1
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Onwunma J, Binsabaan S, Allen SP, Sankaran B, Wohlever ML. The structural and biophysical basis of substrate binding to the hydrophobic groove in Ubiquilin Sti1 domains. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.07.10.602902. [PMID: 39026758 PMCID: PMC11257586 DOI: 10.1101/2024.07.10.602902] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/20/2024]
Abstract
Ubiquilins are a family of cytosolic proteins that ferry ubiquitinated substrates to the proteasome for degradation. Recent work has demonstrated that Ubiquilins can also act as molecular chaperones, utilizing internal Sti1 domains to directly bind to hydrophobic sequences. Ubiquilins are associated with several neurodegenerative diseases with point mutations in UBQLN2 causing dominant, X-linked Amyotrophic Lateral Sclerosis (ALS). The molecular basis of Ubiquilin chaperone activity and how ALS mutations in the Sti1 domains affect Ubiquilin activity are poorly understood. This study presents the first crystal structure of the Sti1 domain from a fungal Ubiquilin homolog bound to a transmembrane domain (TMD). The structure reveals that two Sti1 domains form a head-to-head dimer, creating a hydrophobic cavity that accommodates two TMDs. Mapping the UBQLN2 sequence onto the structure shows that several ALS mutations are predicted to disrupt the hydrophobic groove. Using a newly developed competitive binding assay, we show that Ubiquilins preferentially bind to hydrophobic substrates with low helical propensity, motifs that are enriched in both substrates and in Ubiquilins. This study provides insights into the molecular and structural basis for Ubiquilin substrate binding, with broad implications for the role of the Sti1 domain in phase separation and ALS.
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Affiliation(s)
- Joan Onwunma
- Previously at University of Toledo, Department of Chemistry & Biochemistry
| | | | - Shawn P Allen
- Previously at University of Toledo, Department of Chemistry & Biochemistry
- University of Pittsburgh, Department of Cell Biology
| | - Banumathi Sankaran
- Lawrence Berkley National Lab, Berkeley Center for Structural Biology, Molecular Biophysics and Integrated Bioimaging
| | - Matthew L Wohlever
- Previously at University of Toledo, Department of Chemistry & Biochemistry
- University of Pittsburgh, Department of Cell Biology
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2
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Dao TP, Rajendran A, Galagedera SKK, Haws W, Castañeda CA. Short disordered termini and proline-rich domain are major regulators of UBQLN1/2/4 phase separation. Biophys J 2024; 123:1449-1457. [PMID: 38041404 PMCID: PMC11163289 DOI: 10.1016/j.bpj.2023.11.3401] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2023] [Revised: 11/28/2023] [Accepted: 11/29/2023] [Indexed: 12/03/2023] Open
Abstract
Highly homologous ubiquitin-binding shuttle proteins UBQLN1, UBQLN2, and UBQLN4 differ in both their specific protein quality control functions and their propensities to localize to stress-induced condensates, cellular aggregates, and aggresomes. We previously showed that UBQLN2 phase separates in vitro, and that the phase separation propensities of UBQLN2 deletion constructs correlate with their ability to form condensates in cells. Here, we demonstrated that full-length UBQLN1, UBQLN2, and UBQLN4 exhibit distinct phase behaviors in vitro. Strikingly, UBQLN4 phase separates at a much lower saturation concentration than UBQLN1. However, neither UBQLN1 nor UBQLN4 phase separates with a strong temperature dependence, unlike UBQLN2. We determined that the temperature-dependent phase behavior of UBQLN2 stems from its unique proline-rich region, which is absent in the other UBQLNs. We found that the short N-terminal disordered regions of UBQLN1, UBQLN2, and UBQLN4 inhibit UBQLN phase separation via electrostatics interactions. Charge variants of the N-terminal regions exhibit altered phase behaviors. Consistent with the sensitivity of UBQLN phase separation to the composition of the N-terminal regions, epitope tags placed on the N-termini of the UBQLNs tune phase separation. Overall, our in vitro results have important implications for studies of UBQLNs in cells, including the identification of phase separation as a potential mechanism to distinguish the cellular roles of UBQLNs and the need to apply caution when using epitope tags to prevent experimental artifacts.
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Affiliation(s)
- Thuy P Dao
- Departments of Biology and Chemistry, Syracuse University, Syracuse, New York
| | - Anitha Rajendran
- Departments of Biology and Chemistry, Syracuse University, Syracuse, New York
| | | | - William Haws
- Departments of Biology and Chemistry, Syracuse University, Syracuse, New York
| | - Carlos A Castañeda
- Departments of Biology and Chemistry, Syracuse University, Syracuse, New York; Interdisciplinary Neuroscience Program, Syracuse University, Syracuse, New York; BioInspired Institute, Syracuse University, Syracuse, New York.
