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Vendra VPR, Khan I, Chandani S, Muniyandi A, Balasubramanian D. Gamma crystallins of the human eye lens. Biochim Biophys Acta Gen Subj 2015; 1860:333-43. [PMID: 26116913 DOI: 10.1016/j.bbagen.2015.06.007] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2015] [Revised: 06/08/2015] [Accepted: 06/19/2015] [Indexed: 01/12/2023]
Abstract
BACKGROUND Protein crystallins co me in three types (α, β and γ) and are found predominantly in the eye, and particularly in the lens, where they are packed into a compact, plastic, elastic, and transparent globule of proper refractive power range that aids in focusing incoming light on to the retina. Of these, the γ-crystallins are found largely in the nuclear region of the lens at very high concentrations (>400 mg/ml). The connection between their structure and inter-molecular interactions and lens transparency is an issue of particular interest. SCOPE OF REVIEW We review the origin and phylogeny of the gamma crystallins, their special structure involving the use of Greek key supersecondary structural motif, and how they aid in offering the appropriate refractive index gradient, intermolecular short range attractive interactions (aiding in packing them into a transparent ball), the role that several of the constituent amino acid residues play in this process, the thermodynamic and kinetic stability and how even single point mutations can upset this delicate balance and lead to intermolecular aggregation, forming light-scattering particles which compromise transparency. We cite several examples of this, and illustrate this by cloning, expressing, isolating and comparing the properties of the mutant protein S39C of human γS-crystallin (associated with congenital cataract-microcornea), with those of the wild type molecule. In addition, we note that human γ-crystallins are also present in other parts of the eye (e.g., retina), where their functions are yet to be understood. MAJOR CONCLUSIONS There are several 'crucial' residues in and around the Greek key motifs which are essential to maintain the compact architecture of the crystallin molecules. We find that a mutation that replaces even one of these residues can lead to reduction in solubility, formation of light-scattering particles and loss of transparency in the molecular assembly. GENERAL SIGNIFICANCE Such a molecular understanding of the process helps us construct the continuum of genotype-molecular structural phenotype-clinical (pathological) phenotype. This article is part of a Special Issue entitled Crystallin Biochemistry in Health and Disease.
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Affiliation(s)
- Venkata Pulla Rao Vendra
- Ophthalmic Molecular Genetics Section, National Eye Institute, Building 5635FL, Room 1S24, 5625 Fishers Lane, Rockville, MD 20852, United States.
| | - Ismail Khan
- Prof. Brien Holden Eye Research Centre, Hyderabad Eye Research Foundation, L. V. Prasad Eye Institute, Hyderabad 500034 Telangana, India.
| | - Sushil Chandani
- Plot 32, LIC Colony, W Marredpally, Secunderabad 500026, Telangana, India.
| | - Anbukkarasi Muniyandi
- Department of Animal Science, Bharathidasan University, Tiruchirappalli 620 024, Tamil Nadu, India.
| | - Dorairajan Balasubramanian
- Prof. Brien Holden Eye Research Centre, Hyderabad Eye Research Foundation, L. V. Prasad Eye Institute, Hyderabad 500034 Telangana, India.
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Kingsley CN, Bierma JC, Pham V, Martin RW. γS-crystallin proteins from the Antarctic nototheniid toothfish: a model system for investigating differential resistance to chemical and thermal denaturation. J Phys Chem B 2014; 118:13544-53. [PMID: 25372016 PMCID: PMC4254003 DOI: 10.1021/jp509134d] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
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The γS1- and γS2-crystallins,
structural eye lens proteins
from the Antarctic toothfish (Dissostichus mawsoni), are homologues of the human lens protein γS-crystallin.
Although γS1 has the higher thermal stability of the two, it
is more susceptible to chemical denaturation by urea. The lower thermodynamic
stability of both toothfish crystallins relative to human γS-crystallin
is consistent with the current picture of how proteins from organisms
endemic to perennially cold environments have achieved low-temperature
functionality via greater structural flexibility. In some respects,
the sequences of γS1- and γS2-crystallin are typical of
psychrophilic proteins; however, their amino acid compositions also
reflect their selection for a high refractive index increment. Like
their counterparts in the human lens and those of mesophilic fish,
both toothfish crystallins are relatively enriched in aromatic residues
and methionine and exiguous in aliphatic residues. The sometimes contradictory
requirements of selection for cold tolerance and high refractive index
make the toothfish crystallins an excellent model system for further
investigation of the biophysical properties of structural proteins.
