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O'Neale CV, Tran MH, Schey KL. Aquaporin-0-protein interactions elucidated by crosslinking mass spectrometry. Biochem Biophys Res Commun 2024; 727:150320. [PMID: 38963984 DOI: 10.1016/j.bbrc.2024.150320] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2024] [Revised: 06/12/2024] [Accepted: 06/26/2024] [Indexed: 07/06/2024]
Abstract
Aquaporin-0 (AQP0) constitutes 50 % of the lens membrane proteome and plays important roles in lens fiber cell adhesion, water permeability, and lens transparency. Previous work has shown that specific proteins, such as calmodulin (CaM), interact with AQP0 to modulate its water permeability; however, these studies often used AQP0 peptides, rather than full-length protein, to probe these interactions. Furthermore, the specific regions of interaction of several known AQP0 interacting partners, i.e. αA and αB-crystallins, and phakinin (CP49) remain unknown. The purpose of this study was to use crosslinking mass spectrometry (XL-MS) to identify interacting proteins with full-length AQP0 in crude lens cortical membrane fractions and to determine the specific protein regions of interaction. Our results demonstrate, for the first time, that the AQP0 N-terminus can engage in protein interactions. Specific regions of interaction are elucidated for several AQP0 interacting partners including phakinin, α-crystallin, connexin-46, and connexin-50. In addition, two new interacting partners, vimentin and connexin-46, were identified.
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Affiliation(s)
- Carla Vt O'Neale
- Department of Biochemistry, Vanderbilt University, 465 21(ST), Ave, So. MRB III, Suite 9160, Nashville, TN, 37240, USA
| | - Minh H Tran
- Chemical and Physical Biology Program, 465 21(ST), Ave, So. MRB III, Suite 9160, Vanderbilt University, Nashville, TN, 37240, USA
| | - Kevin L Schey
- Department of Biochemistry, Vanderbilt University, 465 21(ST), Ave, So. MRB III, Suite 9160, Nashville, TN, 37240, USA.
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2
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Tashiro M, Nakamura A, Kuratani Y, Takada M, Iwamoto S, Oka M, Ando S. Effects of truncations in the N- and C-terminal domains of filensin on filament formation with phakinin in cell-free conditions and cultured cells. FEBS Open Bio 2023; 13:1990-2004. [PMID: 37615966 PMCID: PMC10626283 DOI: 10.1002/2211-5463.13700] [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: 05/19/2023] [Revised: 07/27/2023] [Accepted: 08/22/2023] [Indexed: 08/25/2023] Open
Abstract
Filensin and phakinin are lens fiber cell-specific proteins that constitute the beaded filaments (BFs) that are critical for maintaining lens transparency. In the Shumiya cataract rat, filensin 94 kDa undergoes N- and C-terminal proteolytic processing to give a transient 50 kDa fragment and a final 38 kDa fragment, just before opacification. To characterize the effects of this processing on filensin function, recombinant proteins representing the two filensin fragments, termed Fil(30-416) and Fil(30-369), respectively, were examined. Fil(30-416) lacks the N-terminal 29 amino acids and the C-terminal 248 amino acids. Fil(30-369) lacks the N-terminal 29 residues and the C-terminal 295 residues. In cell-free assembly characterized by electron microscopy, filensin and Fil(30-416) co-polymerized with phakinin and formed rugged, entangled filaments, whereas Fil(30-369) formed only aggregates. In cultured SW-13 and MCF-7 cells expressing fluorescent fusion proteins, filensin and Fil(30-416) co-polymerized with phakinin and formed cytoplasmic sinuous filaments with different widths, while Fil(30-369) gave aggregates. Therefore, while truncation of the N-terminal 29 amino acids did not affect filament formation, truncation of the C-terminal 295 but not the 248 residues resulted in failure of filament formation. These results indicate that the tail B region (residues 370-416) of rat filensin is essential for filament formation with phakinin. Truncation of the tail B region by proteolytic processing in the cataract rat lens might interfere with BF formation and thereby contribute to opacification.
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Affiliation(s)
- Moe Tashiro
- Faculty of Biotechnology and Life ScienceSojo UniversityKumamotoJapan
| | - Akari Nakamura
- Faculty of Biotechnology and Life ScienceSojo UniversityKumamotoJapan
| | - Yamato Kuratani
- Faculty of Biotechnology and Life ScienceSojo UniversityKumamotoJapan
| | - Miyako Takada
- Faculty of Biotechnology and Life ScienceSojo UniversityKumamotoJapan
| | - Satoshi Iwamoto
- Faculty of Biotechnology and Life ScienceSojo UniversityKumamotoJapan
| | - Mikako Oka
- Faculty of PharmacyKeio UniversityTokyoJapan
- Present address:
Yokohama University of Pharmacy601 Matano‐cho, Totsuka‐kuYokohama245‐0066Japan
| | - Shoji Ando
- Faculty of Biotechnology and Life ScienceSojo UniversityKumamotoJapan
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3
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Jarrin M, Kalligeraki AA, Uwineza A, Cawood CS, Brown AP, Ward EN, Le K, Freitag-Pohl S, Pohl E, Kiss B, Tapodi A, Quinlan RA. Independent Membrane Binding Properties of the Caspase Generated Fragments of the Beaded Filament Structural Protein 1 (BFSP1) Involves an Amphipathic Helix. Cells 2023; 12:1580. [PMID: 37371051 PMCID: PMC10297038 DOI: 10.3390/cells12121580] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2023] [Revised: 06/04/2023] [Accepted: 06/05/2023] [Indexed: 06/29/2023] Open
Abstract
BACKGROUND BFSP1 (beaded filament structural protein 1) is a plasma membrane, Aquaporin 0 (AQP0/MIP)-associated intermediate filament protein expressed in the eye lens. BFSP1 is myristoylated, a post-translation modification that requires caspase cleavage at D433. Bioinformatic analyses suggested that the sequences 434-452 were α-helical and amphipathic. METHODS AND RESULTS By CD spectroscopy, we show that the addition of trifluoroethanol induced a switch from an intrinsically disordered to a more α-helical conformation for the residues 434-467. Recombinantly produced BFSP1 fragments containing this amphipathic helix bind to lens lipid bilayers as determined by surface plasmon resonance (SPR). Lastly, we demonstrate by transient transfection of non-lens MCF7 cells that these same BFSP1 C-terminal sequences localise to plasma membranes and to cytoplasmic vesicles. These can be co-labelled with the vital dye, lysotracker, but other cell compartments, such as the nuclear and mitochondrial membranes, were negative. The N-terminal myristoylation of the amphipathic helix appeared not to change either the lipid affinity or membrane localisation of the BFSP1 polypeptides or fragments we assessed by SPR and transient transfection, but it did appear to enhance its helical content. CONCLUSIONS These data support the conclusion that C-terminal sequences of human BFSP1 distal to the caspase site at G433 have independent membrane binding properties via an adjacent amphipathic helix.
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Affiliation(s)
- Miguel Jarrin
- Department of Biosciences, Upper Mountjoy Science Site, The University of Durham, South Road, Durham DH1 3LE, UK (R.A.Q.)
- Biophysical Sciences Institute, Durham University, Upper Mountjoy, South Road, Durham DH1 3LE, UK
| | - Alexia A. Kalligeraki
- Department of Biosciences, Upper Mountjoy Science Site, The University of Durham, South Road, Durham DH1 3LE, UK (R.A.Q.)
