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Structural basis for lamin assembly at the molecular level. Nat Commun 2019; 10:3757. [PMID: 31434876 PMCID: PMC6704074 DOI: 10.1038/s41467-019-11684-x] [Citation(s) in RCA: 64] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2019] [Accepted: 07/26/2019] [Indexed: 12/02/2022] Open
Abstract
Nuclear structure and function are governed by lamins, which are intermediate filaments that mostly consist of α-helices. Different lamin assembly models have been proposed based on low resolution and fragmented structures. However, their assembly mechanisms are still poorly understood at the molecular level. Here, we present the crystal structure of a long human lamin fragment at 3.2 Å resolution that allows the visualization of the features of the full-length protein. The structure shows an anti-parallel arrangement of the two coiled-coil dimers, which is important for the assembly process. We further discover an interaction between the lamin dimers by using chemical cross-linking and mass spectrometry analysis. Based on these two interactions, we propose a molecular mechanism for lamin assembly that is in agreement with a recent model representing the native state and could explain pathological mutations. Our findings also provide the molecular basis for assembly mechanisms of other intermediate filaments. Lamins are intermediate filaments and the major component of the nuclear lamina. Here the authors determine the crystal structure of a construct comprising the N-terminal half of human lamin A/C and use their structure and cross-linking and biochemical experiments to discuss lamin assembly.
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Jarrin M, Young L, Wu W, Girkin JM, Quinlan RA. In vivo, Ex Vivo, and In Vitro Approaches to Study Intermediate Filaments in the Eye Lens. Methods Enzymol 2016; 568:581-611. [DOI: 10.1016/bs.mie.2015.09.010] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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Qu B, Landsbury A, Schönthaler HB, Dahm R, Liu Y, Clark JI, Prescott AR, Quinlan RA. Evolution of the vertebrate beaded filament protein, Bfsp2; comparing the in vitro assembly properties of a "tailed" zebrafish Bfsp2 to its "tailless" human orthologue. Exp Eye Res 2011; 94:192-202. [PMID: 22182672 DOI: 10.1016/j.exer.2011.12.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2011] [Revised: 11/30/2011] [Accepted: 12/02/2011] [Indexed: 11/25/2022]
Abstract
In bony fishes, Bfsp2 orthologues are predicted to possess a C-terminal tail domain, which is absent from avian, amphibian and mammalian Bfsp2 sequences. These sequences, are however, not conserved between fish species and therefore questions whether they have a functional role. For other intermediate filament proteins, the C-terminal tail domain is important for both filament assembly and regulating interactions between filaments. We confirm that zebrafish has a single Bfsp2 gene by radiation mapping. Two transcripts (bfsp2α and bfsp2β) are produced by alternative splicing of the last exon. Using a polyclonal antibody specific to a tridecameric peptide in the C-terminal tail domain common to both zebrafish Bfsp2 splice variants, we have confirmed its expression in zebrafish lens fibre cells. We have also determined the in vitro assembly properties of zebrafish Bfsp2α and conclude that the C-terminal sequences are required to regulate not only the diameter and uniformity of the in vitro assembly filaments, but also their filament-filament associations in vitro. Therefore we conclude zebrafish Bfsp2α is a functional orthologue conforming more closely to the conventional domain structure of intermediate filament proteins. Data mining of the genome databases suggest that the loss of this tail domain could occur in several stages leading eventually to completely tailless orthologues, such as human BFSP2.
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Shi Q, Banks EA, Yu XS, Gu S, Lauer J, Fields GB, Jiang JX. Amino acid residue Val362 plays a critical role in maintaining the structure of C terminus of connexin 50 and in lens epithelial-fiber differentiation. J Biol Chem 2010; 285:18415-22. [PMID: 20395299 DOI: 10.1074/jbc.m110.107052] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have previously shown that connexin (Cx) 50, unlike the other two lens connexins, Cx43 and Cx46, promotes chicken lens epithelial-fiber differentiation in a channel-independent manner. Here, we show that deletion of the PEST motif at the C terminus (CT) domain of Cx50 attenuates the stimulatory effect of Cx50 on lens fiber differentiation. Valine 362, a residue located within the PEST domain, is functionally involved. The structure of the Cx50 CT predicted by molecular modeling revealed four alpha-helices and Val(362) was found to be located in the middle of the 3rd helix. Replacement of Val(362) with amino acid residues that disrupt the alpha-helical structure predicted by molecular modeling, such as arginine, glutamate, or phenylalanine, attenuated the stimulatory effects of Cx50 on lens differentiation, whereas replacement with threonine, isoleucine, leucine, or proline, which maintain the structure preserved the function of Cx50. Circular dichroism (CD) studies supported the structural predictions and showed that the substitution with Glu, but not Thr or Pro, disrupted the alpha-helix, which appears to be the structural feature important for lens epithelial-fiber differentiation. Together, our results suggest that Val(362) is important for maintaining the helical structure and is crucial for the role of Cx50 in promoting lens epithelial-fiber differentiation.