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3
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Waite KA, Vontz G, Lee SY, Roelofs J. Proteasome condensate formation is driven by multivalent interactions with shuttle factors and ubiquitin chains. Proc Natl Acad Sci U S A 2024; 121:e2310756121. [PMID: 38408252 PMCID: PMC10927584 DOI: 10.1073/pnas.2310756121] [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: 06/26/2023] [Accepted: 01/26/2024] [Indexed: 02/28/2024] Open
Abstract
Stress conditions can cause the relocalization of proteasomes to condensates in yeast and mammalian cells. The interactions that facilitate the formation of proteasome condensates, however, are unclear. Here, we show that the formation of proteasome condensates in yeast depends on ubiquitin chains together with the proteasome shuttle factors Rad23 and Dsk2. These shuttle factors colocalize to these condensates. Strains deleted for the third shuttle factor gene, DDI1, show proteasome condensates in the absence of cellular stress, consistent with the accumulation of substrates with long K48-linked ubiquitin chains that accumulate in this mutant. We propose a model where the long K48-linked ubiquitin chains function as a scaffold for the ubiquitin-binding domains of the shuttle factors and the proteasome, allowing for the multivalent interactions that further drive condensate formation. Indeed, we determined different intrinsic ubiquitin receptors of the proteasome-Rpn1, Rpn10, and Rpn13-and the Ubl domains of Rad23 and Dsk2 are critical under different condensate-inducing conditions. In all, our data support a model where the cellular accumulation of substrates with long ubiquitin chains, potentially due to reduced cellular energy, allows for proteasome condensate formation. This suggests that proteasome condensates are not simply for proteasome storage, but function to sequester soluble ubiquitinated substrates together with inactive proteasomes.
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Affiliation(s)
- Kenrick A. Waite
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS66160
| | - Gabrielle Vontz
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS66160
| | - Stella Y. Lee
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS66160
| | - Jeroen Roelofs
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS66160
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4
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Holehouse AS, Kragelund BB. The molecular basis for cellular function of intrinsically disordered protein regions. Nat Rev Mol Cell Biol 2024; 25:187-211. [PMID: 37957331 DOI: 10.1038/s41580-023-00673-0] [Citation(s) in RCA: 55] [Impact Index Per Article: 55.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/26/2023] [Indexed: 11/15/2023]
Abstract
Intrinsically disordered protein regions exist in a collection of dynamic interconverting conformations that lack a stable 3D structure. These regions are structurally heterogeneous, ubiquitous and found across all kingdoms of life. Despite the absence of a defined 3D structure, disordered regions are essential for cellular processes ranging from transcriptional control and cell signalling to subcellular organization. Through their conformational malleability and adaptability, disordered regions extend the repertoire of macromolecular interactions and are readily tunable by their structural and chemical context, making them ideal responders to regulatory cues. Recent work has led to major advances in understanding the link between protein sequence and conformational behaviour in disordered regions, yet the link between sequence and molecular function is less well defined. Here we consider the biochemical and biophysical foundations that underlie how and why disordered regions can engage in productive cellular functions, provide examples of emerging concepts and discuss how protein disorder contributes to intracellular information processing and regulation of cellular function.
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Affiliation(s)
- Alex S Holehouse
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St Louis, MO, USA.
- Center for Biomolecular Condensates, Washington University in St Louis, St Louis, MO, USA.
| | - Birthe B Kragelund
- REPIN, Structural Biology and NMR Laboratory, Department of Biology, University of Copenhagen, Copenhagen, Denmark.
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5
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Moses D, Guadalupe K, Yu F, Flores E, Perez AR, McAnelly R, Shamoon NM, Kaur G, Cuevas-Zepeda E, Merg AD, Martin EW, Holehouse AS, Sukenik S. Structural biases in disordered proteins are prevalent in the cell. Nat Struct Mol Biol 2024; 31:283-292. [PMID: 38177684 PMCID: PMC10873198 DOI: 10.1038/s41594-023-01148-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2022] [Accepted: 10/04/2023] [Indexed: 01/06/2024]
Abstract
Intrinsically disordered proteins and protein regions (IDPs) are prevalent in all proteomes and are essential to cellular function. Unlike folded proteins, IDPs exist in an ensemble of dissimilar conformations. Despite this structural plasticity, intramolecular interactions create sequence-specific structural biases that determine an IDP ensemble's three-dimensional shape. Such structural biases can be key to IDP function and are often measured in vitro, but whether those biases are preserved inside the cell is unclear. Here we show that structural biases in IDP ensembles found in vitro are recapitulated inside human-derived cells. We further reveal that structural biases can change in a sequence-dependent manner due to changes in the intracellular milieu, subcellular localization, and intramolecular interactions with tethered well-folded domains. We propose that the structural sensitivity of IDP ensembles can be leveraged for biological function, can be the underlying cause of IDP-driven pathology or can be used to design disorder-based biosensors and actuators.
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Affiliation(s)
- David Moses
- Department of Chemistry and Biochemistry, University of California, Merced, Merced, CA, USA
- Center for Cellular and Biomolecular Machines, University of California, Merced, Merced, CA, USA
| | - Karina Guadalupe
- Department of Chemistry and Biochemistry, University of California, Merced, Merced, CA, USA
- Center for Cellular and Biomolecular Machines, University of California, Merced, Merced, CA, USA
| | - Feng Yu
- Center for Cellular and Biomolecular Machines, University of California, Merced, Merced, CA, USA
- Quantitative and Systems Biology Program, University of California, Merced, Merced, CA, USA
| | - Eduardo Flores
- Department of Chemistry and Biochemistry, University of California, Merced, Merced, CA, USA
- Center for Cellular and Biomolecular Machines, University of California, Merced, Merced, CA, USA
| | - Anthony R Perez
- Department of Chemistry and Biochemistry, University of California, Merced, Merced, CA, USA
- Center for Cellular and Biomolecular Machines, University of California, Merced, Merced, CA, USA
| | - Ralph McAnelly
- Department of Chemistry and Biochemistry, University of California, Merced, Merced, CA, USA
| | - Nora M Shamoon
- Center for Cellular and Biomolecular Machines, University of California, Merced, Merced, CA, USA
- California State University, Stanislaus, Turlock, CA, USA
| | - Gagandeep Kaur
- Department of Chemistry and Biochemistry, University of California, Merced, Merced, CA, USA
| | | | - Andrea D Merg
- Department of Chemistry and Biochemistry, University of California, Merced, Merced, CA, USA
- Center for Cellular and Biomolecular Machines, University of California, Merced, Merced, CA, USA
| | - Erik W Martin
- Department of Structural Biology, St Jude Children's Research Hospital, Memphis, TN, USA
- Dewpoint Therapeutics, Boston, MA, USA
| | - Alex S Holehouse
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO, USA
- Center for Science and Engineering of Living Systems, Washington University in St. Louis, St. Louis, MO, USA
| | - Shahar Sukenik
- Department of Chemistry and Biochemistry, University of California, Merced, Merced, CA, USA.