- Biophysical Sciences Institute, Durham University, Upper Mountjoy, South Road, Durham DH1 3LE, UK
| | - Alice Uwineza
- Department of Biosciences, Upper Mountjoy Science Site, The University of Durham, South Road, Durham DH1 3LE, UK (R.A.Q.)
- Biophysical Sciences Institute, Durham University, Upper Mountjoy, South Road, Durham DH1 3LE, UK
| | - Chris S. Cawood
- Department of Biosciences, Upper Mountjoy Science Site, The University of Durham, South Road, Durham DH1 3LE, UK (R.A.Q.)
- Biophysical Sciences Institute, Durham University, Upper Mountjoy, South Road, Durham DH1 3LE, UK
| | - Adrian P. Brown
- Department of Biosciences, Upper Mountjoy Science Site, The University of Durham, South Road, Durham DH1 3LE, UK (R.A.Q.)
| | - Edward N. Ward
- Department of Biosciences, Upper Mountjoy Science Site, The University of Durham, South Road, Durham DH1 3LE, UK (R.A.Q.)
- Biophysical Sciences Institute, Durham University, Upper Mountjoy, South Road, Durham DH1 3LE, UK
| | - Khoa Le
- Biophysical Sciences Institute, Durham University, Upper Mountjoy, South Road, Durham DH1 3LE, UK
- Department of Biological Structure, University of Washington, Seattle, WA 98195, USA
| | - Stefanie Freitag-Pohl
- Department of Chemistry, Durham University, Lower Mountjoy, South Road, Durham DH1 3LE, UK
| | - Ehmke Pohl
- Biophysical Sciences Institute, Durham University, Upper Mountjoy, South Road, Durham DH1 3LE, UK
- Department of Chemistry, Durham University, Lower Mountjoy, South Road, Durham DH1 3LE, UK
| | - Bence Kiss
- Department of Biochemistry and Medical Chemistry, Medical School, University of Pécs, 7624 Pécs, Hungary
| | - Antal Tapodi
- Department of Biosciences, Upper Mountjoy Science Site, The University of Durham, South Road, Durham DH1 3LE, UK (R.A.Q.)
- Biophysical Sciences Institute, Durham University, Upper Mountjoy, South Road, Durham DH1 3LE, UK
- Department of Biochemistry and Medical Chemistry, Medical School, University of Pécs, 7624 Pécs, Hungary
| | - Roy A. Quinlan
- Department of Biosciences, Upper Mountjoy Science Site, The University of Durham, South Road, Durham DH1 3LE, UK (R.A.Q.)
- Biophysical Sciences Institute, Durham University, Upper Mountjoy, South Road, Durham DH1 3LE, UK
- Department of Biological Structure, University of Washington, Seattle, WA 98195, USA
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Schey KL, Gletten RB, O’Neale CVT, Wang Z, Petrova RS, Donaldson PJ. Lens Aquaporins in Health and Disease: Location is Everything! Front Physiol 2022; 13:882550. [PMID: 35514349 PMCID: PMC9062079 DOI: 10.3389/fphys.2022.882550] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2022] [Accepted: 03/23/2022] [Indexed: 01/07/2023] Open
Abstract
Cataract and presbyopia are the leading cause of vision loss and impaired vision, respectively, worldwide. Changes in lens biochemistry and physiology with age are responsible for vision impairment, yet the specific molecular changes that underpin such changes are not entirely understood. In order to preserve transparency over decades of life, the lens establishes and maintains a microcirculation system (MCS) that, through spatially localized ion pumps, induces circulation of water and nutrients into (influx) and metabolites out of (outflow and efflux) the lens. Aquaporins (AQPs) are predicted to play important roles in the establishment and maintenance of local and global water flow throughout the lens. This review discusses the structure and function of lens AQPs and, importantly, their spatial localization that is likely key to proper water flow through the MCS. Moreover, age-related changes are detailed and their predicted effects on the MCS are discussed leading to an updated MCS model. Lastly, the potential therapeutic targeting of AQPs for prevention or treatment of cataract and presbyopia is discussed.
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Affiliation(s)
- Kevin L. Schey
- Department of Biochemistry, School of Medicine, Vanderbilt University, Nashville, TN, United States,*Correspondence: Kevin L. Schey,
| | - Romell B. Gletten
- Department of Biochemistry, School of Medicine, Vanderbilt University, Nashville, TN, United States
| | - Carla V. T. O’Neale
- Department of Biochemistry, School of Medicine, Vanderbilt University, Nashville, TN, United States
| | - Zhen Wang
- Department of Biochemistry, School of Medicine, Vanderbilt University, Nashville, TN, United States
| | - Rosica S. Petrova
- Department of Physiology, School of Medical Sciences, University of Auckland, Auckland, New Zealand
| | - Paul J. Donaldson
- Department of Physiology, School of Medical Sciences, University of Auckland, Auckland, New Zealand
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Cantrell LS, Schey KL. Proteomic characterization of the human lens and Cataractogenesis. Expert Rev Proteomics 2021; 18:119-135. [PMID: 33849365 DOI: 10.1080/14789450.2021.1913062] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
INTRODUCTION The goal of this review is to highlight the triumphs and frontiers in measurement of the lens proteome as it relates to onset of age-related nuclear cataract. As global life expectancy increases, so too does the frequency of age-related nuclear cataracts. Molecular therapeutics do not exist for delay or relief of cataract onset in humans. Since lens fiber cells are incapable of protein synthesis after initial maturation, age-related changes in proteome composition and post-translational modification accumulation can be measured with various techniques. Several of these modifications have been associated with cataract onset. AREAS COVERED We discuss the impact of long-lived proteins on the lens proteome and lens homeostasis as well as proteomic techniques that may be used to measure proteomes at various levels of proteomic specificity and spatial resolution. EXPERT OPINION There is clear evidence that several proteome modifications are correlated with cataract formation. Past studies should be enhanced with cutting-edge, spatially resolved mass spectrometry techniques to enhance the specificity and sensitivity of modification detection as it relates to cataract formation.
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Affiliation(s)
- Lee S Cantrell
- Department of Biochemistry, Vanderbilt University, Nashville, TN, United States
| | - Kevin L Schey
- Department of Biochemistry, Vanderbilt University, Nashville, TN, United States
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Wang Z, Ryan DJ, Schey KL. Localization of the lens intermediate filament switch by imaging mass spectrometry. Exp Eye Res 2020; 198:108134. [PMID: 32682822 PMCID: PMC7508834 DOI: 10.1016/j.exer.2020.108134] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2020] [Revised: 06/07/2020] [Accepted: 06/29/2020] [Indexed: 01/18/2023]
Abstract
Imaging mass spectrometry (IMS) enables targeted and untargeted visualization of the spatial localization of molecules in tissues with great specificity. The lens is a unique tissue that contains fiber cells corresponding to various stages of differentiation that are packed in a highly spatial order. The application of IMS to lens tissue localizes molecular features that are spatially related to the fiber cell organization. Such spatially resolved molecular information assists our understanding of lens structure and physiology; however, protein IMS studies are typically limited to abundant, soluble, low molecular weight proteins. In this study, a method was developed for imaging low solubility cytoskeletal proteins in the lens; a tissue that is filled with high concentrations of soluble crystallins. Optimized tissue washes combined with on-tissue enzymatic digestion allowed successful imaging of peptides corresponding to known lens cytoskeletal proteins. The resulting peptide signals facilitated segmentation of the bovine lens into molecularly distinct regions. A sharp intermediate filament transition from vimentin to lens-specific beaded filament proteins was detected in the lens cortex. MALDI IMS also revealed the region where posttranslational myristoylation of filensin occurs and the results indicate that truncation and myristoylation of filensin starts soon after filensin expression increased in the inner cortex. From intermediate filament switch to filensin truncation and myristoylation, multiple remarkable changes occur in the narrow region of lens cortex. MALDI images delineated the boundaries of distinct lens regions that will guide further proteomic and interactomic studies.
