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Regini JW, Yagi N, Young RD, Tanioka H, Kinoshita S, Hoshino M, Uesugi K, Meek KM, Augousti AT, Knupp C, Pierscionek BK, Quantock AJ, Elliott GF. Membrane structures and functional correlates in the bi-segmented eye lens of the cephalopod. Biol Open 2024; 13:bio060445. [PMID: 39133170 PMCID: PMC11381927 DOI: 10.1242/bio.060445] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2024] [Accepted: 07/31/2024] [Indexed: 08/13/2024] Open
Abstract
The cephalopod eye lens is unique because it has evolved as a compound structure with two physiologically distinct segments. However, the detailed ultrastructure of this lens and precise optical role of each segment are far from clear. To help elucidate structure-function relationships in the cephalopod lens, we conducted multiple structural investigations on squid. Synchrotron x-ray scattering and transmission electron microscopy disclose that an extensive network of structural features that resemble cell membrane complexes form a substantial component of both anterior and posterior lens segments. Optically, the segments are distinct, however, and Talbot interferometry indicates that the posterior segment possesses a noticeably higher refractive index gradient. We propose that the hitherto unrecognised network of membrane structures in the cephalopod lens has evolved to act as an essential conduit for the internal passage of ions and other metabolic agents through what is otherwise a highly dense structure owing to a very high protein concentration.
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Affiliation(s)
- Justyn W Regini
- Structural Biophysics Group, Cardiff Centre for Vision Science, School of Optometry and Vision Sciences, Cardiff University, Maindy Road, Cardiff, CF24 4HQ, Wales, UK
| | - Naoto Yagi
- SPring-8, Japan Synchrotron Radiation Research Institute, 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5198Japan
| | - Robert D Young
- Structural Biophysics Group, Cardiff Centre for Vision Science, School of Optometry and Vision Sciences, Cardiff University, Maindy Road, Cardiff, CF24 4HQ, Wales, UK
| | - Hidetoshi Tanioka
- Department of Ophthalmology, Kyoto Prefectural University of Medicine, Hirokoji Kawaramachi, Kyoto, 602-0841, Japan
| | - Shigeru Kinoshita
- Department of Ophthalmology, Kyoto Prefectural University of Medicine, Hirokoji Kawaramachi, Kyoto, 602-0841, Japan
| | - Masato Hoshino
- SPring-8, Japan Synchrotron Radiation Research Institute, 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5198Japan
| | - Kentaro Uesugi
- SPring-8, Japan Synchrotron Radiation Research Institute, 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5198Japan
| | - Keith M Meek
- Structural Biophysics Group, Cardiff Centre for Vision Science, School of Optometry and Vision Sciences, Cardiff University, Maindy Road, Cardiff, CF24 4HQ, Wales, UK
| | - Andy T Augousti
- Faculty of Science, Engineering and Computing, Kingston University London, Friars Avenue, London SW15, UK
| | - Carlo Knupp
- Structural Biophysics Group, Cardiff Centre for Vision Science, School of Optometry and Vision Sciences, Cardiff University, Maindy Road, Cardiff, CF24 4HQ, Wales, UK
| | - Barbara K Pierscionek
- Faculty of Health Medicine and Social Care, Medical Technology Research Centre, Anglia Ruskin University, Bishop Hall Lane, Chelmsford CM1 1SQ, UK
| | - Andrew J Quantock
- Structural Biophysics Group, Cardiff Centre for Vision Science, School of Optometry and Vision Sciences, Cardiff University, Maindy Road, Cardiff, CF24 4HQ, Wales, UK
| | - Gerald F Elliott
- Structural Biophysics Group, Cardiff Centre for Vision Science, School of Optometry and Vision Sciences, Cardiff University, Maindy Road, Cardiff, CF24 4HQ, Wales, UK
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Bergman MR, Hernandez SA, Deffler C, Yeo J, Deravi LF. Design and Characterization of Model Systems that Promote and Disrupt Transparency of Vertebrate Crystallins In Vitro. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2023; 10:e2303279. [PMID: 37897315 PMCID: PMC10724405 DOI: 10.1002/advs.202303279] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2023] [Revised: 08/31/2023] [Indexed: 10/30/2023]
Abstract
Positioned within the eye, the lens supports vision by transmitting and focusing light onto the retina. As an adaptive glassy material, the lens is constituted primarily by densely-packed, polydisperse crystallin proteins that organize to resist aggregation and crystallization at high volume fractions, yet the details of how crystallins coordinate with one another to template and maintain this transparent microstructure remain unclear. The role of individual crystallin subtypes (α, β, and γ) and paired subtype compositions, including how they experience and resist crowding-induced turbidity in solution, is explored using combinations of spectrophotometry, hard-sphere simulations, and surface pressure measurements. After assaying crystallin combinations, β-crystallins emerged as a principal component in all mixtures that enabled dense fluid-like packing and short-range order necessary for transparency. These findings helped inform the design of lens-like hydrogel systems, which are used to monitor and manipulate the loss of transparency under different crowding conditions. When taken together, the findings illustrate the design and characterization of adaptive materials made from lens proteins that can be used to better understand mechanisms regulating transparency.
