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Lois-Bermejo I, González-Jiménez P, Duarte S, Pajares MA, Pérez-Sala D. Vimentin Tail Segments Are Differentially Exposed at Distinct Cellular Locations and in Response to Stress. Front Cell Dev Biol 2022; 10:908263. [PMID: 35769261 PMCID: PMC9235546 DOI: 10.3389/fcell.2022.908263] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2022] [Accepted: 05/17/2022] [Indexed: 01/13/2023] Open
Abstract
The intermediate filament protein vimentin plays a key role in cell signaling and stress sensing, as well as an integrator of cytoskeletal dynamics. The vimentin monomer consists of a central rod-like domain and intrinsically disordered head and tail domains. Although the organization of vimentin oligomers in filaments is beginning to be understood, the precise disposition of the tail region remains to be elucidated. Here we observed that electrophilic stress-induced condensation shielded vimentin from recognition by antibodies against specific segments of the tail domain. A detailed characterization revealed that vimentin tail segments are differentially exposed at distinct subcellular locations, both in basal and stress conditions. The 411–423 segment appeared accessible in all cell areas, correlating with vimentin abundance. In contrast, the 419–438 segment was more scantily recognized in perinuclear vimentin and lipoxidative stress-induced bundles, and better detected in peripheral filaments, where it appeared to protrude further from the filament core. These differences persisted in mitotic cells. Interestingly, both tail segments showed closer accessibility in calyculin A-treated cells and phosphomimetic mutants of the C-terminal region. Our results lead us to hypothesize the presence of at least two distinct arrangements of vimentin tail in cells: an “extended” conformation (accessible 419–438 segment), preferentially detected in peripheral areas with looser filaments, and a “packed” conformation (shielded 419–438 segment), preferentially detected at the cell center in robust filaments and lipoxidative stress-induced bundles. These different arrangements could be putatively interconverted by posttranslational modifications, contributing to the versatility of vimentin functions and/or interactions.
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Jang B, Kim M, Lee Y, Ishigami A, Kim Y, Choi E. Vimentin citrullination probed by a novel monoclonal antibody serves as a specific indicator for reactive astrocytes in neurodegeneration. Neuropathol Appl Neurobiol 2020; 46:751-769. [DOI: 10.1111/nan.12620] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2019] [Accepted: 03/23/2020] [Indexed: 01/11/2023]
Affiliation(s)
- B. Jang
- Ilsong Institute of Life Science Hallym University Anyang Gyeonggi‐doRepublic of Korea
| | - M.J. Kim
- Ilsong Institute of Life Science Hallym University Anyang Gyeonggi‐doRepublic of Korea
- Department of Biomedical Gerontology Graduate School of Hallym University Chuncheon Gangwon‐do Republic of Korea
| | - Y.J. Lee
- Ilsong Institute of Life Science Hallym University Anyang Gyeonggi‐doRepublic of Korea
| | - A. Ishigami
- Molecular Regulation of Aging Tokyo Metropolitan Institute of Gerontology Itabashi‐ku Tokyo Japan
| | - Y.S. Kim
- Ilsong Institute of Life Science Hallym University Anyang Gyeonggi‐doRepublic of Korea
- Department of Microbiology College of Medicine Hallym University Chuncheon Gangwon‐do Republic of Korea
| | - E.K. Choi
- Ilsong Institute of Life Science Hallym University Anyang Gyeonggi‐doRepublic of Korea
- Department of Biomedical Gerontology Graduate School of Hallym University Chuncheon Gangwon‐do Republic of Korea
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Duarte S, Viedma-Poyatos Á, Navarro-Carrasco E, Martínez AE, Pajares MA, Pérez-Sala D. Vimentin filaments interact with the actin cortex in mitosis allowing normal cell division. Nat Commun 2019; 10:4200. [PMID: 31519880 PMCID: PMC6744490 DOI: 10.1038/s41467-019-12029-4] [Citation(s) in RCA: 70] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2018] [Accepted: 08/09/2019] [Indexed: 01/27/2023] Open
Abstract
The vimentin network displays remarkable plasticity to support basic cellular functions and reorganizes during cell division. Here, we show that in several cell types vimentin filaments redistribute to the cell cortex during mitosis, forming a robust framework interwoven with cortical actin and affecting its organization. Importantly, the intrinsically disordered tail domain of vimentin is essential for this redistribution, which allows normal mitotic progression. A tailless vimentin mutant forms curly bundles, which remain entangled with dividing chromosomes leading to mitotic catastrophes or asymmetric partitions. Serial deletions of vimentin tail domain gradually impair cortical association and mitosis progression. Disruption of f-actin, but not of microtubules, causes vimentin bundling near the chromosomes. Pathophysiological stimuli, including HIV-protease and lipoxidation, induce similar alterations. Interestingly, full filament formation is dispensable for cortical association, which also occurs in vimentin particles. These results unveil implications of vimentin dynamics in cell division through its interplay with the actin cortex. The intermediate filament vimentin reorganizes during mitosis, but its molecular regulation and impact on the cell during cell division is unclear. Here, the authors show that vimentin filaments redistribute to the cell cortex during mitosis intertwining with and affecting actin organization.