- Center for Cellular and Biomolecular Machines, University of California, Merced, Merced, CA, USA.
- Quantitative and Systems Biology Program, University of California, Merced, Merced, CA, USA.
- Health Sciences Research Institute, University of California, Merced, Merced, CA, USA.
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6
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Mohanty P, Rizuan A, Kim YC, Fawzi NL, Mittal J. A complex network of interdomain interactions underlies the conformational ensemble of monomeric TDP-43 and modulates its phase behavior. Protein Sci 2024; 33:e4891. [PMID: 38160320 PMCID: PMC10804676 DOI: 10.1002/pro.4891] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2023] [Revised: 12/07/2023] [Accepted: 12/28/2023] [Indexed: 01/03/2024]
Abstract
TAR DNA-binding protein 43 (TDP-43) is a multidomain protein involved in the regulation of RNA metabolism, and its aggregates have been observed in neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Numerous studies indicate TDP-43 can undergo liquid-liquid phase separation (LLPS) in vitro and is a component of biological condensates. Homo-oligomerization via the folded N-terminal domain (aa:1-77) and the conserved helical region (aa:319-341) of the disordered, C-terminal domain is found to be an important driver of TDP-43 phase separation. However, a comprehensive molecular view of TDP-43 phase separation, particularly regarding the nature of heterodomain interactions, is lacking due to the challenges associated with its stability and purification. Here, we utilize all-atom and coarse-grained (CG) molecular dynamics (MD) simulations to uncover the network of interdomain interactions implicated in TDP-43 phase separation. All-atom simulations uncovered the presence of transient, interdomain interactions involving flexible linkers, RNA-recognition motif (RRM) domains and a charged segment of disordered C-terminal domain (CTD). CG simulations indicate these inter-domain interactions which affect the conformational landscape of TDP-43 in the dilute phase are also prevalent in the condensed phase. Finally, sequence and surface charge distribution analysis coupled with all-atom simulations (at high salt) confirmed that the transient interdomain contacts are predominantly electrostatic in nature. Overall, our findings from multiscale simulations lead to a greater appreciation of the complex interaction network underlying the structural landscape and phase separation of TDP-43.
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Affiliation(s)
- Priyesh Mohanty
- Artie McFerrin Department of Chemical EngineeringTexas A&M UniversityCollege StationTexasUSA
| | - Azamat Rizuan
- Artie McFerrin Department of Chemical EngineeringTexas A&M UniversityCollege StationTexasUSA
| | - Young C. Kim
- Naval Research LaboratoryCenter for Materials Physics and TechnologyWashingtonDistrict of ColumbiaUSA
| | - Nicolas L. Fawzi
- Department of Molecular Biology, Cell Biology and BiochemistryProvidenceRhode IslandUSA
| | - Jeetain Mittal
- Artie McFerrin Department of Chemical EngineeringTexas A&M UniversityCollege StationTexasUSA
- Department of ChemistryTexas A&M UniversityCollege StationTexasUSA
- Interdisciplinary Graduate Program in Genetics and GenomicsTexas A&M UniversityCollege StationTexasUSA
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7
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Arai M, Suetaka S, Ooka K. Dynamics and interactions of intrinsically disordered proteins. Curr Opin Struct Biol 2024; 84:102734. [PMID: 38039868 DOI: 10.1016/j.sbi.2023.102734] [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: 07/31/2023] [Revised: 10/27/2023] [Accepted: 10/30/2023] [Indexed: 12/03/2023]
Abstract
Intrinsically disordered proteins (IDPs) are widespread in eukaryotes and participate in a variety of important cellular processes. Numerous studies using state-of-the-art experimental and theoretical methods have advanced our understanding of IDPs and revealed that disordered regions engage in a large repertoire of intra- and intermolecular interactions through their conformational dynamics, thereby regulating many intracellular functions in concert with folded domains. The mechanisms by which IDPs interact with their partners are diverse, depending on their conformational propensities, and include induced fit, conformational selection, and their mixtures. In addition, IDPs are implicated in many diseases, and progress has been made in designing inhibitors of IDP-mediated interactions. Here we review these recent advances with a focus on the dynamics and interactions of IDPs.