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Affiliation(s)
- Zhen Wang
- Department of Biochemistry, Vanderbilt University, Nashville, TN 37232, USA
| | - Daniel J Ryan
- Department of Biochemistry, Vanderbilt University, Nashville, TN 37232, USA
| | - Kevin L Schey
- Department of Biochemistry, Vanderbilt University, Nashville, TN 37232, USA.
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7
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Schey KL, Wang Z, Friedrich MG, Garland DL, Truscott RJW. Spatiotemporal changes in the human lens proteome: Critical insights into long-lived proteins. Prog Retin Eye Res 2019; 76:100802. [PMID: 31704338 DOI: 10.1016/j.preteyeres.2019.100802] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2019] [Revised: 10/24/2019] [Accepted: 10/30/2019] [Indexed: 12/15/2022]
Abstract
The ocular lens is a unique tissue that contains an age gradient of cells and proteins ranging from newly differentiated cells containing newly synthesized proteins to cells and proteins that are as old as the organism. Thus, the ocular lens is an excellent model for studying long-lived proteins (LLPs) and the effects of aging and post-translational modifications on protein structure and function. Given the architecture of the lens, with young fiber cells in the outer cortex and the oldest cells in the lens nucleus, spatially-resolved studies provide information on age-specific protein changes. In this review, experimental strategies and proteomic methods that have been used to examine age-related and cataract-specific changes to the human lens proteome are described. Measured spatio-temporal changes in the human lens proteome are summarized and reveal a highly consistent, time-dependent set of modifications observed in transparent human lenses. Such measurements have led to the discovery of cataract-specific modifications and the realization that many animal systems are unsuitable to study many of these modifications. Mechanisms of protein modifications such as deamidation, racemization, truncation, and protein-protein crosslinking are presented and the implications of such mechanisms for other long-lived proteins in other tissues are discussed in the context of age-related neurological diseases. A comprehensive understanding of LLP modifications will enhance our ability to develop new therapies for the delay, prevention or reversal of age-related diseases.
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Affiliation(s)
- Kevin L Schey
- Department of Biochemistry, Vanderbilt University, USA.
| | - Zhen Wang
- Department of Biochemistry, Vanderbilt University, USA
| | - Michael G Friedrich
- Illawarra Health and Medical Research Institute, University of Wollongong, Australia
| | | | - Roger J W Truscott
- Illawarra Health and Medical Research Institute, University of Wollongong, Australia
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8
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Varadaraj K, Kumari S. Deletion of Seventeen Amino Acids at the C-Terminal End of Aquaporin 0 Causes Distortion Aberration and Cataract in the Lenses of AQP0ΔC/ΔC Mice. Invest Ophthalmol Vis Sci 2019; 60:858-867. [PMID: 30821811 PMCID: PMC6397018 DOI: 10.1167/iovs.18-26378] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Purpose Investigate the effects of the absence of 17 amino acids at the C-terminal end of Aquaporin 0 (AQP0) on lens transparency, focusing property, and homeostasis. Methods A knockin (KI) mouse model (AQP0ΔC/ΔC) was developed to express AQP0 only as the end-cleaved form in the lens. For this, AQP0 was genetically engineered as C-terminally end-cleaved with amino acids 1 to 246, instead of the full length 1 to 263 of the wild type (WT). After verifying the KI integration into the genome and its expression, the mouse model was bred for several generations. AQP0 KI homozygous (AQP0ΔC/ΔC) and heterozygous (AQP0+/ΔC) lenses were imaged and analyzed at different developmental stages for transparency. Correspondingly, aberrations in the lens were characterized using the standard metal grid focusing method. Data were compared with age-matched WT, AQP0 knockout (AQP0-/-), and AQP0 heterozygous (AQP0+/-) lenses. Results AQP0ΔC/ΔC lenses were transparent throughout the embryonic development and until postnatal day 15 (P15) in contrast to age-matched AQP0-/- lenses, which developed cataract at embryonic stage itself. However, there was distortion aberration in AQP0ΔC/ΔC lens at P5; after P15, cataract began to develop and progressed faster surpassing that of age-matched AQP0-/- lenses. AQP0+/ΔC lenses were transparent even at the age of 1 year in contrast to AQP0+/- lenses; however, there was distortion aberration starting at P15. Conclusions A specific distribution profile of intact and end-cleaved AQP0 from the outer cortex to the inner nucleus is required in the lens for establishing refractive index gradient to enable proper focusing without aberrations and for maintaining transparency.
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Affiliation(s)
- Kulandaiappan Varadaraj
- Department of Physiology and Biophysics, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York, United States
| | - Sindhu Kumari
- Department of Physiology and Biophysics, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York, United States
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Kumari SS, Varadaraj K. A predominant form of C-terminally end-cleaved AQP0 functions as an open water channel and an adhesion protein in AQP0 ΔC/ΔC mouse lens. Biochem Biophys Res Commun 2019; 511:626-630. [PMID: 30826060 DOI: 10.1016/j.bbrc.2019.02.098] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2019] [Accepted: 02/19/2019] [Indexed: 01/14/2023]
Abstract
The purpose of this investigation was to find out whether C-terminally end-cleaved aquaporin 0 (AQP0), that is present predominantly in the lens mature fiber cells of the WT, functions as a water channel and a cell-to-cell adhesion (CTCA) protein in a knockin (KI) mouse model (AQP0ΔC/ΔC) that does not express intact AQP0. A genetically engineered KI mouse model, AQP0ΔC/ΔC, expressing only end-cleaved AQP0 was developed. This model expresses 1-246 amino acids of AQP0, instead of the full length 1-263 amino acids. Lens transparency of postnatal day 10 (P10) was analyzed qualitatively by dark field imaging. WT, AQP0+/- and AQP0+/ΔC lenses were transparent; AQP0-/- and AQP0ΔC/ΔC mouse lenses displayed loss of transparency. Lens fiber cell membrane vesicles (FCMVs) were prepared from wild type (WT), AQP0 heterozygous (AQP0+/-), AQP0 knockout (AQP0-/-), AQP0+/ΔC and AQP0ΔC/ΔC; water permeability (Pf) was measured using the osmotic shrinking method. CTCA assay was performed using adhesion-deficient L-cells and FCMVs prepared from the abovementioned genotypes. FCMVs of AQP0+/- and AQP0-/- showed a statistically significant reduction (P < 0.001) in Pf and CTCA compared to those of WT. AQP0+/ΔC and AQP0ΔC/ΔC FCMVs exhibited no statistically significant alteration (P > 0.05) in Pf compared to those of WT. However, CTCA of AQP0+/ΔC AQP0ΔC/ΔC FCMVs was significantly higher (P < 0.001) than that of WT FCMVs. Our experiments clearly show that C-terminally end-cleaved AQP0 can function both as a water channel and a CTCA molecule in the lens fiber cell membranes. Also, end-truncation plays an important role in increasing the CTCA between fiber cells.