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Affiliation(s)
- Sofia Duarte
- Department of Structural and Chemical Biology, Centro de Investigaciones Biológicas (CSIC), Ramiro de Maeztu 9, 28040, Madrid, Spain
| | - Álvaro Viedma-Poyatos
- Department of Structural and Chemical Biology, Centro de Investigaciones Biológicas (CSIC), Ramiro de Maeztu 9, 28040, Madrid, Spain
| | - Elena Navarro-Carrasco
- Department of Structural and Chemical Biology, Centro de Investigaciones Biológicas (CSIC), Ramiro de Maeztu 9, 28040, Madrid, Spain
| | - Alma E Martínez
- Department of Structural and Chemical Biology, Centro de Investigaciones Biológicas (CSIC), Ramiro de Maeztu 9, 28040, Madrid, Spain
| | - María A Pajares
- Department of Structural and Chemical Biology, Centro de Investigaciones Biológicas (CSIC), Ramiro de Maeztu 9, 28040, Madrid, Spain
| | - Dolores Pérez-Sala
- Department of Structural and Chemical Biology, Centro de Investigaciones Biológicas (CSIC), Ramiro de Maeztu 9, 28040, Madrid, Spain.
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4
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Hess JF, Budamagunta MS, Aziz A, FitzGerald PG, Voss JC. Electron paramagnetic resonance analysis of the vimentin tail domain reveals points of order in a largely disordered region and conformational adaptation upon filament assembly. Protein Sci 2014; 22:47-55. [PMID: 23109052 DOI: 10.1002/pro.2182] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2012] [Accepted: 10/15/2012] [Indexed: 01/27/2023]
Abstract
Very little data have been reported that describe the structure of the tail domain of any cytoplasmic intermediate filament (IF) protein. We report here the results of studies using site directed spin labeling and electron paramagnetic resonance (SDSL-EPR) to explore the structure and dynamics of the tail domain of human vimentin in tetramers (protofilaments) and filaments. The data demonstrate that in contrast to the vimentin head and rod domains, the tail domains are not closely apposed in protofilaments. However, upon assembly into intact IFs, several sites, including positions 445, 446, 451, and 452, the conserved "beta-site," become closely apposed, indicating dynamic changes in tail domain structure that accompany filament elongation. No evidence is seen for coiled-coil structure within the region studied, in either protofilaments or assembled filaments. EPR analysis also establishes that more than half of the tail domain is very flexible in both the assembly intermediate and the intact IF. However, by positioning the spin label at distinct sites, EPR is able to identify both the rod proximal region and sites flanking the beta-site motif as rigid locations within the tail. The rod proximal region is well assembled at the tetramer stage with only slight changes occurring during filament elongation. In contrast, at the beta site, the polypeptide backbone transitions from flexible in the assembly intermediate to much more rigid in the intact IF. These data support a model in which the distal tail domain structure undergoes significant conformational change during filament elongation and final assembly.
