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Fujii N, Takata T, Kim I, Morishima K, Inoue R, Magami K, Matsubara T, Sugiyama M, Koide T. Asp isomerization increases aggregation of α-crystallin and decreases its chaperone activity in human lens of various ages. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2020; 1868:140446. [PMID: 32442520 DOI: 10.1016/j.bbapap.2020.140446] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2020] [Revised: 05/12/2020] [Accepted: 05/14/2020] [Indexed: 10/24/2022]
Abstract
α-Crystallin, comprising 40-50 subunits of αA- and αB-subunits, is a long-lived major soluble chaperone protein in lens. During aging, α-crystallin forms aggregates of high molecular weight (HMW) protein and eventually becomes water-insoluble (WI). Isomerization of Asp in α-crystallin has been proposed as a trigger of protein aggregation, ultimately leading to cataract formation. Here, we have investigated the relationship between protein aggregation and Asp isomerization of αA-crystallin by a series of analyses of the soluble α-crystallin, HMW and WI fractions from human lens samples of different ages (10-76 years). Analytical ultracentrifugation showed that the HMW fraction had a peak sedimentation coefficient of 40 S and a wide distribution of values (10-450 S) for lens of all ages, whereas the α-crystallin had a much smaller peak sedimentation coefficient (10-20 S) and was less heterogeneous, regardless of lens age. Measurement of the ratio of isomers (Lα-, Lβ-, Dα-, Dβ-) at Asp58, Asp91/92 and Asp151 in αA-crystallin by liquid chromatography-mass spectrometry showed that the proportion of isomers at all three sites increased in order of aggregation level (α-crystallin < HMW < WI fractions). Among the abnormal isomers of Asp58 and Asp151, Dβ-isomers were predominant with a very few exceptions. Notably, the chaperone activity of HMW protein was minimal for lens of all ages, whereas that of α-crystallin decreased with increasing lens age. Thus, abnormal aggregation caused by Asp isomerization might contribute to the loss of chaperone activity of α-crystallin in aged human lens.
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Affiliation(s)
- Noriko Fujii
- Institute for Integrated Radiation and Nuclear Science, Kyoto University Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan.
| | - Takumi Takata
- Institute for Integrated Radiation and Nuclear Science, Kyoto University Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan
| | - Ingu Kim
- Institute for Integrated Radiation and Nuclear Science, Kyoto University Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan
| | - Ken Morishima
- Institute for Integrated Radiation and Nuclear Science, Kyoto University Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan
| | - Rintaro Inoue
- Institute for Integrated Radiation and Nuclear Science, Kyoto University Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan
| | - Kousuke Magami
- Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
| | | | - Masaaki Sugiyama
- Institute for Integrated Radiation and Nuclear Science, Kyoto University Kumatori-cho, Sennan-gun, Osaka 590-0494, Japan
| | - Tamaki Koide
- Rexxam Co., Ltd., Nishi-ku, Nagoya, Aichi 541-0054, Japan
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Nandi SK, Nahomi RB, Rankenberg J, Glomb MA, Nagaraj RH. Glycation-mediated inter-protein cross-linking is promoted by chaperone-client complexes of α-crystallin: Implications for lens aging and presbyopia. J Biol Chem 2020; 295:5701-5716. [PMID: 32184356 PMCID: PMC7186181 DOI: 10.1074/jbc.ra120.012604] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2020] [Revised: 03/12/2020] [Indexed: 12/16/2022] Open
Abstract
Lens proteins become increasingly cross-linked through nondisulfide linkages during aging and cataract formation. One mechanism that has been implicated in this cross-linking is glycation through formation of advanced glycation end products (AGEs). Here, we found an age-associated increase in stiffness in human lenses that was directly correlated with levels of protein-cross-linking AGEs. α-Crystallin in the lens binds to other proteins and prevents their denaturation and aggregation through its chaperone-like activity. Using a FRET-based assay, we examined the stability of the αA-crystallin-γD-crystallin complex for up to 12 days and observed that this complex is stable in PBS and upon incubation with human lens-epithelial cell lysate or lens homogenate. Addition of 2 mm ATP to the lysate or homogenate did not decrease the stability of the complex. We also generated complexes of human αA-crystallin or αB-crystallin with alcohol dehydrogenase or citrate synthase by applying thermal stress. Upon glycation under physiological conditions, the chaperone-client complexes underwent greater extents of cross-linking than did uncomplexed protein mixtures. LC-MS/MS analyses revealed that the levels of cross-linking AGEs were significantly higher in the glycated chaperone-client complexes than in glycated but uncomplexed protein mixtures. Mouse lenses subjected to thermal stress followed by glycation lost resilience more extensively than lenses subjected to thermal stress or glycation alone, and this loss was accompanied by higher protein cross-linking and higher cross-linking AGE levels. These results uncover a protein cross-linking mechanism in the lens and suggest that AGE-mediated cross-linking of α-crystallin-client complexes could contribute to lens aging and presbyopia.