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Affiliation(s)
| | - Kulandaiappan Varadaraj
- Physiology and Biophysics, Stony Brook University, NY, USA; SUNY Eye Institute, Syracuse, NY, USA.
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10
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Tapodi A, Clemens DM, Uwineza A, Jarrin M, Goldberg MW, Thinon E, Heal WP, Tate EW, Nemeth-Cahalan K, Vorontsova I, Hall JE, Quinlan RA. BFSP1 C-terminal domains released by post-translational processing events can alter significantly the calcium regulation of AQP0 water permeability. Exp Eye Res 2019; 185:107585. [PMID: 30790544 PMCID: PMC6713518 DOI: 10.1016/j.exer.2019.02.001] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2018] [Revised: 01/26/2019] [Accepted: 02/03/2019] [Indexed: 01/20/2023]
Abstract
BFSP1 (beaded filament structural protein 1, filensin) is a cytoskeletal protein expressed in the eye lens. It binds AQP0 in vitro and its C-terminal sequences have been suggested to regulate the water channel activity of AQP0. A myristoylated fragment from the C-terminus of BFSP1 was found in AQP0 enriched fractions. Here we identify BFSP1 as a substrate for caspase-mediated cleavage at several C-terminal sites including D433. Cleavage at D433 exposes a cryptic myristoylation sequence (434–440). We confirm that this sequence is an excellent substrate for both NMT1 and 2 (N-myristoyl transferase). Thus caspase cleavage may promote formation of myristoylated fragments derived from the BFSP1 C-terminus (G434-S665). Myristoylation at G434 is not required for membrane association. Biochemical fractionation and immunogold labeling confirmed that C-terminal BFSP1 fragments containing the myristoylation sequence colocalized with AQP0 in the same plasma membrane compartments of lens fibre cells. To determine the functional significance of the association of BFSP1 G434-S665 sequences with AQP0, we measured AQP0 water permeability in Xenopus oocytes co-transfected with transcripts expressing both AQP0 and various C-terminal domain fragments of BFSP1 generated by caspase cleavage. We found that different fragments dramatically alter the response of AQP0 to different concentrations of Ca2+. The complete C-terminal fragment (G434-S665) eliminates calcium regulation altogether. Shorter fragments can enhance regulation by elevated calcium or reverse the response, indicative of the regulatory potential of BFSP1 with respect to AQP0. In particular, elimination of the myristoylation site by the mutation G434A reverses the order of water permeability sensitivity to different Ca2+ concentrations.
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Affiliation(s)
- Antal Tapodi
- Department of Biosciences, The University of Durham, South Road, Durham, DH1 3LE, UK
| | | | - Alice Uwineza
- Department of Biosciences, The University of Durham, South Road, Durham, DH1 3LE, UK
| | - Miguel Jarrin
- Department of Biosciences, The University of Durham, South Road, Durham, DH1 3LE, UK
| | - Martin W Goldberg
- Department of Biosciences, The University of Durham, South Road, Durham, DH1 3LE, UK
| | - Emmanuelle Thinon
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, Wood Lane, London, W12 0BZ, UK; Institute of Chemical Biology, Molecular Sciences Research Hub, Imperial College London, Wood Lane, London, W12 0BZ, UK
| | - William P Heal
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, Wood Lane, London, W12 0BZ, UK; Institute of Chemical Biology, Molecular Sciences Research Hub, Imperial College London, Wood Lane, London, W12 0BZ, UK
| | - Edward W Tate
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, Wood Lane, London, W12 0BZ, UK; Institute of Chemical Biology, Molecular Sciences Research Hub, Imperial College London, Wood Lane, London, W12 0BZ, UK
| | | | | | - James E Hall
- Physiology and Biophysics, UC Irvine, Irvine, CA, USA.
| | - Roy A Quinlan
- Department of Biosciences, The University of Durham, South Road, Durham, DH1 3LE, UK; Biophysical Sciences Institute, The University of Durham, South Road, Durham, DH1 3LE, UK.
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11
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Friedrich MG, Wang Z, Schey KL, Truscott RJW. DehydroalanylGly, a new post translational modification resulting from the breakdown of glutathione. Biochim Biophys Acta Gen Subj 2018; 1862:907-913. [PMID: 29309825 DOI: 10.1016/j.bbagen.2018.01.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2017] [Revised: 12/05/2017] [Accepted: 01/05/2018] [Indexed: 12/28/2022]
Abstract
BACKGROUND The human body contains numerous long-lived proteins which deteriorate with age, typically by racemisation, deamidation, crosslinking and truncation. Previously we elucidated one reaction responsible for age-related crosslinking, the spontaneous formation of dehydroalanine (DHA) intermediates from phosphoserine and cysteine. This resulted in non-disulphide covalent crosslinks. The current paper outlines a novel posttranslational modification (PTM) in human proteins, which involves the addition of dehydroalanylglycine (DHAGly) to Lys residues. METHODS Human lens digests were examined by mass spectrometry for the presence of (DHA)Gly (+144.0535 Da) adducts to Lys residues. Peptide model studies were undertaken to elucidate the mechanism of formation. RESULTS In the lens, this PTM was detected at 18 lysine sites in 7 proteins. Using model peptides, a pathway for its formation was found to involve initial formation of the glutathione degradation product, γ-Glu(DHA)Gly from oxidised glutathione (GSSG). Once the Lys adduct formed, the Glu residue was lost in a hydrolytic mechanism apparently catalysed by the ε-amino group of the Lys. CONCLUSIONS This discovery suggests that within cells, the functional groups of amino acids in proteins may be susceptible to modification by reactive metabolites derived from GSSG. GENERAL SIGNIFICANCE Our finding demonstrates a novel +144.0535 Da PTM arising from the breakdown of oxidised glutathione.
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Affiliation(s)
- Michael G Friedrich
- Illawarra Health and Medical Research Institute, University of Wollongong, Wollongong, NSW 2500, Australia.
| | - Zhen Wang
- Department of Biochemistry and Mass Spectrometry Research Center, Vanderbilt University School of Medicine, Nashville, TN, USA
| | - Kevin L Schey
- Department of Biochemistry and Mass Spectrometry Research Center, Vanderbilt University School of Medicine, Nashville, TN, USA
| | - Roger J W Truscott
- Illawarra Health and Medical Research Institute, University of Wollongong, Wollongong, NSW 2500, Australia
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Wang Z, Schey KL. Identification of a direct Aquaporin-0 binding site in the lens-specific cytoskeletal protein filensin. Exp Eye Res 2017; 159:23-29. [PMID: 28259670 DOI: 10.1016/j.exer.2017.02.012] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2016] [Revised: 02/14/2017] [Accepted: 02/15/2017] [Indexed: 10/20/2022]
Abstract
An interaction between the C-terminus of aquaporin-0 (AQP0) and lens beaded filament protein filensin has been reported previously; however, the region of filensin that is involved in the interaction has not been determined. This study is designed to identify the region of filensin that interacts with AQP0. Chemical crosslinking coupled with mass spectrometry was used to identify the site of interaction. The protein complex was crosslinked with zero-length crosslinker: 1-Ethyl-3-[3-dimethylaminopropyl]carbodiimide Hydrochloride (EDC). The crosslinked membrane fraction was digested by trypsin and crosslinked peptides were identified by liquid chromatography-tandem mass spectrometry. A crosslinked peptide between bovine filensin 450-465 (VKGPKEPEPPADLYTK) and bovine AQP0 239-259 (GSRPSESNGQPEVTGEPVELK) was detected. AQP0/filensin crosslinking was not detected in superficial young fiber cells, but increased with fiber cell age in the lens cortex. AQP0/filensin crosslinking and filensin truncation were observed in the same regions of the lens. This crosslinked peptide can be detected in 75 kDa gel band confirming that AQP0/filensin crosslinking can occur between AQP0 and the filensin C-terminal fragment. These results suggest that the AQP0 C-terminus directly interacts with the region of filensin that is adjacent to the major truncation site and the polybasic cluster of residues in the filensin C-terminal tail. This interaction occurs in a specific region of the lens and could only occur between AQP0 and filensin C-terminal fragment in vivo. This interaction supports the dual roles of filensin in the lens; roles that could be important during lens development.