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Affiliation(s)
- John F Hess
- Department of Cell Biology and Human Anatomy, University of California, Davis, California 95616, USA
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5
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Guharoy M, Szabo B, Martos SC, Kosol S, Tompa P. Intrinsic Structural Disorder in Cytoskeletal Proteins. Cytoskeleton (Hoboken) 2013; 70:550-71. [DOI: 10.1002/cm.21118] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2013] [Revised: 05/26/2013] [Accepted: 05/29/2013] [Indexed: 12/11/2022]
Affiliation(s)
- Mainak Guharoy
- VIB Department of Structural Biology; Vrije Universiteit Brussel; Brussels Belgium
| | - Beata Szabo
- Institute of Enzymology; Research Centre for Natural Sciences, Hungarian Academy of Sciences; Budapest Hungary
| | | | - Simone Kosol
- VIB Department of Structural Biology; Vrije Universiteit Brussel; Brussels Belgium
| | - Peter Tompa
- VIB Department of Structural Biology; Vrije Universiteit Brussel; Brussels Belgium
- Institute of Enzymology; Research Centre for Natural Sciences, Hungarian Academy of Sciences; Budapest Hungary
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Joanne P, Chourbagi O, Agbulut O. [Desmin filaments and their disorganization associated with myofibrillar myopathies]. Biol Aujourdhui 2011; 205:163-77. [PMID: 21982405 DOI: 10.1051/jbio/2011016] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2011] [Indexed: 11/14/2022]
Abstract
Desmin, the muscle-specific intermediate filament protein, is one of the earliest markers expressed in all muscle tissues during development. It forms a three-dimensional scaffold around the myofibril Z-disc and connects the entire contractile apparatus to the subsarcolemmal cytoskeleton, the nuclei and other cytoplasmic organelles. Desmin is essential for tensile strength and muscle integrity. In humans, disorganization of the desmin network is associated with cardiac and/or skeletal myopathies characterized by accumulation of desmin-containing aggregates in the cells. Currently, 49 mutations have been identified in desmin gene. The majority of these mutations alter desmin filament assembly process through different molecular mechanisms and also its interaction with its protein partners. Here, we will give an overview of desmin network organization as well as the impact of desmin mutations on this process. Furthermore, we will discuss the different molecular mechanisms implicated in perturbation of the desmin filament assembly process.
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Affiliation(s)
- Pierre Joanne
- Université Paris Diderot, Sorbonne Paris Cité, France
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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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Lowrie DJ, Stickney JT, Ip W. Properties of the nonhelical end domains of vimentin suggest a role in maintaining intermediate filament network structure. J Struct Biol 2000; 132:83-94. [PMID: 11162730 DOI: 10.1006/jsbi.2000.4315] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
To investigate the functional role of the nonhelical domains of the intermediate filament (IF) protein vimentin, we carried out transient transfection of constructs encoding fusion proteins of these domains with enhanced green fluorescent protein (EGFP). Expression of these fusion proteins did not have any effect on the endogenous IF networks of transfected cells. However, the head domain-EGFP fusion protein localized almost exclusively to the nucleus. This localization could be disrupted in a reversible fashion by chilling cells. Furthermore, the head domain was capable of targeting to the nucleus a strictly cytoplasmic protein, pyruvate kinase. Thus, the vimentin head domain contains information that specifically directs proteins into the nucleus. In contrast, the nonhelical tail domain of vimentin, when expressed as a fusion protein with EGFP, was retained in the cytoplasm. Cytoplasmic retention of tail domain-containing fusion proteins appeared to be dependent on the integrity of the microtubule network. Our results are consistent with a proposal that the nonhelical end domains of vimentin are involved in maintaining an extended IF network by exerting oppositely directed forces along the filaments. The head domains exert a nuclear-directed force while the tail domains extend the IF network toward the cell periphery via a microtubule-dependent mechanism.
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Affiliation(s)
- D J Lowrie
- Department of Cell Biology, Neurobiology, and Anatomy, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0521, USA
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Asch WS, Schechter N. Plasticin, a type III neuronal intermediate filament protein, assembles as an obligate heteropolymer: implications for axonal flexibility. J Neurochem 2000; 75:1475-86. [PMID: 10987827 DOI: 10.1046/j.1471-4159.2000.0751475.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The assembly characteristics of the neuronal intermediate filament protein plasticin were studied in SW13 cells in the presence and absence of a cytoplasmic filament network. Full-length plasticin cannot polymerize into homopolymers in filament-less SW13c1.2Vim(-) cells but efficiently coassembles with vimentin in SW13c1.1Vim(-) cells. By cotransfecting plasticin and vimentin in SW13c1.1Vim(-) cells, we show that plasticin assembly requires vimentin in noncatalytic amounts. Differing effects on assembly were seen with point mutations of plasticin monomers that were analogous to the keratin mutations that cause epidermolysis bullosa simplex (EBS). In particular, plasticin monomers with point mutations analogous to those in EBS do not uniformly inhibit neurofilament (NF) network formation. A point mutation in the helix termination sequence resulted in complete filament aggregation when coexpressed with vimentin but showed limited coassembly with low- and medium-molecular-weight NF proteins (NF-L and NF-M, respectively). In transfected SW13c1.1Vim(+) cells, a point mutation in the first heptad of the alpha-helical coil region formed equal amounts of filaments, aggregates, and a mixture of filaments and aggregates. Furthermore, coexpression of this point mutation with NF-L and NF-M was associated with a shift toward increased numbers of aggregates. These results suggest that there are important structural differences in assembly properties between homologous fish and mammalian intermediate filament proteins. These structural differences may contribute to the distinctive growth characteristics of the teleost visual pathway.