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Affiliation(s)
- Carolyn N Kingsley
- Department of Chemistry, University of California-Irvine , 1102 Natural Sciences 2, Irvine, California, 92697-2025, United States
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Slingsby C, Wistow GJ. Functions of crystallins in and out of lens: roles in elongated and post-mitotic cells. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2014; 115:52-67. [PMID: 24582830 PMCID: PMC4104235 DOI: 10.1016/j.pbiomolbio.2014.02.006] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/02/2014] [Accepted: 02/18/2014] [Indexed: 12/25/2022]
Abstract
The vertebrate lens evolved to collect light and focus it onto the retina. In development, the lens grows through massive elongation of epithelial cells possibly recapitulating the evolutionary origins of the lens. The refractive index of the lens is largely dependent on high concentrations of soluble proteins called crystallins. All vertebrate lenses share a common set of crystallins from two superfamilies (although other lineage specific crystallins exist). The α-crystallins are small heat shock proteins while the β- and γ-crystallins belong to a superfamily that contains structural proteins of uncertain function. The crystallins are expressed at very high levels in lens but are also found at lower levels in other cells, particularly in retina and brain. All these proteins have plausible connections to maintenance of cytoplasmic order and chaperoning of the complex molecular machines involved in the architecture and function of cells, particularly elongated and post-mitotic cells. They may represent a suite of proteins that help maintain homeostasis in such cells that are at risk from stress or from the accumulated insults of aging.
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Affiliation(s)
- Christine Slingsby
- Department of Biological Sciences, Crystallography, Institute of Structural and Molecular Biology, Birkbeck College, Malet Street, London WC1E 7HX, UK.
| | - Graeme J Wistow
- Section on Molecular Structure and Functional Genomics, National Eye Institute, Bg 6, Rm 106, National Institutes of Health, Bethesda, MD 20892-0608, USA
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54
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Primary sequence contribution to the optical function of the eye lens. Sci Rep 2014; 4:5195. [PMID: 24903231 PMCID: PMC4047532 DOI: 10.1038/srep05195] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2014] [Accepted: 04/17/2014] [Indexed: 01/28/2023] Open
Abstract
The crystallins have relatively high refractive increments compared to other proteins. The Greek key motif in βγ-crystallins was compared with that in other proteins, using predictive analysis from a protein database, to see whether this may be related to the refractive increment. Crystallins with Greek keys motifs have significantly higher refractive increments and more salt bridges than other proteins with Greek key domains. Specific amino acid substitutions: lysine and glutamic acid residues are replaced by arginine and aspartic acid, respectively as refractive increment increases. These trends are also seen in S-crystallins suggesting that the primary sequence of crystallins may be specifically enriched with amino acids with appropriate values of refractive increment to meet optical requirements. Comparison of crystallins from five species: two aquatic and three terrestrial shows that the lysine/arginine correlation with refractive increment occurs in all species investigated. This may be linked with formation and maintenance of salt bridges.
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Serebryany E, King JA. The βγ-crystallins: native state stability and pathways to aggregation. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2014; 115:32-41. [PMID: 24835736 DOI: 10.1016/j.pbiomolbio.2014.05.002] [Citation(s) in RCA: 74] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/05/2014] [Revised: 04/30/2014] [Accepted: 05/02/2014] [Indexed: 01/26/2023]
Abstract
The βγ-crystallins are among the most stable and long-lived proteins in the human body. With increasing age, however, they transform to high molecular weight light-scattering aggregates, resulting in cataracts. This occurs despite the presence in the lens of high concentrations of the a-crystallin chaperones. Aggregation of crystallins can be induced in vitro by a variety of stresses, including acidic pH, ultraviolet light, oxidative damage, heating or freezing, and specific amino acid substitutions. Accumulating evidence points to the existence of specific biochemical pathways of protein: protein interaction and polymerization. We review the methods used for studying crystallin stability and aggregation and discuss the sometimes counterintuitive relationships between factors that favor native state stability and those that favor non-native aggregation. We discuss the behavior of βγ-crystallins in mixtures and their chaperone ability; the consequences of missense mutations and covalent damage to the side-chains; and the evolutionary strategies that have shaped these proteins. Efforts are ongoing to reveal the nature of cataractous crystallin aggregates and understand the mechanisms of aggregation in the context of key models of protein polymerization: amyloid, native-state, and domain-swapped. Such mechanistic understanding is likely to be of value for the development of therapeutic interventions and draw attention to unanswered questions about the relationship between a protein's native state stability and its transformation to an aggregated state.
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Affiliation(s)
- Eugene Serebryany
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, United States
| | - Jonathan A King
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA, United States.