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Affiliation(s)
- Zhen Wang
- Department of Biochemistry, Vanderbilt University, Nashville, TN 37232, USA
| | - Kevin L Schey
- Department of Biochemistry, Vanderbilt University, Nashville, TN 37232, USA.
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Slavi N, Wang Z, Harvey L, Schey KL, Srinivas M. Identification and Functional Assessment of Age-Dependent Truncations to Cx46 and Cx50 in the Human Lens. Invest Ophthalmol Vis Sci 2016; 57:5714-5722. [PMID: 27787559 PMCID: PMC5089213 DOI: 10.1167/iovs.16-19698] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2016] [Accepted: 08/21/2016] [Indexed: 11/24/2022] Open
Abstract
PURPOSE Many proteins in the lens undergo extensive posttranslational modifications (PTMs) with age, leading to alterations in their function. The extent to which lens gap junction proteins, Cx46 and Cx50, accumulate PTMs with aging is not known. In this study, we identified truncations in Cx46 and Cx50 in the human lens using mass spectrometry. We also examined the effect of truncations on channel function using electrophysiological measurements. METHODS Human lenses were dissected into cortex, outer nucleus, and nucleus regions, and fiber cell membranes were subjected to trypsin digestion. Tryptic peptides were analyzed by liquid chromatography (LC)-electrospray tandem mass spectrometry (ESI/MS/MS). Effects of truncations on channel conductance, permeability, and gating were assessed in transfected cells. RESULTS Cleavage sites were identified in the C-terminus, the cytoplasmic loop, and the N-terminus of Cx46 and Cx50. Levels of C-terminal truncations, which were found at residues 238 to 251 in Cx46 and at residues 238 to 253 and 274 to 284 in Cx50, were similar in different lens regions. In contrast, levels of truncations in cytoplasmic loop and N-terminal domains of Cx46 and Cx50 increased dramatically from outer cortex to nucleus. Most of the C-terminally truncated proteins were functional, whereas truncations in the cytoplasmic loop did not result in the formation of functional channels. CONCLUSIONS Accumulation of cytoplasmic loop and N-terminal truncations in the core might lead to decreases in coupling with age. This reduction is expected to lead to an increase in intracellular calcium and a decrease in levels of glutathione in the nucleus. These changes may ultimately lead to age-related nuclear cataracts.
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Affiliation(s)
- Nefeli Slavi
- Department of Biological and Vision Sciences and the Graduate Center for Vision Research, SUNY College of Optometry, New York, New York, United States
| | - Zhen Wang
- Department of Biochemistry and Mass Spectrometry Research Center Vanderbilt University School of Medicine, Nashville, Tennessee, United States
| | - Lucas Harvey
- Department of Biological and Vision Sciences and the Graduate Center for Vision Research, SUNY College of Optometry, New York, New York, United States
| | - Kevin L. Schey
- Department of Biochemistry and Mass Spectrometry Research Center Vanderbilt University School of Medicine, Nashville, Tennessee, United States
| | - Miduturu Srinivas
- Department of Biological and Vision Sciences and the Graduate Center for Vision Research, SUNY College of Optometry, New York, New York, United States
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Wenke JL, McDonald WH, Schey KL. Spatially Directed Proteomics of the Human Lens Outer Cortex Reveals an Intermediate Filament Switch Associated With the Remodeling Zone. Invest Ophthalmol Vis Sci 2016; 57:4108-14. [PMID: 27537260 PMCID: PMC4991037 DOI: 10.1167/iovs.16-19791] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2016] [Accepted: 06/15/2016] [Indexed: 01/25/2023] Open
Abstract
PURPOSE To quantify protein changes in the morphologically distinct remodeling zone (RZ) and adjacent regions of the human lens outer cortex using spatially directed quantitative proteomics. METHODS Lightly fixed human lens sections were deparaffinized and membranes labeled with fluorescent wheat germ agglutinin (WGA-TRITC). Morphology directed laser capture microdissection (LCM) was used to isolate tissue from four distinct regions of human lens outer cortex: differentiating zone (DF), RZ, transition zone (TZ), and inner cortex (IC). Liquid chromatography-tandem mass spectrometry (LC-MS/MS) of the plasma membrane fraction from three lenses (21-, 22-, and 27-year) revealed changes in major cytoskeletal proteins including vimentin, filensin, and phakinin. Peptides from proteins of interest were quantified using multiple reaction monitoring (MRM) mass spectrometry and isotopically-labeled internal peptide standards. RESULTS Results revealed an intermediate filament switch from vimentin to beaded filament proteins filensin and phakinin that occurred at the RZ. Several other cytoskeletal proteins showed significant changes between regions, while most crystallins remained unchanged. Targeted proteomics provided accurate, absolute quantification of these proteins and confirmed vimentin, periplakin, and periaxin decrease from the DF to the IC, while filensin, phakinin, and brain acid soluble protein 1 (BASP1) increase significantly at the RZ. CONCLUSIONS Mass spectrometry-compatible fixation and morphology directed laser capture enabled proteomic analysis of narrow regions in the human lens outer cortex. Results reveal dramatic cytoskeletal protein changes associated with the RZ, suggesting that one role of these proteins is in membrane deformation and/or the establishment of ball and socket joints in the human RZ.