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Affiliation(s)
- Michael R. Bergman
- Department of Chemistry and Chemical BiologyNortheastern University360 Huntington AveBostonMA02115USA
| | - Sophia A. Hernandez
- Department of Chemistry and Chemical BiologyNortheastern University360 Huntington AveBostonMA02115USA
| | - Caitlin Deffler
- Department of Chemistry and Chemical BiologyNortheastern University360 Huntington AveBostonMA02115USA
| | - Jingjie Yeo
- Sibley School of Mechanical and Aerospace EngineeringCornell University413 Upson Hall, 124 Hoy RdIthacaNY14850USA
| | - Leila F. Deravi
- Department of Chemistry and Chemical BiologyNortheastern University360 Huntington AveBostonMA02115USA
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Muranov KO, Ostrovsky MA. Biochemistry of Eye Lens in the Norm and in Cataractogenesis. BIOCHEMISTRY. BIOKHIMIIA 2022; 87:106-120. [PMID: 35508906 DOI: 10.1134/s0006297922020031] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2021] [Revised: 09/30/2021] [Accepted: 09/30/2021] [Indexed: 06/14/2023]
Abstract
The absence of cellular organelles in fiber cells and very high cytoplasmic protein concentration (up to 900 mg/ml) minimize light scattering in the lens and ensure its transparency. Low oxygen concentration, powerful defense systems (antioxidants, antioxidant enzymes, chaperone-like protein alpha-crystallin, etc.) maintain lens transparency. On the other hand, the ability of crystallins to accumulate age-associated post-translational modifications, which reduce the resistance of lens proteins to oxidative stress, is an important factor contributing to the cataract formation. Here, we suggest a mechanism of cataractogenesis common for the action of different cataractogenic factors, such as age, radiation, ultraviolet light, diabetes, etc. Exposure to these factors leads to the damage and death of lens epithelium, which allows oxygen to penetrate into the lens through the gaps in the epithelial layer and cause oxidative damage to crystallins, resulting in protein denaturation, aggregation, and formation of multilamellar bodies (the main cause of lens opacification). The review discusses various approaches to the inhibition of lens opacification (cataract development), in particular, a combined use of antioxidants and compounds enhancing the chaperone-like properties of alpha-crystallin. We also discuss the paradox of high efficiency of anti-cataract drugs in laboratory settings with the lack of their clinical effect, which might be due to the late use of the drugs at the stage, when the opacification has already formed. A probable solution to this situation will be development of new diagnostic methods that will allow to predict the emergence of cataract long before the manifestation of its clinical signs and to start early preventive treatment.
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Affiliation(s)
- Konstantin O Muranov
- Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Moscow, 119334, Russia.
| | - Mikhail A Ostrovsky
- Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, Moscow, 119334, Russia
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4
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Imbalances in the eye lens proteome are linked to cataract formation. Nat Struct Mol Biol 2021; 28:143-151. [PMID: 33432246 DOI: 10.1038/s41594-020-00543-9] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2020] [Accepted: 11/04/2020] [Indexed: 01/29/2023]
Abstract
The prevalent model for cataract formation in the eye lens posits that damaged crystallin proteins form light-scattering aggregates. The α-crystallins are thought to counteract this process as chaperones by sequestering misfolded crystallin proteins. In this scenario, chaperone pool depletion would result in lens opacification. Here we analyze lenses from different mouse strains that develop early-onset cataract due to point mutations in α-, β-, or γ-crystallin proteins. We find that these mutant crystallins are unstable in vitro; in the lens, their levels are substantially reduced, and they do not accumulate in the water-insoluble fraction. Instead, all the other crystallin proteins, including the α-crystallins, are found to precipitate. The changes in protein composition and spatial organization of the crystallins observed in the mutant lenses suggest that the imbalance in the lenticular proteome and altered crystallin interactions are the bases for cataract formation, rather than the aggregation propensity of the mutant crystallins.