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Chen Y, Zhao H, Schuck P, Wistow G. Solution properties of γ-crystallins: compact structure and low frictional ratio are conserved properties of diverse γ-crystallins. Protein Sci 2013; 23:76-87. [PMID: 24214907 DOI: 10.1002/pro.2395] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2013] [Revised: 10/29/2013] [Accepted: 10/31/2013] [Indexed: 11/11/2022]
Abstract
γ-crystallins are highly specialized proteins of the vertebrate eye lens where they survive without turnover under high molecular crowding while maintaining transparency. They share a tightly folded structural template but there are striking differences among species. Their amino acid compositions are unusual. Even in mammals, γ-crystallins have high contents of sulfur-containing methionine and cysteine, but this reaches extremes in fish γM-crystallins with up to 15% Met. In addition, fish γM-crystallins do not conserve the paired tryptophan residues found in each domain in mammalian γ-crystallins and in the related β-crystallins. To gain insight into important, evolutionarily conserved properties and functionality of γ-crystallins, zebrafish (Danio rerio) γM2b and γM7 were compared with mouse γS and human γD. For all four proteins, far UV CD spectra showed the expected β-sheet secondary structure. Like the mammalian proteins, γM7 was highly soluble but γM2b was much less so. The heat and denaturant stability of both fish proteins was lower than either mammalian protein. The ability of full-length and truncated versions of human αB-crystallin to retard aggregation of the heat denatured proteins also showed differences. However, when solution behavior was investigated by sedimentation velocity experiments, the diverse γ-crystallins showed remarkably similar hydrodynamic properties with low frictional ratios and partial specific volumes. The solution behavior of γ-crystallins, with highly compact structures suited for the densely packed environment of the lens, seems to be highly conserved and appears largely independent of amino acid composition.
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Affiliation(s)
- Yingwei Chen
- Section on Molecular Structure and Functional Genomics, National Eye Institute, National Institutes of Health, Bethesda, Maryland, 20892-0608
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57
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Zhao H, Chen Y, Rezabkova L, Wu Z, Wistow G, Schuck P. Solution properties of γ-crystallins: hydration of fish and mammal γ-crystallins. Protein Sci 2013; 23:88-99. [PMID: 24282025 DOI: 10.1002/pro.2394] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2013] [Revised: 10/30/2013] [Accepted: 10/31/2013] [Indexed: 11/06/2022]
Abstract
Lens γ crystallins are found at the highest protein concentration of any tissue, ranging from 300 mg/mL in some mammals to over 1000 mg/mL in fish. Such high concentrations are necessary for the refraction of light, but impose extreme requirements for protein stability and solubility. γ-crystallins, small stable monomeric proteins, are particularly associated with the lowest hydration regions of the lens. Here, we examine the solvation of selected γ-crystallins from mammals (human γD and mouse γS) and fish (zebrafish γM2b and γM7). The thermodynamic water binding coefficient B₁ could be probed by sucrose expulsion, and the hydrodynamic hydration shell of tightly bound water was probed by translational diffusion and structure-based hydrodynamic boundary element modeling. While the amount of tightly bound water of human γD was consistent with that of average proteins, the water binding of mouse γS was found to be relatively low. γM2b and γM7 crystallins were found to exhibit extremely low degrees hydration, consistent with their role in the fish lens. γM crystallins have a very high methionine content, in some species up to 15%. Structure-based modeling of hydration in γM7 crystallin suggests low hydration is associated with the large number of surface methionine residues, likely in adaptation to the extremely high concentration and low hydration environment in fish lenses. Overall, the degree of hydration appears to balance stability and tissue density requirements required to produce and maintain the optical properties of the lens in different vertebrate species.
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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, Bethesda, Maryland, 20892
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Ribeiro A, Matamá T, Cruz CF, Gomes AC, Cavaco-Paulo AM. Potential of human γD-crystallin for hair damage repair: insights into the mechanical properties and biocompatibility. Int J Cosmet Sci 2013; 35:458-66. [PMID: 23651449 DOI: 10.1111/ics.12065] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2013] [Accepted: 05/02/2013] [Indexed: 11/29/2022]
Abstract
OBJECTIVES The objective of this work was to develop a new strategy to physically 'repair' chemically damaged hair. Hence the human eye γD-crystallin, a protein from the superfamily characterized structurally by the Greek key motif, was studied. The human γD-crystallin was chosen based on the ability of proteins belonging to this superfamily to be involved in the coating of specific structures. Two crystallins were used on the study, the wild type (Protein Data Bank ID: 1HK0) and the mutant protein. The mutant form was intended to induce a strong and quick protein polymerization as well to have new possible points of anchorage to hair. METHODS The ability of both crystallins to bind to damaged hair and even penetrate into its cortex was checked by fluorescence microscopy, confocal microscopy and scanning electron microscopy. Furthermore the reinforcement of hair mechanical resistance, the potential cytotoxic/inflammatory effect of crystallins were studied in order to have a fully comprehension about the protein based formulation. RESULTS Although the chemical over-bleaching treatment induced a decrease of 20% on the resistance of the hair, the crystallins which bind and penetrate the hair fibre were able to recover and even to improve its mechanical properties when compared to the virgin hair. Moreover none of the crystallins displayed a toxic effect in fibroblasts for all the range of tested concentrations upon 72 h of exposure. The active aggregation process of mutant crystallin induced an inflammatory response in fibroblasts in the first 24 h of contact, measured by the amount of released pro-inflammatory cytokine IL-6 to the medium. In contrast contact with wild type crystallin did not lead to significant inflammation. CONCLUSION Outcome from protein formulation characterization supports the hypothesis that the γD-crystallin it is able to recover and improve the mechanical properties of chemical damaged hair. Therefore it can be considered as a very promising strengthening agent for the development of new restorative hair care products.