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Affiliation(s)
- W S Asch
- Department of Biochemistry and Cell Biology, Health Sciences Center, State University of New York, Stony Brook, New York 11794, USA
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10
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Bellin RM, Sernett SW, Becker B, Ip W, Huiatt TW, Robson RM. Molecular characteristics and interactions of the intermediate filament protein synemin. Interactions with alpha-actinin may anchor synemin-containing heterofilaments. J Biol Chem 1999; 274:29493-9. [PMID: 10506213 DOI: 10.1074/jbc.274.41.29493] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Synemin is a cytoskeletal protein originally identified as an intermediate filament (IF)-associated protein because of its colocalization and copurification with the IF proteins desmin and vimentin in muscle cells. Our sequencing studies have shown that synemin is an unusually large member (1,604 residues, 182,187 Da) of the IF protein superfamily, with the majority of the molecule consisting of a long C-terminal tail domain. Molecular interaction studies demonstrate that purified synemin interacts with desmin, the major IF protein in mature muscle cells, and with alpha-actinin, an integral myofibrillar Z-line protein. Furthermore, expressed synemin rod and tail domains interact, respectively, with desmin and alpha-actinin. Analysis of endogenous protein expression in SW13 clonal lines reveals that synemin is coexpressed and colocalized with vimentin IFs in SW13.C1 vim+ cells but is absent in SW13.C2 vim- cells. Transfection studies indicate that synemin requires the presence of another IF protein, such as vimentin, in order to assemble into IFs. Taken in toto, our results suggest synemin functions as a component of heteropolymeric IFs and plays an important cytoskeletal cross-linking role by linking these IFs to other components of the cytoskeleton. Synemin in striated muscle cells may enable these heterofilaments to help link Z-lines of adjacent myofibrils and, thereby, play an important role in cytoskeletal integrity.
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Affiliation(s)
- R M Bellin
- Muscle Biology Group, Department of Biochemistry, Iowa State University, Ames, Iowa 50011-3260, USA
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11
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Ching GY, Liem RK. Roles of head and tail domains in alpha-internexin's self-assembly and coassembly with the neurofilament triplet proteins. J Cell Sci 1998; 111 ( Pt 3):321-33. [PMID: 9427681 DOI: 10.1242/jcs.111.3.321] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The roles of the head and tail domains of alpha-internexin, a type IV neuronal intermediate filament protein, in its self-assembly and coassemblies with neurofilament triplet proteins, were examined by transient transfections with deletion mutants in a non-neuronal cell line lacking an endogenous cytoplasmic intermediate filament network. The results from the self-assembly studies showed that the head domain was essential for alpha-internexin's ability to self-assemble into a filament network and the tail domain was important for establishing a proper filament network. The data from the coassembly studies demonstrated that alpha-internexin interacted differentially with the neurofilament triplet protein subunits. Wild-type NF-L or NF-M, but not NF-H, was able to complement and form a normal filament network with the tailless alpha-internexin mutant, the alpha-internexin head-deletion mutant, or the alpha-internexin mutant missing the entire tail and some amino-terminal portion of the head domain. In contrast, neither the tailless NF-L mutant nor the NF-L head-deletion mutant was able to form a normal filament network with any of these alpha-internexin deletion mutants. However, coassembly of the tailless NF-M mutant with the alpha-internexin head-deletion mutant and coassembly of the NF-M head-deletion mutant with the tailless alpha-internexin mutant resulted in the formation of a normal filament network. Thus, the coassembly between alpha-internexin and NF-M exhibits some unique characteristics previously not observed with other intermediate filament proteins: only one intact tail and one intact head are required for the formation of a normal filament network, and they can be present within the same partner or separately in two partners.