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Muranov KO, Poliansky NB, Kleimenov SY, Ostrovsky MA. Chaperone-Like Protein a-Crystallin Brakes the Aggregation but Does Not Support Refolding of UV-Damaged βL-Crystallin. RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY B 2020. [DOI: 10.1134/s1990793119060253] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Muranov KO, Poliansky NB, Chebotareva NA, Kleimenov SY, Bugrova AE, Indeykina MI, Kononikhin AS, Nikolaev EN, Ostrovsky MA. The mechanism of the interaction of α-crystallin and UV-damaged β L-crystallin. Int J Biol Macromol 2019; 140:736-748. [PMID: 31445149 DOI: 10.1016/j.ijbiomac.2019.08.178] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2019] [Revised: 08/18/2019] [Accepted: 08/20/2019] [Indexed: 12/24/2022]
Abstract
α-Crystallin maintains the transparency of the lens by preventing the aggregation of damaged proteins. The aim of our work was to study the chaperone-like activity of native α-crystallin in near physiological conditions (temperature, ionic power, pH) using UV-damaged βL-crystallin as the target protein. α-Crystallin in concentration depended manner inhibits the aggregation of UV-damaged βL-crystallin. DSC investigation has shown that refolding of denatured UV-damaged βL-crystallin was not observed under incubation with α-crystallin. α-Crystallin and UV-damaged βL-crystallin form dynamic complexes with masses from 75 to several thousand kDa. The content of UV-damaged βL-crystallin in such complexes increases with the mass of the complex. Complexes containing >10% of UV-damaged βL-crystallin are prone to precipitation whereas those containing <10% of the target protein are relatively stable. Formation of a stable 75 kDa complex is indicative of α-crystallin dissociation. We suppose that α-crystallin dissociation is the result of an interaction of comparable amounts of the chaperone-like protein and the target protein. In the lens simultaneous damage of such amounts of protein, mainly β and gamma-crystallins, is impossible. The authors suggest that in the lens rare molecules of the damaged protein interact with undissociated oligomers of α-crystallin, and thus preventing aggregation.
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Affiliation(s)
- K O Muranov
- Emanuel Institute of Biochemical Physics of the Russian Academy of Sciences, Moscow, Russia.
| | - N B Poliansky
- Emanuel Institute of Biochemical Physics of the Russian Academy of Sciences, Moscow, Russia
| | - N A Chebotareva
- Bach Institute of Biochemistry, Federal State Institution "Federal Research Centre "Fundamentals of Biotechnology"of the Russian Academy of Sciences", Moscow, Russia
| | - S Yu Kleimenov
- Koltzov Institute of Developmental Biology of the Russian Academy of Sciences, Russia
| | - A E Bugrova
- Emanuel Institute of Biochemical Physics of the Russian Academy of Sciences, Moscow, Russia
| | - M I Indeykina
- Emanuel Institute of Biochemical Physics of the Russian Academy of Sciences, Moscow, Russia; Talrose Institute for Energy Problems of Chemical Physics, Semenov Federal Center of Chemical Physic, Russian Academy of Sciences, Moscow, Russia
| | - A S Kononikhin
- Talrose Institute for Energy Problems of Chemical Physics, Semenov Federal Center of Chemical Physic, Russian Academy of Sciences, Moscow, Russia; Skolkovo Institute of Science and Technology, Skolkovo, Russia
| | - E N Nikolaev
- Talrose Institute for Energy Problems of Chemical Physics, Semenov Federal Center of Chemical Physic, Russian Academy of Sciences, Moscow, Russia; Skolkovo Institute of Science and Technology, Skolkovo, Russia
| | - M A Ostrovsky
- Emanuel Institute of Biochemical Physics of the Russian Academy of Sciences, Moscow, Russia
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3D structure of the native α-crystallin from bovine eye lens. Int J Biol Macromol 2018; 117:1289-1298. [PMID: 29870813 DOI: 10.1016/j.ijbiomac.2018.06.004] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2018] [Accepted: 06/01/2018] [Indexed: 12/30/2022]
Abstract
α-Crystallin is the major eye lens protein that has been shown to support lens transparency by preventing the aggregation of lens proteins. The 3D structure of α-crystallin is largely unknown. Electron microscopy, single-particle 3D reconstruction, size exclusion chromatography, dynamic light scattering, and analytical ultracentrifugation were used to study the structure of the native α-crystallin. Native α-crystallin has a wide distribution in size. The shape of mass distribution is temperature-dependent, but the oligomers with a sedimentation coefficient of ~22 S (750-830 kDa) strongly prevailed at all temperatures used. A 3D model of native α-crystallin with resolution of ~2 nm was created. The model is asymmetrical, has an elongated bean-like shape 13 × 19 nm with a dense core and filamentous "kernel". It does not contain a central cavity. The majority of α-crystallin particles regardless of experimental conditions are 13 × 19 nm, which corresponds to 22S sedimentation coefficient, hydrodynamic diameter 20 nm and mass of 750-830 kD. These particles are in dynamic equilibrium with particles of smaller and larger sizes.
