobleaching remains to be elucidated.BMC Research Notes 01/2015; 8(1):5. DOI:10.1186/s13104-015-0977-3
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ABSTRACT: MALDI imaging requires careful sample preparation to obtain reliable, high-quality images of small molecules, peptides, lipids, and proteins across tissue sections. Poor crystal formation, delocalization of analytes, and inadequate tissue adherence can affect the quality, reliability, and spatial resolution of MALDI images. We report a comparison of tissue mounting and washing methods that resulted in an optimized method using conductive carbon substrates that avoids thaw mounting or washing steps, minimizes protein delocalization, and prevents tissue detachment from the target surface. Application of this method to image ocular lens proteins of small vertebrate eyes demonstrates the improved methodology for imaging abundant crystallin protein products. This method was demonstrated for tissue sections from rat, mouse, and zebrafish lenses resulting in good-quality MALDI images with little to no delocalization. The images indicate, for the first time in mouse and zebrafish, discrete localization of crystallin protein degradation products resulting in concentric rings of distinct protein contents that may be responsible for the refractive index gradient of vertebrate lenses.Analytical and Bioanalytical Chemistry 02/2015; 407(8). DOI:10.1007/s00216-015-8489-5 · 3.58 Impact Factor
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ABSTRACT: Water homeostasis and the structural integrity of the vertebrate lens is partially mediated by AQP0 channels. Emerging evidence indicates that external pH may be involved in channel gating. Here we show that a tetraploid teleost, the Atlantic salmon, retains 4 aqp0 genes (aqp0a1, -0a2, -0b1, and -0b2), which are highly, but not exclusively, expressed in the lens. Functional characterization reveals that, although each paralog permeates water efficiently, the permeability is respectively shifted to the neutral, alkaline, or acidic pH in Aqp0a1, -0a2, and -0b1, whereas that of Aqp0b2 is not regulated by external pH. Mutagenesis studies demonstrate that Ser(38), His(39), and His(40) residues in the extracellular transmembrane domain of α-helix 2 facing the water pore are critical for the pH modulation of water transport. To validate these findings, we show that both zebrafish Aqp0a and -0b are functional water channels with respective pH sensitivities toward alkaline or acid pH ranges and that an N-terminal allelic variant (Ser(19)) of Aqp0b exists that abolishes water transport in Xenopus laevis oocytes. The data suggest that the alkaline pH sensitivity is a conserved trait in teleost Aqp0 a-type channels, whereas mammalian AQP0 and some teleost Aqp0 b-type channels display an acidic pH permeation preference.-Chauvigné, F., Zapater, C., Stavang, J. A., Taranger, G. L., Cerdà, J., finn, R. N. The pH sensitivity of Aqp0 channels in tetraploid and diploid teleosts. © FASEB.The FASEB Journal 02/2015; DOI:10.1096/fj.14-267625 · 5.48 Impact Factor