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Affiliation(s)
- Munehito Arai
- Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan; Komaba Organization for Educational Excellence, College of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan; Department of Physics, Graduate School of Science, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan.
| | - Shunji Suetaka
- Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
| | - Koji Ooka
- Komaba Organization for Educational Excellence, College of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
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8
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Sipko EL, Chappell GF, Berlow RB. Multivalency emerges as a common feature of intrinsically disordered protein interactions. Curr Opin Struct Biol 2024; 84:102742. [PMID: 38096754 DOI: 10.1016/j.sbi.2023.102742] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2023] [Revised: 11/20/2023] [Accepted: 11/22/2023] [Indexed: 02/09/2024]
Abstract
Intrinsically disordered proteins (IDPs) use their unique molecular properties and conformational plasticity to interact with cellular partners in a wide variety of biological contexts. Multivalency is an important feature of IDPs that allows for utilization of an expanded toolkit for interactions with other macromolecules and confers additional complexity to molecular recognition processes. Recent studies have offered insights into how multivalent interactions of IDPs enable responsive and sensitive regulation in the context of transcription and cellular signaling. Multivalency is also widely recognized as an important feature of IDP interactions that mediate formation of biomolecular condensates. We highlight recent examples of multivalent interactions of IDPs across diverse contexts to illustrate the breadth of biological processes that utilize multivalency in molecular interactions.
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Affiliation(s)
- Emily L Sipko
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Garrett F Chappell
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Rebecca B Berlow
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA; Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
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9
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Galagedera SKK, Dao TP, Enos SE, Chaudhuri A, Schmit JD, Castañeda CA. Polyubiquitin ligand-induced phase transitions are optimized by spacing between ubiquitin units. Proc Natl Acad Sci U S A 2023; 120:e2306638120. [PMID: 37824531 PMCID: PMC10589717 DOI: 10.1073/pnas.2306638120] [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: 04/25/2023] [Accepted: 09/01/2023] [Indexed: 10/14/2023] Open
Abstract
Biomolecular condensates form via multivalent interactions among key macromolecules and are regulated through ligand binding and/or posttranslational modifications. One such modification is ubiquitination, the covalent addition of ubiquitin (Ub) or polyubiquitin chains to target macromolecules. Specific interactions between polyubiquitin chains and partner proteins, including hHR23B, NEMO, and UBQLN2, regulate condensate assembly or disassembly. Here, we used a library of designed polyubiquitin hubs and UBQLN2 as model systems for determining the driving forces of ligand-mediated phase transitions. Perturbations to either the UBQLN2-binding surface of Ub or the spacing between Ub units reduce the ability of hubs to modulate UBQLN2 phase behavior. By developing an analytical model based on polyphasic linkage principles that accurately described the effects of different hubs on UBQLN2 phase separation, we determined that introduction of Ub to UBQLN2 condensates incurs a significant inclusion energetic penalty. This penalty antagonizes the ability of polyUb hubs to scaffold multiple UBQLN2 molecules and cooperatively amplify phase separation. The extent to which polyubiquitin hubs promote UBQLN2 phase separation is encoded in the spacings between Ub units. This spacing is modulated by chains of different linkages and designed chains of different architectures, thus illustrating how the ubiquitin code regulates functionality via the emergent properties of the condensate. The spacing in naturally occurring linear polyubiquitin chains is already optimized to promote phase separation with UBQLN2. We expect our findings to extend to other condensates, emphasizing the importance of ligand properties, including concentration, valency, affinity, and spacing between binding sites in studies and designs of condensates.
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Affiliation(s)
- Sarasi K. K. Galagedera
- Department of Biology, Syracuse University, Syracuse, NY13244
- Department of Chemistry, Syracuse University, Syracuse, NY13244
| | - Thuy P. Dao
- Department of Biology, Syracuse University, Syracuse, NY13244
- Department of Chemistry, Syracuse University, Syracuse, NY13244
| | - Suzanne E. Enos
- Department of Biology, Syracuse University, Syracuse, NY13244
- Department of Chemistry, Syracuse University, Syracuse, NY13244
| | - Antara Chaudhuri
- Department of Biology, Syracuse University, Syracuse, NY13244
- Department of Chemistry, Syracuse University, Syracuse, NY13244
| | - Jeremy D. Schmit
- Department of Physics, Kansas State University, Manhattan, KS66506
| | - Carlos A. Castañeda
- Department of Biology, Syracuse University, Syracuse, NY13244
- Department of Chemistry, Syracuse University, Syracuse, NY13244
- Interdisciplinary Neuroscience Program, Syracuse University, Syracuse, NY13244
- BioInspired Institute, Syracuse University, Syracuse, NY13244
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10
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Dao TP, Rajendran A, Galagedera SKK, Haws W, Castañeda CA. Short N-terminal disordered regions and the proline-rich domain are major regulators of phase transitions for full-length UBQLN1, UBQLN2 and UBQLN4. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.09.27.559790. [PMID: 37808720 PMCID: PMC10557701 DOI: 10.1101/2023.09.27.559790] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/10/2023]
Abstract
Highly homologous ubiquitin-binding shuttle proteins UBQLN1, UBQLN2 and UBQLN4 differ in both their specific protein quality control functions and their propensities to localize to stress-induced condensates, cellular aggregates and aggresomes. We previously showed that UBQLN2 phase separates in vitro, and that the phase separation propensities of UBQLN2 deletion constructs correlate with their ability to form condensates in cells. Here, we demonstrated that full-length UBQLN1, UBQLN2 and UBQLN4 exhibit distinct phase behaviors in vitro. Strikingly, UBQLN4 phase separates at a much lower saturation concentration than UBQLN1. However, neither UBQLN1 nor UBQLN4 phase separates with a strong temperature dependence, unlike UBQLN2. We determined that the temperature-dependent phase behavior of UBQLN2 stems from its unique proline-rich (Pxx) region, which is absent in the other UBQLNs. We found that the short N-terminal disordered regions of UBQLN1, UBQLN2 and UBQLN4 inhibit UBQLN phase separation via electrostatics interactions. Charge variants of the N-terminal regions exhibit altered phase behaviors. Consistent with the sensitivity of UBQLN phase separation to the composition of the N-terminal regions, epitope tags placed on the N-termini of the UBQLNs tune phase separation. Overall, our in vitro results have important implications for studies of UBQLNs in cells, including the identification of phase separation as a potential mechanism to distinguish the cellular roles of UBQLNs, and the need to apply caution when using epitope tags to prevent experimental artifacts.