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Harden JL, Guo H, Bertrand M, Shendruk TN, Ramakrishnan S, Leheny RL. Enhanced gel formation in binary mixtures of nanocolloids with short-range attraction. J Chem Phys 2018; 148:044902. [DOI: 10.1063/1.5007038] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- James L. Harden
- Department of Physics, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada
| | - Hongyu Guo
- Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - Martine Bertrand
- Department of Physics, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada
| | - Tyler N. Shendruk
- Center for Studies in Physics and Biology, The Rockefeller University, 1230 York Avenue, New York, New York 10065, USA
| | - Subramanian Ramakrishnan
- Department of Chemical and Biomedical Engineering, FAMU-FSU College of Engineering, Tallahassee, Florida 32312, USA
| | - Robert L. Leheny
- Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA
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Barnes S, Quinlan RA. Small molecules, both dietary and endogenous, influence the onset of lens cataracts. Exp Eye Res 2016; 156:87-94. [PMID: 27039707 DOI: 10.1016/j.exer.2016.03.024] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Revised: 03/18/2016] [Accepted: 03/28/2016] [Indexed: 12/11/2022]
Abstract
How the lens ages successfully is a lesson in biological adaption and the emergent properties of its complement of cells and proteins. This living tissue contains some of the oldest proteins in our bodies and yet they remain functional for decades, despite exposure to UV light, to reactive oxygen species and all the other hazards to protein function. This remarkable feat is achieved by a shrewd investment in very stable proteins as lens crystallins, by providing a reservoir of ATP-independent protein chaperones unequalled by any other tissue and by an oxidation-resistant environment. In addition, glutathione, a free radical scavenger, is present in mM concentrations and the plasma membranes contain oxidation-resistant sphingolipids what compromises lens function as it ages? In this review, we examine the role of small molecules in the prevention or causation of cataracts, including those associated with diet, metabolic pathways and drug therapy (steroids).
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Affiliation(s)
- Stephen Barnes
- Department of Pharmacology and Toxicology, University of Alabama at Birmingham, Birmingham, AL 35294, USA
| | - Roy A Quinlan
- Biophysical Sciences Institute, University of Durham, Durham DH1 3LE, UK; University of Durham, Durham DH1 3LE, UK.