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15
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Intact and N- or C-terminal end truncated AQP0 function as open water channels and cell-to-cell adhesion proteins: end truncation could be a prelude for adjusting the refractive index of the lens to prevent spherical aberration. Biochim Biophys Acta Gen Subj 2014; 1840:2862-77. [PMID: 24821012 DOI: 10.1016/j.bbagen.2014.05.002] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2013] [Revised: 04/30/2014] [Accepted: 05/02/2014] [Indexed: 11/20/2022]
Abstract
BACKGROUND Investigate the impact of natural N- or C-terminal post-translational truncations of lens mature fiber cell Aquaporin 0 (AQP0) on water permeability (Pw) and cell-to-cell adhesion (CTCA) functions. METHODS The following deletions/truncations were created by site-directed mutagenesis (designations in parentheses): Amino acid residues (AA) 2-6 (AQP0-N-del-2-6), AA235-263 (AQP0-1-234), AA239-263 (AQP0-1-238), AA244-263 (AQP0-1-243), AA247-263 (AQP0-1-246), AA250-263 (AQP0-1-249) and AA260-263 (AQP0-1-259). Protein expression was studied using immunostaining, fluorescent tags and organelle-specific markers. Pw was tested by expressing the respective complementary ribonucleic acid (cRNA) in Xenopus oocytes and conducting osmotic swelling assay. CTCA was assessed by transfecting intact or mutant AQP0 into adhesion-deficient L-cells and performing cell aggregation and adhesion assays. RESULTS AQP0-1-234 and AQP0-1-238 did not traffic to the plasma membrane. Trafficking of AQP0-N-del-2-6 and AQP0-1-243 was reduced causing decreased membrane Pw and CTCA. AQP0-1-246, AQP0-1-249 and AQP0-1-259 mutants trafficked properly and functioned normally. Pw and CTCA functions of the mutants were directly proportional to the respective amount of AQP0 expressed at the plasma membrane and remained comparable to those of intact AQP0 (AQP0-1-263). CONCLUSIONS Post-translational truncation of N- or C-terminal end amino acids does not alter the basal water permeability of AQP0 or its adhesive functions. AQP0 may play a role in adjusting the refractive index to prevent spherical aberration in the constantly growing lens. GENERAL SIGNIFICANCE Similar studies can be extended to other lens proteins which undergo post-translational truncations to find out how they assist the lens to maintain transparency and homeostasis for proper focusing of objects on to the retina.
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16
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Wang Z, Lyons B, Truscott RJW, Schey KL. Human protein aging: modification and crosslinking through dehydroalanine and dehydrobutyrine intermediates. Aging Cell 2014; 13:226-34. [PMID: 24134651 PMCID: PMC4114717 DOI: 10.1111/acel.12164] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/12/2013] [Indexed: 11/29/2022] Open
Abstract
Nonenzymatic post-translational modification (PTM) of proteins is a fundamental molecular process of aging. The combination of various modifications and their accumulation with age not only affects function, but leads to crosslinking and protein aggregation. In this study, aged human lens proteins were examined using HPLC–tandem mass spectrometry and a blind PTM search strategy. Multiple thioether modifications of Ser and Thr residues by glutathione (GSH) and its metabolites were unambiguously identified. Thirty-four of 36 sites identified on 15 proteins were found on known phosphorylation sites, supporting a mechanism involving dehydroalanine (DHA) and dehydrobutyrine (DHB) formation through β-elimination of phosphoric acid from phosphoserine and phosphothreonine with subsequent nucleophilic attack by GSH. In vitro incubations of phosphopeptides demonstrated that this process can occur spontaneously under physiological conditions. Evidence that this mechanism can also lead to protein–protein crosslinks within cells is provided where five crosslinked peptides were detected in a human cataractous lens. Nondisulfide crosslinks were identified for the first time in lens tissue between βB2- & βB2-, βA4- & βA3-, γS- & βB1-, and βA4- & βA4-crystallins and provide detailed structural information on in vivo crystallin complexes. These data suggest that phosphoserine and phosphothreonine residues represent susceptible sites for spontaneous breakdown in long-lived proteins and that DHA- and DHB-mediated protein crosslinking may be the source of the long-sought after nondisulfide protein aggregates believed to scatter light in cataractous lenses. Furthermore, this mechanism may be a common aging process that occurs in long-lived proteins of other tissues leading to protein aggregation diseases.
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Affiliation(s)
- Zhen Wang
- Department of Biochemistry and Mass Spectrometry Research Center Vanderbilt University School of Medicine Nashville TN 37232 USA
| | - Brian Lyons
- Save Sight Institute University of Sydney Sydney NSW 2000 Australia
| | - Roger J. W. Truscott
- Illawarra Health and Medical Research Institute University of Wollongong Wollongong NSW 2522 Australia
| | - Kevin L. Schey
- Department of Biochemistry and Mass Spectrometry Research Center Vanderbilt University School of Medicine Nashville TN 37232 USA
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17
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Lampi KJ, Wilmarth PA, Murray MR, David LL. Lens β-crystallins: the role of deamidation and related modifications in aging and cataract. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2014; 115:21-31. [PMID: 24613629 DOI: 10.1016/j.pbiomolbio.2014.02.004] [Citation(s) in RCA: 99] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/02/2014] [Revised: 02/12/2014] [Accepted: 02/14/2014] [Indexed: 11/26/2022]
Abstract
Crystallins are the major proteins in the lens of the eye and function to maintain transparency of the lens. Of the human crystallins, α, β, and γ, the β-crystallins remain the most elusive in their structural significance due to their greater number of subunits and possible oligomer formations. The β-crystallins are also heavily modified during aging. This review focuses on the functional significance of deamidation and the related modifications of racemization and isomerization, the major modifications in β-crystallins of the aged human lens. Elucidating the role of these modifications in cataract formation has been slow, because they are analytically among the most difficult post-translational modifications to study. Recent results suggest that many amides deamidate to similar extent in normal aged and cataractous lenses, while others may undergo greater deamidation in cataract. Mimicking deamidation at critical structural regions induces structural changes that disrupt the stability of the β-crystallins and lead to their aggregation in vitro. Deamidations at the surface disrupt interactions with other crystallins. Additionally, the α-crystallin chaperone is unable to completely prevent deamidated β-crystallins from insolubilization. Therefore, deamidation of β-crystallins may enhance their precipitation and light scattering in vivo contributing to cataract formation. Future experiments are needed to quantify differences in deamidation rates at all Asn and Gln residues within crystallins from aged and cataractous lenses, as well as racemization and isomerization which potentially perturb protein structure greater than deamidation alone. Quantitative data is greatly needed to investigate the importance of these major age-related modifications in cataract formation.
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Affiliation(s)
- Kirsten J Lampi
- Oregon Health & Science University, Integrative Biosciences, 611 SW Campus Drive, Portland, OR 97239, USA.
| | - Phillip A Wilmarth
- Oregon Health & Science University, Biochemistry and Molecular Biology, 3181 Sam Jackson Park Road, Portland, OR 97239-3098, USA
| | - Matthew R Murray
- Oregon Health & Science University, Integrative Biosciences, 611 SW Campus Drive, Portland, OR 97239, USA
| | - Larry L David
- Oregon Health & Science University, Biochemistry and Molecular Biology, 3181 Sam Jackson Park Road, Portland, OR 97239-3098, USA
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Wang Z, Han J, David LL, Schey KL. Proteomics and phosphoproteomics analysis of human lens fiber cell membranes. Invest Ophthalmol Vis Sci 2013; 54:1135-43. [PMID: 23349431 DOI: 10.1167/iovs.12-11168] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
PURPOSE The human lens fiber cell insoluble membrane fraction contains important membrane proteins, cytoskeletal proteins, and cytosolic proteins that are strongly associated with the membrane. The purpose of this study was to characterize the lens fiber cell membrane proteome and phosphoproteome from human lenses. METHODS HPLC-mass spectrometry-based multidimensional protein identification technology (MudPIT), without or with phosphopeptide enrichment, was applied to study the proteome and phosphoproteome of lens fiber cell membranes, respectively. RESULTS In total, 951 proteins were identified, including 379 integral membrane and membrane-associated proteins. Enriched gene categories and pathways based on the proteomic analysis include carbohydrate metabolism (glycolysis/gluconeogenesis, pentose phosphate pathway, pyruvate metabolism), proteasome, cell-cell signaling and communication (GTP binding, gap junction, focal adhesion), glutathione metabolism, and actin regulation. The combination of TiO(2) phosphopeptide enrichment and MudPIT analysis revealed 855 phosphorylation sites on 271 proteins, including 455 phosphorylation sites that have not been previously identified. PKA, PKC, CKII, p38MAPK, and RSK are predicted as the major kinases for phosphorylation on the sites identified in the human lens membrane fraction. CONCLUSIONS The results presented herein significantly expand the characterized proteome and phosphoproteome of the human lens fiber cell and provide a valuable reference for future research in studies of lens development and disease.