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Affiliation(s)
- G Y Ching
- Department of Pathology, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA
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Herrmann H, Häner M, Brettel M, Müller SA, Goldie KN, Fedtke B, Lustig A, Franke WW, Aebi U. Structure and assembly properties of the intermediate filament protein vimentin: the role of its head, rod and tail domains. J Mol Biol 1996; 264:933-53. [PMID: 9000622 DOI: 10.1006/jmbi.1996.0688] [Citation(s) in RCA: 255] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
We have investigated the functional role of the non-helical end domains of vimentin on its assembly properties using truncated Xenopus and human recombinant proteins. Removal of the amino-terminal "head" domain yielded a molecule that did not assemble into 10 nm filaments but remained in a soluble oligomeric particle form with a sedimentation coefficient considerably smaller than that of wild-type vimentin (Vim(wt)). In contrast, removal of the carboxy-terminal "tail" domain had no obvious effect on the sedimentation characteristics. In particular, sedimentation equilibrium analysis under low ionic strength conditions yielded oligomeric particle species of Mr 135,000 to 360,000, indistinguishable from those obtained with Vim(wt). When induced to form filaments from this state by rapid dilution into filament forming buffer, Vim(wt) and Vim(deltaT) protein generated similar viscosity profiles. However, as determined by scanning transmission electron microscopy, under these conditions Vim(deltaT) formed filaments of heterogeneous diameter, corresponding to various distinct mass-per-length (MPL) values: whereas Vim(wt) yielded MPL values peaking between 40 and 45 kDa/nm, Vim(deltaT) filaments produced histograms which could be fitted by three Gaussian curves peaking between 37 and 131 kDa/nm. In contrast, when dialyzed against, instead of being rapidly diluted into, filament forming buffer, Vim(deltaT) gave histograms with one major peak at about 54 kDa/nm. The MPL heterogeneity observed for Vim(deltaT) was already evident at the earliest stages of assembly. For example, ten seconds after initiation, "unit-length" filament segments (58 to 63 nm) were formed with both wt and deltaT proteins, but the diameters were considerably larger for Vim(deltaT) compared to Vim(wt) (20(+/- 3) nm versus 16(+/- 3)nm), indicating a distinct role of the carboxy-terminal tail domain in the width control during unit-length filament formation. Despite this difference both Vim(deltaT) and Vim(wt) filaments appeared to grow stepwise in a modular fashion from such unit-length filament segments. This suggests that assembly occurred by a principally similar mechanism involving the end-on-fusion or annealing of unit-length filaments.
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Affiliation(s)
- H Herrmann
- Division of Cell Biology, German Cancer Research Center, Heidelberg
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Meng JJ, Khan S, Ip W. Intermediate filament protein domain interactions as revealed by two-hybrid screens. J Biol Chem 1996; 271:1599-604. [PMID: 8576158 DOI: 10.1074/jbc.271.3.1599] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
All intermediate filament proteins possess three distinct domains: heads, rod and tail, and subdomains within the rod called helices 1A, 1B, 2A, and 2B. Subunit packing within a filament is a consequence of interactions among these domains. Several such interactions are known, but probably many more contribute to stabilizing filament structure. We examined a number of such potential interactions using the yeast two-hybrid system. Domains or subdomains of murine vimentin, a Type III intermediate filament protein, were fused with either the DNA-binding or trans-activating domain of GAL4, a transcription factor. Interaction between the vimentin domains/subdomains functionally reconstituted GAL4, thereby activating transcription of a GAL1-LacZ reporter gene. The oligomeric state at which the interactions took place, i.e. whether the domains/subdomains were dimeric or tetrameric as they interacted, was also determined. These studies revealed a number of interesting interactions, among which was a strong homotypic binding to helix 2B to form tetramers. They also demonstrated a lack of interaction among others expected to do so based on current structural models. From these results we deduced which of the candidates for interactions, suggested by current models, were true protein-protein interactions and which represented nearest-neighbors only. Thus, the A11 and A22 modes of molecular alignment identified by Steinert et al. (Steinert, P. M., Marekov, L. N., Fraser, R. D. B., and Parry, D. A. D. (1993) J. Mol. Biol. 230, 436-452) are probably true interactions, whereas the A12 and ACN modes may describe adjacent but non-interacting molecules.
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Affiliation(s)
- J J Meng
- Department of Cell Biology, Neurobiology, and Anatomy, University of Cincinnati College of Medicine, Ohio 45267-0521, USA
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