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Affiliation(s)
- Qian Shi
- Department of Biochemistry, University of Texas Health Science Center, San Antonio, Texas 78229-3900, USA
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Lens intermediate filaments. Exp Eye Res 2008; 88:165-72. [PMID: 19071112 DOI: 10.1016/j.exer.2008.11.007] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2008] [Revised: 11/04/2008] [Accepted: 11/04/2008] [Indexed: 12/12/2022]
Abstract
The ocular lens assembles two separate intermediate filament systems sequentially with differentiation. Canonical 8-11 nm IFs composed of Vimentin are assembled in lens epithelial cells and younger fiber cells, while the fiber cell-specific beaded filaments are switched on as fiber cell elongation initiates. Some of the key features of both filament systems are reviewed.
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Perng MD, Wen SF, Gibbon T, Middeldorp J, Sluijs J, Hol EM, Quinlan RA. Glial fibrillary acidic protein filaments can tolerate the incorporation of assembly-compromised GFAP-delta, but with consequences for filament organization and alphaB-crystallin association. Mol Biol Cell 2008; 19:4521-33. [PMID: 18685083 DOI: 10.1091/mbc.e08-03-0284] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The glial fibrillary acidic protein (GFAP) gene is alternatively spliced to give GFAP-alpha, the most abundant isoform, and seven other differentially expressed transcripts including GFAP-delta. GFAP-delta has an altered C-terminal domain that renders it incapable of self-assembly in vitro. When titrated with GFAP-alpha, assembly was restored providing GFAP-delta levels were kept low (approximately 10%). In a range of immortalized and transformed astrocyte derived cell lines and human spinal cord, we show that GFAP-delta is naturally part of the endogenous intermediate filaments, although levels were low (approximately 10%). This suggests that GFAP filaments can naturally accommodate a small proportion of assembly-compromised partners. Indeed, two other assembly-compromised GFAP constructs, namely enhanced green fluorescent protein (eGFP)-tagged GFAP and the Alexander disease-causing GFAP mutant, R416W GFAP both showed similar in vitro assembly characteristics to GFAP-delta and could also be incorporated into endogenous filament networks in transfected cells, providing expression levels were kept low. Another common feature was the increased association of alphaB-crystallin with the intermediate filament fraction of transfected cells. These studies suggest that the major physiological role of the assembly-compromised GFAP-delta splice variant is as a modulator of the GFAP filament surface, effecting changes in both protein- and filament-filament associations as well as Jnk phosphorylation.
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Affiliation(s)
- Ming-Der Perng
- School of Biological and Biomedical Sciences, The University of Durham, Durham DH1 3LE, United Kingdom
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Perng MD, Zhang Q, Quinlan RA. Insights into the beaded filament of the eye lens. Exp Cell Res 2007; 313:2180-8. [PMID: 17490642 PMCID: PMC5073188 DOI: 10.1016/j.yexcr.2007.04.005] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2007] [Revised: 03/30/2007] [Accepted: 04/03/2007] [Indexed: 12/28/2022]
Abstract
Filensin (BFSP1) and CP49 (BFSP2) represent two members of the IF protein superfamily that are thus far exclusively expressed in the eye lens. Mutations in both proteins cause lens cataract and careful consideration of the detail of these cataract phenotypes alerts us to several interesting features concerning the function of filensin (BFSP1) and CP49 (BFSP2) in the lens. With the first filensin (BFSP1) mutation now having been reported to cause a recessive cataract phenotype, there is the suggestion that the mutation could predispose heterozygote carriers to the early onset of age-related nuclear cataract. In the case of CP49 (BFSP2), there are now three unrelated families who have been identified with a common E233 Delta mutation. Very interestingly this is linked to myopia in one family. Despite the apparent phenotypic differences of the filensin (BFSP1) and CP49 (BFSP2) mutations, the data are still consistent with the beaded filament proteins being essential for lens function and specifically contributing to the optical properties of the lens. The fact that none of the mutations thus far reported affect either the conserved LNDR or TYRKLLEGE motifs that flank the central rod domain supports the view that this pair of IF proteins have unusual structural features and a distinctive assembly mechanism. The multiple sequence divergences suggest these proteins have been adapted to the specific functional requirements of lens fibre cells, a function that can be traced from squid to man.
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Affiliation(s)
- Ming-Der Perng
- School of Biological and Biomedical Sciences, The University of Durham, DH1 3LE, UK.