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Affiliation(s)
- Zhen Wang
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN, USA
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19
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Abstract
A newcomer to the -omics era, proteomics, is a broad instrument-intensive research area that has advanced rapidly since its inception less than 20 years ago. Although the 'wet-bench' aspects of proteomics have undergone a renaissance with the improvement in protein and peptide separation techniques, including various improvements in two-dimensional gel electrophoresis and gel-free or off-gel protein focusing, it has been the seminal advances in MS that have led to the ascension of this field. Recent improvements in sensitivity, mass accuracy and fragmentation have led to achievements previously only dreamed of, including whole-proteome identification, and quantification and extensive mapping of specific PTMs (post-translational modifications). With such capabilities at present, one might conclude that proteomics has already reached its zenith; however, 'capability' indicates that the envisioned goals have not yet been achieved. In the present review we focus on what we perceive as the areas requiring more attention to achieve the improvements in workflow and instrumentation that will bridge the gap between capability and achievement for at least most proteomes and PTMs. Additionally, it is essential that we extend our ability to understand protein structures, interactions and localizations. Towards these ends, we briefly focus on selected methods and research areas where we anticipate the next wave of proteomic advances.
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Costello MJ, Burette A, Weber M, Metlapally S, Gilliland KO, Fowler WC, Mohamed A, Johnsen S. Electron tomography of fiber cell cytoplasm and dense cores of multilamellar bodies from human age-related nuclear cataracts. Exp Eye Res 2012; 101:72-81. [PMID: 22728317 DOI: 10.1016/j.exer.2012.06.005] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2012] [Revised: 06/09/2012] [Accepted: 06/11/2012] [Indexed: 01/29/2023]
Abstract
Human nuclear cataract formation is a multi-factorial disease with contributions to light scattering from many cellular sources that change their scattering properties over decades. The aging process produces aggregation of cytoplasmic crystallin proteins, which alters the protein packing and texture of the cytoplasm. Previous studies of the cytoplasmic texture quantified increases in density fluctuations in protein packing and theoretically predicted the corresponding scattering. Multilamellar bodies (MLBs) are large particles with a core of crystallin cytoplasm that have been suggested to be major sources of scattering in human nuclei. The core has been shown to condense over time such that the refractive index increases compared to the adjacent aged and textured cytoplasm. Electron tomography is used here to visualize the 3D arrangement of protein aggregates in aged and cataractous lens nuclear cytoplasm compared to the dense protein packing in the cores of MLBs. Thin sections, 70 nm thick, were prepared from epoxy-embedded human transparent donor lenses and nuclear cataracts. Tilt series were collected on an FEI T20 transmission electron microscope (TEM) operated at 200 kV using 15 nm gold particles as fiducial markers. Images were aligned and corrected with FEI software and reconstructed with IMOD and other software packages to produce animated tilt series and stereo anaglyphs. The 3D views of protein density showed the relatively uniform packing of proteins in aged transparent lens nuclear cytoplasm and less dense packing of aged cataractous cytoplasm where many low-density regions can be appreciated in the absence of the TEM projection artifacts. In contrast the cores of the MLBs showed a dense packing of protein with minimal density fluctuations. These observations support the conclusion that, during the nuclear cataract formation, alterations in protein packing are extensive and can result in pronounced density fluctuations. Aging causes the MLB cores to become increasingly different in their protein packing from the adjacent cytoplasm. These results support the hypothesis that the MLBs increase their scattering with age and nuclear cataract formation.
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Affiliation(s)
- M Joseph Costello
- Department of Cell and Developmental Biology, CB 7090, University of North Carolina, Chapel Hill, NC 27599, USA.
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21
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Nakazawa Y, Oka M, Furuki K, Mitsuishi A, Nakashima E, Takehana M. The effect of the interaction between aquaporin 0 (AQP0) and the filensin tail region on AQP0 water permeability. Mol Vis 2011; 17:3191-9. [PMID: 22194645 PMCID: PMC3244488] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2011] [Accepted: 12/06/2011] [Indexed: 10/27/2022] Open
Abstract
PURPOSE To study the interaction between the lens-specific water channel protein, aquaporin 0 (AQP0) and the lens-specific intermediate filament protein, filensin, and the effect of this interaction on the water permeability of AQP0. The effect of other factors on the interaction was also investigated. METHODS Expression plasmids were constructed in which glutathione-S-transferase (GST) was fused to the AQP0 COOH-terminal region (GST-AQP0-C), which contains the major phosphorylation sites of the protein. Plasmids for AQP0 COOH-terminal mutants were also constructed in which one, three or five sites were pseudophosphorylated, and the proteins expressed from these GST-fusion plasmids were assayed for their interaction with lens proteins. Expressed recombinant GST-fusion proteins were purified using glutathione beads and incubated with rat lens extract. Western blotting was used to identify the lens proteins that interacted with the GST-fusion proteins. Filensin tail and rod domains were also expressed as GST-fusion proteins and their interactions with AQPO were analyzed. Additionally, the water permeability of AQP0 was calculated by expressing AQP0 with or without the filensin peptide on the cell membrane of Xenopus oocytes by injecting cRNAs for AQP0 and filensin. RESULTS The GST-AQP0-C construct interacted with the tail region of lens filensin and the GST-filensin-tail construct interacted with lens AQP0, but the GST-filensin-rod construct did not interact with AQP0. GST-AQP0-C also interacted with a purified recombinant filensin-tail peptide after cleavage from GST. The AQP0/filensin-tail interaction was not affected by pseudophosphorylation of the AQP0 COOH-terminal tail, nor was it affected by changes in pH. Xenopus oocytes expressing AQP0 on the plasma membrane showed increased water permeability, which was lowered when the filensin COOH-terminal peptide cRNA was coinjected with the cRNA for AQP0. CONCLUSIONS The filensin COOH-terminal tail region interacted with the AQP0 COOH-terminal region and the results strongly suggested that the interaction was direct. It appears that interactions between AQP0 and filensin helps to regulate the water permeability of AQP0 and to organize the structure of lens fiber cells, and may also help to maintain the transparency of the lens.