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Affiliation(s)
- Thuy P. Dao
- Departments of Biology and Chemistry, Syracuse University, Syracuse, NY 13244, USA
| | - Anitha Rajendran
- Departments of Biology and Chemistry, Syracuse University, Syracuse, NY 13244, USA
| | | | - William Haws
- Departments of Biology and Chemistry, Syracuse University, Syracuse, NY 13244, USA
| | - Carlos A. Castañeda
- Departments of Biology and Chemistry, Syracuse University, Syracuse, NY 13244, USA
- Interdisciplinary Neuroscience Program, Syracuse University, Syracuse, NY 13244, USA
- BioInspired Institute, Syracuse University, Syracuse, NY 13244, USA
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11
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Robb CG, Dao TP, Ujma J, Castañeda CA, Beveridge R. Ion Mobility Mass Spectrometry Unveils Global Protein Conformations in Response to Conditions that Promote and Reverse Liquid-Liquid Phase Separation. J Am Chem Soc 2023. [PMID: 37276246 DOI: 10.1021/jacs.3c00756] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Liquid-liquid phase separation (LLPS) is a process by which biomacromolecules, particularly proteins, condense into a dense phase that resembles liquid droplets. Dysregulation of LLPS is implicated in disease, yet the relationship between protein conformational changes and LLPS remains difficult to discern. This is due to the high flexibility and disordered nature of many proteins that phase separate under physiological conditions and their tendency to oligomerize. Here, we demonstrate that ion mobility mass spectrometry (IM-MS) overcomes these limitations. We used IM-MS to investigate the conformational states of full-length ubiquilin-2 (UBQLN2) protein, LLPS of which is driven by high-salt concentration and reversed by noncovalent interactions with ubiquitin (Ub). IM-MS revealed that UBQLN2 exists as a mixture of monomers and dimers and that increasing salt concentration causes the UBQLN2 dimers to undergo a subtle shift toward extended conformations. UBQLN2 binds to Ub in 2:1 and 2:2 UBQLN2/Ub complexes, which have compact geometries compared to free UBQLN2 dimers. Together, these results suggest that extended conformations of UBQLN2 are correlated with UBQLN2's ability to phase separate. Overall, delineating protein conformations that are implicit in LLPS will greatly increase understanding of the phase separation process, both in normal cell physiology and disease states.
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Affiliation(s)
- Christina Glen Robb
- Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow G1 1XL, U.K
| | - Thuy P Dao
- Departments of Biology and Chemistry, BioInspired Institute, Syracuse University, Syracuse, New York 13244, United States
| | - Jakub Ujma
- Waters Corporation, Stamford Avenue, Altrincham Road, Wilmslow SK9 4AX, U.K
| | - Carlos A Castañeda
- Departments of Biology and Chemistry, BioInspired Institute, Syracuse University, Syracuse, New York 13244, United States
| | - Rebecca Beveridge
- Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow G1 1XL, U.K
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12
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Ciancone AM, Seo KW, Chen M, Borne AL, Libby AH, Bai DL, Kleiner RE, Hsu KL. Global Discovery of Covalent Modulators of Ribonucleoprotein Granules. J Am Chem Soc 2023; 145:11056-11066. [PMID: 37159397 PMCID: PMC10392812 DOI: 10.1021/jacs.3c00165] [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] [Indexed: 05/11/2023]
Abstract
Stress granules (SGs) and processing-bodies (PBs, P-bodies) are ubiquitous and widely studied ribonucleoprotein (RNP) granules involved in cellular stress response, viral infection, and the tumor microenvironment. While proteomic and transcriptomic investigations of SGs and PBs have provided insights into molecular composition, chemical tools to probe and modulate RNP granules remain lacking. Herein, we combine an immunofluorescence (IF)-based phenotypic screen with chemoproteomics to identify sulfonyl-triazoles (SuTEx) capable of preventing or inducing SG and PB formation through liganding of tyrosine (Tyr) and lysine (Lys) sites in stressed cells. Liganded sites were enriched for RNA-binding and protein-protein interaction (PPI) domains, including several sites found in RNP granule-forming proteins. Among these, we functionally validate G3BP1 Y40, located in the NTF2 dimerization domain, as a ligandable site that can disrupt arsenite-induced SG formation in cells. In summary, we present a chemical strategy for the systematic discovery of condensate-modulating covalent small molecules.