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Affiliation(s)
- A Ribeiro
- IBB-Institute for Biotechnology and Bioengineering, Centre of Biological Engineering, Universidade do Minho, Campus de Gualtar, 4710-057, Braga, Portugal; Department of Biology, Centre of Molecular and Environmental Biology (CBMA), Universidade do Minho, Campus de Gualtar, 4710-057, Braga, Portugal
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59
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Mahler B, Chen Y, Ford J, Thiel C, Wistow G, Wu Z. Structure and dynamics of the fish eye lens protein, γM7-crystallin. Biochemistry 2013; 52:3579-87. [PMID: 23597261 DOI: 10.1021/bi400151c] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The vertebrate eye lens contains high concentrations of crystallins. The dense lenses of fish are particularly abundant in a class called γM-crystallin whose members are characterized by an unusually high methionine content and partial loss of the four tryptophan residues conserved in all γ-crystallins from mammals which are proposed to contribute to protection from UV-damage. Here, we present the structure and dynamics of γM7-crystallin from zebrafish (Danio rerio). The solution structure shares the typical two-domain, four-Greek-key motif arrangement of other γ-crystallins, with the major difference noted in the final loop of the N-terminal domain, spanning residues 65-72. This is likely due to the absence of the conserved tryptophans. Many of the methionine residues are exposed on the surface but are mostly well-ordered and frequently have contacts with aromatic side chains. This may contribute to the specialized surface properties of these proteins that exist under high molecular crowding in the fish lens. NMR relaxation data show increased backbone conformational motions in the loop regions of γM7 compared to those of mouse γS-crystallin and show that fast internal motion of the interdomain linker in γ-crystallins correlates with linker length. Unfolding studies monitored by tryptophan fluorescence confirm results from mutant mouse γS-crystallin and show that unfolding of a βγ-crystallin domain likely starts from unfolding of the variable loop containing the more fluorescently quenched tryptophan residue, resulting in a native-like unfolding intermediate.
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Affiliation(s)
- Bryon Mahler
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
| | - Yingwei Chen
- Section on Molecular Structure and Function, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892, United States
| | - Jason Ford
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
| | - Caleb Thiel
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
| | - Graeme Wistow
- Section on Molecular Structure and Function, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892, United States
| | - Zhengrong Wu
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
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Slingsby C, Wistow GJ, Clark AR. Evolution of crystallins for a role in the vertebrate eye lens. Protein Sci 2013; 22:367-80. [PMID: 23389822 PMCID: PMC3610043 DOI: 10.1002/pro.2229] [Citation(s) in RCA: 105] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Revised: 01/16/2013] [Accepted: 01/17/2013] [Indexed: 12/18/2022]
Abstract
The camera eye lens of vertebrates is a classic example of the re-engineering of existing protein components to fashion a new device. The bulk of the lens is formed from proteins belonging to two superfamilies, the α-crystallins and the βγ-crystallins. Tracing their ancestry may throw light on the origin of the optics of the lens. The α-crystallins belong to the ubiquitous small heat shock proteins family that plays a protective role in cellular homeostasis. They form enormous polydisperse oligomers that challenge modern biophysical methods to uncover the molecular basis of their assembly structure and chaperone-like protein binding function. It is argued that a molecular phenotype of a dynamic assembly suits a chaperone function as well as a structural role in the eye lens where the constraint of preventing protein condensation is paramount. The main cellular partners of α-crystallins, the β- and γ-crystallins, have largely been lost from the animal kingdom but the superfamily is hugely expanded in the vertebrate eye lens. Their structures show how a simple Greek key motif can evolve rapidly to form a complex array of monomers and oligomers. Apart from remaining transparent, a major role of the partnership of α-crystallins with β- and γ-crystallins in the lens is to form a refractive index gradient. Here, we show some of the structural and genetic features of these two protein superfamilies that enable the rapid creation of different assembly states, to match the rapidly changing optical needs among the various vertebrates.
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Affiliation(s)
- Christine Slingsby
- Department of Biological Sciences, Crystallography, Institute of Structural and Molecular Biology, Birkbeck College, Malet Street, London WC1E 7HX, United Kingdom.
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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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