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Lampi KJ, Murray MR, Peterson MP, Eng BS, Yue E, Clark AR, Barbar E, David LL. Differences in solution dynamics between lens β-crystallin homodimers and heterodimers probed by hydrogen-deuterium exchange and deamidation. Biochim Biophys Acta Gen Subj 2015; 1860:304-14. [PMID: 26145577 DOI: 10.1016/j.bbagen.2015.06.014] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2015] [Revised: 06/12/2015] [Accepted: 06/18/2015] [Indexed: 11/28/2022]
Abstract
BACKGROUND Lens transparency is due to the ordered arrangement of the major structural proteins, called crystallins. βB2 crystallin in the lens of the eye readily forms dimers with other β-crystallin subunits, but the resulting heterodimer structures are not known and were investigated in this study. METHODS Structures of βA3 and βB2 crystallin homodimers and the βA3/βB2 crystallin heterodimers were probed by measuring changes in solvent accessibility using hydrogen-deuterium exchange with mass spectrometry. We further mimicked deamidation in βB2 and probed the effect on the βA3/βB2 heterodimer. Results were confirmed with chemical crosslinking and NMR. RESULTS Both βA3 and βB2 had significantly decreased deuterium levels in the heterodimer compared to their respective homodimers, suggesting that they had less solvent accessibility and were more compact in the heterodimer. The compact structure of βB2 was supported by the identification of chemical crosslinks between lysines in βB2 within the heterodimer that were inconsistent with βB2's extended homodimeric structure. The compact structure of βA3 was supported by an overall decrease in mobility of βA3 in the heterodimer detected by NMR. In βB2, peptides 70-84 and 121-134 were exposed in the homodimer, but buried in the heterodimer with ≥50% decreases in deuterium levels. Homologous peptides in βA3, 97-109 and 134-149, had 25-50% decreases in deuterium levels in the heterodimer. These peptides are probable sites of interaction between βB2 and βA3 and are located at the predicted interface between subunits with bent linkers. Deamidation at Q184 in βB2 at this predicted interface led to a less compact βB2 in the heterodimer. The more compact structure of the βA3/βB2 heterodimer was also more heat stable than either of the homodimers. CONCLUSIONS The major structural proteins in the lens, the β-crystallins, are not static, but dynamic in solution, with differences in accessibility between the homo-and hetero-dimers. This structural flexibility, particularly of βB2, may facilitate formation of different size higher-ordered structures found in the transparent lens. GENERAL SIGNIFICANCE Understanding complex hetero-oligomer interactions between β-crystallins in normal lens and how these interactions change during aging is fundamental to understanding the cause of cataracts. This article is part of a Special Issue entitled Crystallin Biochemistry in Health and Disease.
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Affiliation(s)
- Kirsten J Lampi
- Integrative Biosciences, Oregon Health & Science University, Portland, OR 97239-3098, United States.
| | - Matthew R Murray
- Integrative Biosciences, Oregon Health & Science University, Portland, OR 97239-3098, United States
| | - Matthew P Peterson
- Integrative Biosciences, Oregon Health & Science University, Portland, OR 97239-3098, United States
| | - Bryce S Eng
- Integrative Biosciences, Oregon Health & Science University, Portland, OR 97239-3098, United States
| | - Eileen Yue
- Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, OR 97239-3098, United States
| | - Alice R Clark
- Birkbeck College, University of London, United Kingdom
| | - Elisar Barbar
- Biochemistry and Biophysics, Oregon State University, Corvallis, OR 97331, United States
| | - Larry L David
- Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, OR 97239-3098, United States
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Haslbeck M, Peschek J, Buchner J, Weinkauf S. Structure and function of α-crystallins: Traversing from in vitro to in vivo. Biochim Biophys Acta Gen Subj 2015; 1860:149-66. [PMID: 26116912 DOI: 10.1016/j.bbagen.2015.06.008] [Citation(s) in RCA: 74] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2015] [Revised: 06/10/2015] [Accepted: 06/22/2015] [Indexed: 12/11/2022]
Abstract
BACKGROUND The two α-crystallins (αA- and αB-crystallin) are major components of our eye lenses. Their key function there is to preserve lens transparency which is a challenging task as the protein turnover in the lens is low necessitating the stability and longevity of the constituent proteins. α-Crystallins are members of the small heat shock protein family. αB-crystallin is also expressed in other cell types. SCOPE OF THE REVIEW The review summarizes the current concepts on the polydisperse structure of the α-crystallin oligomer and its chaperone function with a focus on the inherent complexity and highlighting gaps between in vitro and in vivo studies. MAJOR CONCLUSIONS Both α-crystallins protect proteins from irreversible aggregation in a promiscuous manner. In maintaining eye lens transparency, they reduce the formation of light scattering particles and balance the interactions between lens crystallins. Important for these functions is their structural dynamics and heterogeneity as well as the regulation of these processes which we are beginning to understand. However, currently, it still remains elusive to which extent the in vitro observed properties of α-crystallins reflect the highly crowded situation in the lens. GENERAL SIGNIFICANCE Since α-crystallins play an important role in preventing cataract in the eye lens and in the development of diverse diseases, understanding their mechanism and substrate spectra is of importance. To bridge the gap between the concepts established in vitro and the in vivo function of α-crystallins, the joining of forces between different scientific disciplines and the combination of diverse techniques in hybrid approaches are necessary. This article is part of a Special Issue entitled Crystallin Biochemistry in Health and Disease.