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Affiliation(s)
- Sandip K Nandi
- Sue Anschutz-Rodgers Eye Center and Department of Ophthalmology, School of Medicine, University of Colorado, Aurora, Colorado 80045
| | - Rooban B Nahomi
- Sue Anschutz-Rodgers Eye Center and Department of Ophthalmology, School of Medicine, University of Colorado, Aurora, Colorado 80045
| | - Johanna Rankenberg
- Sue Anschutz-Rodgers Eye Center and Department of Ophthalmology, School of Medicine, University of Colorado, Aurora, Colorado 80045
| | - Marcus A Glomb
- Institute of Chemistry-Food Chemistry, Martin-Luther-University Halle-Wittenberg, 06120 Halle/Saale, Germany
| | - Ram H Nagaraj
- Sue Anschutz-Rodgers Eye Center and Department of Ophthalmology, School of Medicine, University of Colorado, Aurora, Colorado 80045; Department of Pharmaceutical Sciences, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of Colorado, Aurora, Colorado 80045.
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Takata T, Ha S, Koide T, Fujii N. Site-specific rapid deamidation and isomerization in human lens αA-crystallin in vitro. Protein Sci 2020; 29:955-965. [PMID: 31930615 PMCID: PMC7096717 DOI: 10.1002/pro.3821] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2019] [Revised: 12/27/2019] [Accepted: 12/27/2019] [Indexed: 12/16/2022]
Abstract
Recent studies have suggested that the isomerization/racemization of aspartate residues in proteins increases in aged tissues. One such residue is Asp151 in lens-specific αA-crystallin. Although many isomerization/racemization sites have been reported in various proteins, the factors that lead to those modifications in proteins in vivo remain obscure. Therefore, an in vitro system is needed to assess the mechanisms of modifications of Asp under various conditions. Deamidation of Asn to Asp in proteins occurs more rapidly than isomerization/racemization of Asp, although the reaction passes through the same intermediate in both pathways. Here, therefore, we replaced Asp151 in human lens αA-crystallin with Asn by using site-directed mutagenesis. The recombinant protein was expressed in Escherichia coli and used to investigate the deamidation/isomerization/racemization of Asn151 after incubation at 50°C for various durations and under different pH. After incubation, the mutant αA-crystallin was subjected to enzymatic digestion followed by liquid chromatography-MS/MS to evaluate the ratio of modifications in Asn151-containing peptides. The Asp151Asn αA-crystallin mutant showed rapid deamidation to Asp with the formation of specific Asp isomers. In particular, deamidation increased greatly under basic conditions. By contrast, subunit-subunit interactions between αA-crystallin and αB-crystallin had little effect on the modification of Asn151. Our findings suggest that the Asp151Asn αA-crystallin mutant represents a good in vitro model protein to assess deamidation, isomerization, and the racemization intermediates. Furthermore, our in vitro results show a different trend from in vivo data, implying the presence of specific factors that induce racemization from L-Asp to D-Asp residues in vivo.
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Affiliation(s)
- Takumi Takata
- Kyoto University Institute for Integrated Radiation and Nuclear ScienceOsakaJapan
| | - Seongmin Ha
- Department of ChemistryGraduate School of Science, Kyoto UniversityKyotoJapan
| | | | - Noriko Fujii
- Kyoto University Institute for Integrated Radiation and Nuclear ScienceOsakaJapan
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Takata T, Matsubara T, Nakamura-Hirota T, Fujii N. Negative charge at aspartate 151 is important for human lens αA-crystallin stability and chaperone function. Exp Eye Res 2019; 182:10-18. [PMID: 30849387 DOI: 10.1016/j.exer.2019.02.023] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2018] [Revised: 01/21/2019] [Accepted: 02/28/2019] [Indexed: 01/18/2023]
Abstract
Aggregation of lens protein is a major cause of senile cataract. Lens crystallins contain many kinds of modification that accumulate over lifespan. In particular, isomerization of Asp 151 in αA-crystallin has been found in aged lenses; however, its significance is unknown. The purpose of this study was to determine the effects of isomerization of Asp 151 in αA-crystallin. Trypsin digestion followed by liquid chromatography-mass spectrometry analysis of the water-soluble high molecular weight (HMW) fraction from human lens samples showed that isomerization of Asp 151 in αA-crystallin is age-independent, and that 50% of isomerization occurs shortly after birth. However, the extent of Asp 151 isomerization varied with the size of αA-crystallin oligomer species separated from the HMW fraction from aged lens. To evaluate the effects of modification, Asp 151 of αA-crystallin was replaced by glycine, alanine, isoleucine, asparagine, glutamate, or lysine by site-directed mutagenesis. All substitutions except for glutamate decreased heat stability and chaperone function as compared with wild-type αA-crystallin. In particular, abnormal hydrophobicity and alteration of the charge state at Asp 151 caused loss of stability and chaperone activity of αA-crystallin; these properties were recovered to some extent when the mutant protein was mixed 1:1 with wild-type αA-crystallin. The results suggest that, by itself, age-independent isomerization of Asp 151 in αA-crystallin may not contribute to cataract formation. However, the long-term deleterious effect of Asp 151 isomerization on the structure and function of αA-crystallin might cooperatively contribute to the loss of transparency of aged human lens.
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Affiliation(s)
- Takumi Takata
- Institute for Integrated Radiation and Nuclear Science, Kyoto University, Kumatori-cho, Sennan-gun, Osaka, 590-0494, Japan
| | | | | | - Noriko Fujii
- Institute for Integrated Radiation and Nuclear Science, Kyoto University, Kumatori-cho, Sennan-gun, Osaka, 590-0494, Japan.
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