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Affiliation(s)
- Anthony M. Ciancone
- Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904, United States
| | - Kyung W. Seo
- Department of Chemistry, Princeton University, Princeton, NJ 08544, USA
| | - Miaomiao Chen
- Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904, United States
| | - Adam L. Borne
- Department of Pharmacology, University of Virginia School of Medicine, Charlottesville, Virginia 22908, United States
| | - Adam H. Libby
- Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904, United States
- University of Virginia Cancer Center, University of Virginia, Charlottesville, VA 22903, USA
| | - Dina L. Bai
- Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904, United States
| | - Ralph E. Kleiner
- Department of Chemistry, Princeton University, Princeton, NJ 08544, USA
| | - Ku-Lung Hsu
- Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904, United States
- Department of Pharmacology, University of Virginia School of Medicine, Charlottesville, Virginia 22908, United States
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Virginia 22908, United States
- University of Virginia Cancer Center, University of Virginia, Charlottesville, VA 22903, USA
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13
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Galagedera SKK, Dao TP, Enos SE, Chaudhuri A, Schmit JD, Castañeda CA. Decoding optimal ligand design for multicomponent condensates. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.03.13.532222. [PMID: 36993708 PMCID: PMC10054939 DOI: 10.1101/2023.03.13.532222] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/29/2023]
Abstract
Biomolecular condensates form via multivalent interactions among key macromolecules and are regulated through ligand binding and/or post-translational modifications. One such modification is ubiquitination, the covalent addition of ubiquitin (Ub) or polyubiquitin chains to target macromolecules for various cellular processes. Specific interactions between polyubiquitin chains and partner proteins, including hHR23B, NEMO, and UBQLN2, regulate condensate assembly or disassembly. Here, we used a library of designed polyubiquitin hubs and UBQLN2 as model systems for determining the driving forces of ligand-mediated phase transitions. Perturbations to the UBQLN2-binding surface of Ub or deviations from the optimal spacing between Ub units reduce the ability of hubs to modulate UBQLN2 phase behavior. By developing an analytical model that accurately described the effects of different hubs on UBQLN2 phase diagrams, we determined that introduction of Ub to UBQLN2 condensates incurs a significant inclusion energetic penalty. This penalty antagonizes the ability of polyUb hubs to scaffold multiple UBQLN2 molecules and cooperatively amplify phase separation. Importantly, the extent to which polyubiquitin hubs can promote UBQLN2 phase separation are encoded in the spacings between Ub units as found for naturally-occurring chains of different linkages and designed chains of different architectures, thus illustrating how the ubiquitin code regulates functionality via the emergent properties of the condensate. We expect our findings to extend to other condensates necessitating the consideration of ligand properties, including concentration, valency, affinity, and spacing between binding sites in studies and designs of condensates.
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Affiliation(s)
| | - Thuy P. Dao
- Departments of Biology and Chemistry, Syracuse University, Syracuse, NY 13244, USA
| | - Suzanne E. Enos
- Departments of Biology and Chemistry, Syracuse University, Syracuse, NY 13244, USA
| | - Antara Chaudhuri
- Departments of Biology and Chemistry, Syracuse University, Syracuse, NY 13244, USA
| | - Jeremy D. Schmit
- Department of Physics, Kansas State University, Manhattan, KS 66506, USA
| | - Carlos A. Castañeda
- Departments of Biology and Chemistry, Syracuse University, Syracuse, NY 13244, USA
- Interdisciplinary Neuroscience Program, Syracuse University, Syracuse, NY 13244, USA
- BioInspired Institute, Syracuse University, Syracuse, NY 13244, USA
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14
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Buel GR, Chen X, Myint W, Kayode O, Folimonova V, Cruz A, Skorupka KA, Matsuo H, Walters KJ. E6AP AZUL interaction with UBQLN1/2 in cells, condensates, and an AlphaFold-NMR integrated structure. Structure 2023; 31:395-410.e6. [PMID: 36827983 PMCID: PMC10081965 DOI: 10.1016/j.str.2023.01.012] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2022] [Revised: 01/13/2023] [Accepted: 01/30/2023] [Indexed: 02/25/2023]
Abstract
The E3 ligase E6AP/UBE3A has a dedicated binding site in the 26S proteasome provided by the RAZUL domain of substrate receptor hRpn10/S5a/PSMD4. Guided by RAZUL sequence similarity, we test and demonstrate here that the E6AP AZUL binds transiently to the UBA of proteasomal shuttle factor UBQLN1/2. Despite a weak binding affinity, E6AP AZUL is recruited to UBQLN2 biomolecular condensates in vitro and E6AP interacts with UBQLN1/2 in cellulo. Steady-state and transfer nuclear Overhauser effect (NOE) experiments indicate direct interaction of AZUL with UBQLN1 UBA. Intermolecular contacts identified by NOE spectroscopy (NOESY) data were combined with AlphaFold2-Multimer predictions to yield an AZUL:UBA model structure. We additionally identify an oligomerization domain directly adjacent to UBQLN1/2 UBA (UBA adjacent [UBAA]) that is α-helical and allosterically reconfigured by AZUL binding to UBA. These data lead to a model of E6AP recruitment to UBQLN1/2 by AZUL:UBA interaction and provide fundamental information on binding requirements for interactions in condensates and cells.