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Affiliation(s)
- Martin Haslbeck
- Center for Integrated Protein Science at the Department Chemie, Technische Universität München, Lichtenbergstr. 4, D-85747 Garching, Germany
| | - Jirka Peschek
- Center for Integrated Protein Science at the Department Chemie, Technische Universität München, Lichtenbergstr. 4, D-85747 Garching, Germany
| | - Johannes Buchner
- Center for Integrated Protein Science at the Department Chemie, Technische Universität München, Lichtenbergstr. 4, D-85747 Garching, Germany.
| | - Sevil Weinkauf
- Center for Integrated Protein Science at the Department Chemie, Technische Universität München, Lichtenbergstr. 4, D-85747 Garching, Germany.
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Jiao J, Miao A, Zhang X, Cai Y, Lu Y, Zhang Y, Lu H. Realization of on-tissue protein identification by highly efficient in situ digestion with graphene-immobilized trypsin for MALDI imaging analysis. Analyst 2013; 138:1645-8. [DOI: 10.1039/c3an36391k] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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13
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The gradient index lens of the eye: an opto-biological synchrony. Prog Retin Eye Res 2012; 31:332-49. [PMID: 22465790 DOI: 10.1016/j.preteyeres.2012.03.001] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2011] [Revised: 03/02/2012] [Accepted: 03/04/2012] [Indexed: 11/22/2022]
Abstract
The refractive power of a lens is determined largely by its surface curvatures and the refractive index of its medium. These properties can also be used to control the sharpness of focus and hence the image quality. One of the most effective ways of doing this is with a gradient index. Eye lenses of all species, thus far, measured, are gradient index (GRIN) structures. The index gradation is one that increases from the periphery of the lens to its centre but the steepness of the gradient and the magnitudes of the refractive index vary so that the optics of the lens accords with visual demands. The structural proteins, the crystallins, which create the index gradient, also vary from species to species, in type and relative distribution across the tissue. The crystallin classes do not contribute equally to the refractive index, and this may be related to their structure and amino acid content. This article compares GRIN forms in eye lenses of varying species, the relevance of these forms to visual requirements, and the relationship between refractive index and the structural proteins. Consideration is given to the dynamics of a living lens, potential variations in the GRIN form with physiological changes and the possible link between discontinuities in the gradient and growth. Finally, the property of birefringence and the characteristic polarisation patterns seen in highly ordered crystals that have also been observed in specially prepared eye lenses are described and discussed.
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Zhao H, Magone MT, Schuck P. The role of macromolecular crowding in the evolution of lens crystallins with high molecular refractive index. Phys Biol 2011; 8:046004. [PMID: 21566271 DOI: 10.1088/1478-3975/8/4/046004] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Crystallins are present in the lens at extremely high concentrations in order to provide transparency and generate a high refractive power of the lens. The crystallin families prevalent in the highest density lens tissues are γ-crystallins in vertebrates and S-crystallins in cephalopods. As shown elsewhere, in parallel evolution, both have evolved molecular refractive index increments 5-10% above those of most proteins. Although this is a small increase, it is statistically very significant and can be achieved only by very unusual amino acid compositions. In contrast, such a molecular adaptation to aid in the refractive function of the lens did not occur in crystallins that are preferentially located in lower density lens tissues, such as vertebrate α-crystallin and taxon-specific crystallins. In the current work, we apply a model of non-interacting hard spheres to examine the thermodynamic contributions of volume exclusion at lenticular protein concentrations. We show that the small concentration decrease afforded by the higher molecular refractive index increment of crystallins can amplify nonlinearly to produce order of magnitude differences in chemical activities, and lead to reduced osmotic pressure and the reduced propensity for protein aggregation. Quantitatively, this amplification sets in only at protein concentrations as high as those found in hard lenses or the nucleus of soft lenses, in good correspondence to the observed crystallin properties in different tissues and different species. This suggests that volume exclusion effects provide the evolutionary driving force for the unusual refractive properties and the unusual amino acid compositions of γ-crystallins and S-crystallins.
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Affiliation(s)
- Huaying Zhao
- Dynamics of Macromolecular Assembly Section, Laboratory of Cellular Imaging and Macromolecular Biophysics, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD 20892, USA
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15
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Comparative analysis of crystallins and lipids from the lens of Antarctic toothfish and cow. J Comp Physiol B 2010; 180:1019-32. [DOI: 10.1007/s00360-010-0475-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2010] [Revised: 04/12/2010] [Accepted: 04/23/2010] [Indexed: 10/19/2022]
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