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Affiliation(s)
- Yosuke Nakazawa
- Department of Molecular Function and Physiology, Faculty of Pharmacy, Keio University, Tokyo, Japan
| | - Mikako Oka
- Department of Molecular Function and Physiology, Faculty of Pharmacy, Keio University, Tokyo, Japan
| | - Katsuya Furuki
- Department of Molecular Function and Physiology, Faculty of Pharmacy, Keio University, Tokyo, Japan
| | - Akiko Mitsuishi
- Department of Molecular Function and Physiology, Faculty of Pharmacy, Keio University, Tokyo, Japan
| | - Emi Nakashima
- Department of Parmaceutics, Faculty of Pharmacy, Keio University, Tokyo, Japan
| | - Makoto Takehana
- Department of Molecular Function and Physiology, Faculty of Pharmacy, Keio University, Tokyo, Japan
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Wang Z, Schey KL. Aquaporin-0 interacts with the FERM domain of ezrin/radixin/moesin proteins in the ocular lens. Invest Ophthalmol Vis Sci 2011; 52:5079-87. [PMID: 21642618 DOI: 10.1167/iovs.10-6998] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
PURPOSE Aquaporin 0 (AQP0) is the major intrinsic protein in the lens and is essential for establishing proper fiber cell structure and organization. Cytoskeletal proteins that directly interact with the C terminus of AQP0 are identified herein. METHODS The water-insoluble fraction of lens fiber cells was chemically cross-linked, and cross-linked peptides with the C terminus of AQP0 were identified by mass spectrometry. Coimmunoprecipitation and AQP0 C-terminal peptide pulldown experiments were used to confirm the protein-protein interaction. RESULTS Unexpectedly, AQP0 was found to directly associate with ezrin/radixin/moesin (ERM) family members, proteins that are involved in linkage of actin filaments to the plasma membrane. Cross-linked peptides were detected between AQP0 and degenerate sequences of ezrin and radixin; however, AQP0 interaction with ezrin is believed to play a more significant function in the lens because of its higher level of expression and observed ezrin-specific cross-linking. The interaction was found to occur between the C terminus of AQP0 and subdomains F1 and F3 of ERM proteins. The interaction between AQP0 and ezrin was confirmed by coimmunoprecipitation and AQP0 C-terminal peptide pulldown experiments. CONCLUSIONS Considering the important known functions of the cellular actin cytoskeleton in fiber cell differentiation, the interaction of AQP0 and ERM proteins may play an important role in fiber cell morphology, elongation, and organization.
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Affiliation(s)
- Zhen Wang
- Mass Spectrometry Research Center and Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-8575, USA
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Su SP, McArthur JD, Truscott RJW, Aquilina JA. Truncation, cross-linking and interaction of crystallins and intermediate filament proteins in the aging human lens. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2011; 1814:647-56. [PMID: 21447408 DOI: 10.1016/j.bbapap.2011.03.014] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2010] [Revised: 02/14/2011] [Accepted: 03/22/2011] [Indexed: 11/30/2022]
Abstract
The optical properties of the lens are dependent upon the integrity of proteins within the fiber cells. During aging, crystallins, the major intra-cellular structural proteins of the lens, aggregate and become water-insoluble. Modifications to crystallins and the lens intermediate filaments have been implicated in this phenomenon. In this study, we examined changes to, and interactions between, human lens crystallins and intermediate filament proteins in lenses from a variety of age groups (0-86years). Among the lens-specific intermediate filament proteins, filensin was extensively cleaved in all postnatal lenses, with truncated products of various sizes being found in both the lens cortical and nuclear extracts. Phakinin was also truncated and was not detected in the lens nucleus. The third major intermediate filament protein, vimentin, remained intact in lens cortical fiber cells across the age range except for an 86year lens, where a single ~49kDa breakdown product was observed. An αB-crystallin fusion protein (maltose-binding protein-αB-crystallin) was found to readily exchange subunits with endogenous α-crystallin, and following mild heat stress, to bind to filensin, phakinin and vimentin and to several of their truncated products. Tryptic digestion of a truncated form of filensin suggested that the binding site for α-crystallin may be in the N-terminal region. The presence of significant amounts of small peptides derived from γS- and βB1-crystallins in the water-insoluble fraction of the lens indicates that these interact tightly with cytoskeletal or membrane components. Interestingly, water-soluble complexes (~40kDa) contained predominantly γS- and βB1-crystallins, suggesting that cross-linking is an alternative pathway for modified β- and γ-crystallins in the lens.
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Affiliation(s)
- Shih-Ping Su
- School of Biological Sciences, University of Wollongong, Wollongong, NSW 2522, Australia.
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24
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Huang CH, Wang YT, Tsai CF, Chen YJ, Lee JS, Chiou SH. Phosphoproteomics characterization of novel phosphorylated sites of lens proteins from normal and cataractous human eye lenses. Mol Vis 2011; 17:186-98. [PMID: 21264232 PMCID: PMC3025096] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2010] [Accepted: 01/14/2011] [Indexed: 12/01/2022] Open
Abstract
PURPOSE Post-translational modification (PTM) of lens proteins is believed to play various roles in age-related lens function and development. Among the different types of PTM, phosphorylation is most noteworthy to play a major role in the regulation of various biosignaling pathways in relation to metabolic processes and cellular functions. The present study reported the quantitative analysis of the in vivo phosphoproteomics profiles of human normal and cataractous lenses with the aim of identifying specific phosphorylation sites which may provide insights into the physiologic significance of phosphorylation in relation to cataract formation. METHODS To improve detection sensitivity of low abundant proteins, we first adopted SDS-gel electrophoresis fractionation of lens extracts to identify and compare the protein compositions between normal and cataractous lenses, followed by tryptic digestion, enrichment of phosphopeptides by immobilized metal affinity chromatography (IMAC) and nano-liquid chromatography coupled tandem mass spectrometry (nanoLC-MS/MS) analysis. RESULTS By comprehensively screening of the phosphoproteome in normal and cataractous lenses, we identified 32 phosphoproteins and 73 phosphorylated sites. The most abundantly phosphorylated proteins are two subunits of β-crystallin, i.e., βB1-crystallin (12%) and βB2-crystallin (12%). Moreover, serine was found to be the most abundantly phosphorylated residue (72%) in comparison with threonine (24%) and tyrosine (4%) in the lens phosphoproteome. The quantitative analysis revealed significant and distinct changes of 19 phosphoproteins corresponding to 28 phosphorylated sites between these two types of human lenses, including 20 newly discovered novel phosphorylation sites on lens proteins. CONCLUSIONS The shotgun phosphoproteomics approach to characterize protein phosphorylation may be adapted and extended to the comprehensive analysis of other types of post-translational modification of lens proteins in vivo. The identification of these novel phosphorylation sites in lens proteins that showed differential expression in the cataractous lens may bear some unknown physiologic significance and provide insights into phosphorylation-related human eye diseases, which warrant further investigation in the future.
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Affiliation(s)
- Chun-Hao Huang
- Graduate Institute of Medicine and Center for Research Resources and Development, Kaohsiung Medical University, Kaohsiung, Taiwan,Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan
| | - Yi-Ting Wang
- Institute of Chemistry, Academia Sinica, Taipei, Taiwan,Chemical Biology and Molecular Biophysics Program, Taiwan International Graduate Program, Institute of Chemistry, Academia Sinica, Taipei, Taiwan,Institute of Biochemical Sciences, National Taiwan University, Taipei, Taiwan
| | - Chia-Feng Tsai
- Institute of Chemistry, Academia Sinica, Taipei, Taiwan,Department of Chemistry, National Taiwan University, Taipei, Taiwan
| | - Yu-Ju Chen
- Institute of Chemistry, Academia Sinica, Taipei, Taiwan,Institute of Biochemical Sciences, National Taiwan University, Taipei, Taiwan,Department of Chemistry, National Taiwan University, Taipei, Taiwan
| | - Jiahn-Shing Lee
- Department of Ophthalmology, Chang-Gung Memorial Hospital, Chang-Gung University, Taipei, Taiwan
| | - Shyh-Horng Chiou
- Graduate Institute of Medicine and Center for Research Resources and Development, Kaohsiung Medical University, Kaohsiung, Taiwan,Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan
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