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Affiliation(s)
- Gwen R Buel
- Protein Processing Section, Center for Structural Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Frederick, MD 21702, USA
| | - Xiang Chen
- Protein Processing Section, Center for Structural Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Frederick, MD 21702, USA
| | - Wazo Myint
- Cancer Innovation Laboratory, Frederick National Laboratory for Cancer Research, Frederick, MD 21702, USA
| | - Olumide Kayode
- Protein Processing Section, Center for Structural Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Frederick, MD 21702, USA
| | - Varvara Folimonova
- Protein Processing Section, Center for Structural Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Frederick, MD 21702, USA
| | - Anthony Cruz
- Protein Processing Section, Center for Structural Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Frederick, MD 21702, USA
| | - Katarzyna A Skorupka
- Cancer Innovation Laboratory, Frederick National Laboratory for Cancer Research, Frederick, MD 21702, USA
| | - Hiroshi Matsuo
- Cancer Innovation Laboratory, Frederick National Laboratory for Cancer Research, Frederick, MD 21702, USA
| | - Kylie J Walters
- Protein Processing Section, Center for Structural Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Frederick, MD 21702, USA.
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15
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Grønbæk-Thygesen M, Kampmeyer C, Hofmann K, Hartmann-Petersen R. The moonlighting of RAD23 in DNA repair and protein degradation. BIOCHIMICA ET BIOPHYSICA ACTA. GENE REGULATORY MECHANISMS 2023; 1866:194925. [PMID: 36863450 DOI: 10.1016/j.bbagrm.2023.194925] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2022] [Revised: 02/20/2023] [Accepted: 02/23/2023] [Indexed: 03/04/2023]
Abstract
A moonlighting protein is one, which carries out multiple, often wholly unrelated, functions. The RAD23 protein is a fascinating example of this, where the same polypeptide and the embedded domains function independently in both nucleotide excision repair (NER) and protein degradation via the ubiquitin-proteasome system (UPS). Hence, through direct binding to the central NER component XPC, RAD23 stabilizes XPC and contributes to DNA damage recognition. Conversely, RAD23 also interacts directly with the 26S proteasome and ubiquitylated substrates to mediate proteasomal substrate recognition. In this function, RAD23 activates the proteolytic activity of the proteasome and engages specifically in well-characterized degradation pathways through direct interactions with E3 ubiquitin-protein ligases and other UPS components. Here, we summarize the past 40 years of research into the roles of RAD23 in NER and the UPS.
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Affiliation(s)
- Martin Grønbæk-Thygesen
- The Linderstrøm-Lang Centre for Protein Science, Department of Biology, University of Copenhagen, Denmark.
| | - Caroline Kampmeyer
- The Linderstrøm-Lang Centre for Protein Science, Department of Biology, University of Copenhagen, Denmark
| | - Kay Hofmann
- Institute for Genetics, University of Cologne, Germany
| | - Rasmus Hartmann-Petersen
- The Linderstrøm-Lang Centre for Protein Science, Department of Biology, University of Copenhagen, Denmark.
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16
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Sato Y, Terawaki S, Oikawa D, Shimizu K, Okina Y, Ito H, Tokunaga F. Involvement of heterologous ubiquitination including linear ubiquitination in Alzheimer's disease and amyotrophic lateral sclerosis. Front Mol Biosci 2023; 10:1089213. [PMID: 36726375 PMCID: PMC9884707 DOI: 10.3389/fmolb.2023.1089213] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2022] [Accepted: 01/05/2023] [Indexed: 01/18/2023] Open
Abstract
In neurodegenerative diseases such as Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS), the progressive accumulation of ubiquitin-positive cytoplasmic inclusions leads to proteinopathy and neurodegeneration. Along with the seven types of Lys-linked ubiquitin chains, the linear ubiquitin chain assembly complex (LUBAC)-mediated Met1-linked linear ubiquitin chain, which activates the canonical NF-κB pathway, is also involved in cytoplasmic inclusions of tau in AD and TAR DNA-binding protein 43 in ALS. Post-translational modifications, including heterologous ubiquitination, affect proteasomal and autophagic degradation, inflammatory responses, and neurodegeneration. Single nucleotide polymorphisms (SNPs) in SHARPIN and RBCK1 (which encodes HOIL-1L), components of LUBAC, were recently identified as genetic risk factors of AD. A structural biological simulation suggested that most of the SHARPIN SNPs that cause an amino acid replacement affect the structure and function of SHARPIN. Thus, the aberrant LUBAC activity is related to AD. Protein ubiquitination and ubiquitin-binding proteins, such as ubiquilin 2 and NEMO, facilitate liquid-liquid phase separation (LLPS), and linear ubiquitination seems to promote efficient LLPS. Therefore, the development of therapeutic approaches that target ubiquitination, such as proteolysis-targeting chimeras (PROTACs) and inhibitors of ubiquitin ligases, including LUBAC, is expected to be an additional effective strategy to treat neurodegenerative diseases.