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Perng MD, Sandilands A, Kuszak J, Dahm R, Wegener A, Prescott AR, Quinlan RA. The intermediate filament systems in the eye lens. Methods Cell Biol 2005; 78:597-624. [PMID: 15646633 DOI: 10.1016/s0091-679x(04)78021-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/01/2023]
Affiliation(s)
- Ming Der Perng
- School of Biological and Biomedical Sciences, The University of Durham, Durham DH1 3LE, UK
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Sandilands A, Wang X, Hutcheson AM, James J, Prescott AR, Wegener A, Pekny M, Gong X, Quinlan RA. Bfsp2 mutation found in mouse 129 strains causes the loss of CP49' and induces vimentin-dependent changes in the lens fibre cell cytoskeleton. Exp Eye Res 2004; 78:875-89. [PMID: 15037121 DOI: 10.1016/j.exer.2003.09.028] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2003] [Accepted: 09/11/2003] [Indexed: 10/26/2022]
Abstract
Here we report the first natural mutation in the mouse Bfsp2 gene. Characterisation of mouse Bfsp2 in the 129X1/SvJ revealed a mutation that deleted the acceptor site of exon 2. This results in exon 1 being erroneously spliced to exon 3 causing a frameshift in the reading frame and the introduction of a stop codon at position 2 of exon 3 in the Bfsp2 transcript. RT-PCR studies of lens RNA isolated from 129S1/SvImJ, 129S2/SvPas and 129S4/SvJae strains confirmed the presence of this mutation in these diverse 129 strains and similar mutations were found in both CBA and 101 strains, but not in C3H or C57BL/6J mouse strains. This mutation is predicted to result in a severely truncated protein product called CP49, comprising essentially only exon 1, but polyclonal antibodies to CP49 failed to detect either full length or fragments of CP49 in extracts made from either 129S1/SvImJ or 129S4/SvJae suggesting that these 129 strains lack CP49 protein. Like the knockout of Bfsp2 reported recently, filensin protein levels and its proteolytic processing were altered also in the 129S1/SvImJ and 129S4/SvJae strains compared to C57BL/6J. Electron microscopy of the lens cytoskeleton from 129S2/SvPas revealed similar morphological changes in the cytoskeleton as compared to the CP49 knockout, with beaded and intermediate filaments being apparently replaced by poorly defined filament-like material. Vimentin was a key component of this residual material as shown by immunoelectron microscopy and by the generation of a CP49/vimentin double knockout mouse. This report of a natural mutation in Bfsp2 in the 129 and other mouse strains also has important implications for lens studies that have used the 129X1/SvJ strain in knockout strategies.
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Affiliation(s)
- Aileen Sandilands
- Department of Molecular and Cellular Pathology, University of Dundee, Dundee DD1 5EH Scotland, UK
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Sandilands A, Wang X, Hutcheson AM, James J, Prescott AR, Wegener A, Pekny M, Gong X, Quinlan RA. Bfsp2 mutation found in mouse 129 strains causes the loss of CP49 and induces vimentin-dependent changes in the lens fibre cell cytoskeleton. Exp Eye Res 2004; 78:109-23. [PMID: 14667833 DOI: 10.1016/j.exer.2003.09.001] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Here we report the first natural mutation in the mouse Bfsp2 gene. Characterisation of mouse Bfsp2 in the 129X1/SvJ revealed a mutation that deleted the acceptor site of exon 2. This results in exon 1 being erroneously spliced to exon 3 causing a frameshift in the reading frame and the introduction of a stop codon at position 2 of exon 3 in the Bfsp2 transcript. RT-PCR studies of lens RNA isolated from 129S1/SvImJ, 129S2/SvPas and 129S4/SvJae strains confirmed the presence of this mutation in these diverse 129 strains and similar mutations were found in both CBA and 101 strains, but not in C3H or C57BL/6J mouse strains. This mutation is predicted to result in a severely truncated protein product called CP49, comprising essentially only exon 1, but polyclonal antibodies to CP49 failed to detect either full length or fragments of CP49 in extracts made from either 129S1/SvImJ or 129S4/SvJae suggesting that these 129 strains lack CP49 protein. Like the knockout of Bfsp2 reported recently, filensin protein levels and its proteolytic processing were altered also in the 129S1/SvImJ and 129S4/SvJae strains compared to C57BL/6J. Electron microscopy of the lens cytoskeleton from 129S2/SvPas revealed similar morphological changes in the cytoskeleton as compared to the CP49 knockout, with beaded and intermediate filaments being apparently replaced by poorly defined filament-like material. Vimentin was a key component of this residual material as shown by immunoelectron microscopy and by the generation of a CP49/vimentin double knockout mouse. This report of a natural mutation in Bfsp2 in the 129 and other mouse strains also has important implications for lens studies that have used the 129X1/SvJ strain in knockout strategies.
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Affiliation(s)
- Aileen Sandilands
- Department of Molecular and Cellular Pathology, University of Dundee DD1 5EH, Scotland, UK.
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Ireland ME, Wallace P, Sandilands A, Poosch M, Kasper M, Graw J, Liu A, Maisel H, Prescott AR, Hutcheson AM, Goebel D, Quinlan RA. Up-regulation of novel intermediate filament proteins in primary fiber cells: an indicator of all vertebrate lens fiber differentiation? THE ANATOMICAL RECORD 2000; 258:25-33. [PMID: 10603445 DOI: 10.1002/(sici)1097-0185(20000101)258:1<25::aid-ar3>3.0.co;2-c] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The early embryonic development and expression patterns of the eye lens specific cytoskeletal proteins, CP49 and CP95, were determined for the chick and were found to be similar in both human and mouse. These proteins, as well as their homologs in other species, are obligate polymerization partners which form unique filamentous structures termed "beaded filaments." CP49 and CP95 appeared as protein products after 3 days of embryonic development in the chick during the elongation of primary fiber cells. Although limited data were obtained for human embryos at these early developmental timepoints, they were consistent with the interpretation that the up-regulation of these lens specific proteins began only after the initiation of lens vesicle closure. In situ hybridization with the mouse lens confirmed that message levels for beaded filament proteins were greatly elevated in differentiating primary fiber cells. Nuclease protection assays established that mRNA levels for CP49 remained relatively constant while CP95 mRNA levels increased once the process of secondary fiber formation was under way. Although present in relatively low abundance, the mRNA for a unique splice variant of CP49, CP49(INS), was also detected early in embryonic development and into adulthood. Peptide-specific antibodies directed against unique predicted sequences were able to confirm the protein expression of CP49(INS) in both embryonic and adult chick lens cells. These data present the first detailed study of the expression of CP49 and CP95 during early lens development. They suggest that the up-regulated expression of CP49 and CP95 could serve as pan-specific markers for all vertebrate lens fiber development.
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Affiliation(s)
- M E Ireland
- Department of Anatomy and Cell Biology, Wayne State University School of Medicine, Detroit, Michigan 48201, USA.
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Quinlan RA, Sandilands A, Procter JE, Prescott AR, Hutcheson AM, Dahm R, Gribbon C, Wallace P, Carter JM. The eye lens cytoskeleton. Eye (Lond) 1999; 13 ( Pt 3b):409-16. [PMID: 10627818 DOI: 10.1038/eye.1999.115] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
During lens cell differentiation there are a number of very characteristic morphological changes that occur. These include a 50- to 100-fold increase in cell length as the equatorial lens epithelial cells differentiate into fibre cells and the loss of the cellular organelles such as mitochondria, nuclei, Golgi apparatus and endoplasmic reticulum. Coincident with these changes are dramatic alterations in the organisation of the lens fibre cell cytoskeleton and in particular the lens-specific intermediate filament network comprising CP49 and filensin. Cell shape and cell polarisation as well as tissue integrity are all processes that depend upon the cytoskeleton and are therefore important to the lens. The unique aspects of the lenticular cytoskeleton are the subject of this review.
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Affiliation(s)
- R A Quinlan
- Department of Biochemistry, The University, Dundee, Scotland, UK.
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Mical TI, Monteiro MJ. The role of sequences unique to nuclear intermediate filaments in the targeting and assembly of human lamin B: evidence for lack of interaction of lamin B with its putative receptor. J Cell Sci 1998; 111 ( Pt 23):3471-85. [PMID: 9811562 DOI: 10.1242/jcs.111.23.3471] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The mechanism by which human nuclear lamin B is targeted and assembled has been studied by transfecting into mammalian cells lamin mutants deleted of three sequences unique to lamins. Nuclear lamins contain an extra 42 amino acids (aa) in their rod domains and NLS and CAAX motifs in their tail domains, which distinguishes them from cytoplasmic IF proteins. These three sequences act in concert to ensure correct temporal and spatial assembly of lamin B. Deletion of any one of these three sequences from lamin B did not significantly disrupt nuclear lamina targeting, but when two or more of these sequences were deleted, targeting was severely compromised. The CAAX motif is necessary for the efficient integration of lamin B into an already formed nuclear lamina, since lamin B CAAX- mutants had reduced targeting to the lamina when arrested in S phase of the cell cycle. CAAX-deficient mutant lamin B proteins were soluble and not associated with membranes at mitosis, proving that the CAAX motif is responsible for association of human lamin B with membranes. In addition, CAAX- mutant lamin B proteins fractionated independently of the lamin B-receptor (LBR), indicating that these two proteins do not bind directly to each other.
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Affiliation(s)
- T I Mical
- Department of Molecular Biology and Biophysics, Medical Biotechnology Center and Department of Neurology, Molecular and Cell Biology Graduate Program, University of Maryland, Baltimore, Maryland 21201, USA
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