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Affiliation(s)
- Yusuke Sato
- Center for Research on Green Sustainable Chemistry, Graduate School of Engineering, Tottori University, Tottori, Japan,Department of Chemistry and Biotechnology, Graduate School of Engineering, Tottori University, Tottori, Japan
| | - Seigo Terawaki
- Department of Medical Biochemistry, Graduate School of Medicine, Osaka Metropolitan University, Osaka, Japan,Department of Molecular and Genetic Medicine, Kawasaki Medical School, Kurashiki, Japan
| | - Daisuke Oikawa
- Department of Medical Biochemistry, Graduate School of Medicine, Osaka Metropolitan University, Osaka, Japan
| | - Kouhei Shimizu
- Department of Medical Biochemistry, Graduate School of Medicine, Osaka Metropolitan University, Osaka, Japan
| | - Yoshinori Okina
- Department of Medical Biochemistry, Graduate School of Medicine, Osaka Metropolitan University, Osaka, Japan
| | - Hidefumi Ito
- Department of Neurology, Wakayama Medical University, Wakayama, Japan
| | - Fuminori Tokunaga
- Department of Medical Biochemistry, Graduate School of Medicine, Osaka Metropolitan University, Osaka, Japan,*Correspondence: Fuminori Tokunaga,
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17
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Mohanty P, Kapoor U, Sundaravadivelu Devarajan D, Phan TM, Rizuan A, Mittal J. Principles Governing the Phase Separation of Multidomain Proteins. Biochemistry 2022; 61:2443-2455. [PMID: 35802394 PMCID: PMC9669140 DOI: 10.1021/acs.biochem.2c00210] [Citation(s) in RCA: 37] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
A variety of membraneless organelles, often termed "biological condensates", play an important role in the regulation of cellular processes such as gene transcription, translation, and protein quality control. On the basis of experimental and theoretical investigations, liquid-liquid phase separation (LLPS) has been proposed as a possible mechanism for the origin of biological condensates. LLPS requires multivalent macromolecules that template the formation of long-range, intermolecular interaction networks and results in the formation of condensates with defined composition and material properties. Multivalent interactions driving LLPS exhibit a wide range of modes from highly stereospecific to nonspecific and involve both folded and disordered regions. Multidomain proteins serve as suitable macromolecules for promoting phase separation and achieving disparate functions due to their potential for multivalent interactions and regulation. Here, we aim to highlight the influence of the domain architecture and interdomain interactions on the phase separation of multidomain protein condensates. First, the general principles underlying these interactions are illustrated on the basis of examples of multidomain proteins that are predominantly associated with nucleic acid binding and protein quality control and contain both folded and disordered regions. Next, the examples showcase how LLPS properties of folded and disordered regions can be leveraged to engineer multidomain constructs that form condensates with the desired assembly and functional properties. Finally, we highlight the need for improvements in coarse-grained computational models that can provide molecular-level insights into multidomain protein condensates in conjunction with experimental efforts.
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Affiliation(s)
- Priyesh Mohanty
- Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX 77843
| | - Utkarsh Kapoor
- Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX 77843
| | | | - Tien Minh Phan
- Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX 77843
| | - Azamat Rizuan
- Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX 77843
| | - Jeetain Mittal
- Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, TX 77843
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18
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Lin BC, Higgins NR, Phung TH, Monteiro MJ. UBQLN proteins in health and disease with a focus on UBQLN2 in ALS/FTD. FEBS J 2022; 289:6132-6153. [PMID: 34273246 PMCID: PMC8761781 DOI: 10.1111/febs.16129] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Revised: 07/08/2021] [Accepted: 07/16/2021] [Indexed: 01/12/2023]
Abstract
Ubiquilin (UBQLN) proteins are a dynamic and versatile family of proteins found in all eukaryotes that function in the regulation of proteostasis. Besides their canonical function as shuttle factors in delivering misfolded proteins to the proteasome and autophagy systems for degradation, there is emerging evidence that UBQLN proteins play broader roles in proteostasis. New information suggests the proteins function as chaperones in protein folding, protecting proteins prior to membrane insertion, and as guardians for mitochondrial protein import. In this review, we describe the evidence for these different roles, highlighting how different domains of the proteins impart these functions. We also describe how changes in the structure and phase separation properties of UBQLNs may regulate their activity and function. Finally, we discuss the pathogenic mechanisms by which mutations in UBQLN2 cause amyotrophic lateral sclerosis and frontotemporal dementia. We describe the animal model systems made for different UBQLN2 mutations and how lessons learnt from these systems provide fundamental insight into the molecular mechanisms by which UBQLN2 mutations drive disease pathogenesis through disturbances in proteostasis.
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Affiliation(s)
- Brian C. Lin
- Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD, USA,Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, MD, USA,Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Nicole R. Higgins
- Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, MD, USA,Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, MD, USA,Program in Molecular Medicine, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Trong H. Phung
- Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, MD, USA,Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, MD, USA
| | - Mervyn J. Monteiro
- Program in Neuroscience, University of Maryland School of Medicine, Baltimore, MD, USA,Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, MD, USA,Department of Anatomy and Neurobiology, University of Maryland School of Medicine, Baltimore, MD, USA,Program in Molecular Medicine, University of Maryland School of Medicine, Baltimore, MD, USA
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19
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Li Z, Liu X, Liu M. Stress Granule Homeostasis, Aberrant Phase Transition, and Amyotrophic Lateral Sclerosis. ACS Chem Neurosci 2022; 13:2356-2370. [PMID: 35905138 DOI: 10.1021/acschemneuro.2c00262] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease. In recent years, a large number of ALS-related mutations have been discovered to have a strong link to stress granules (SGs). SGs are cytoplasmic ribonucleoprotein condensates mediated by liquid-liquid phase separation (LLPS) of biomacromolecules. They help cells cope with stress. The normal physiological functions of SGs are dependent on three key aspects of SG "homeostasis": SG assembly, disassembly, and SG components. Any of these three aspects can be disrupted, resulting in abnormalities in the cellular stress response and leading to cytotoxicity. Several ALS-related pathogenic mutants have abnormal LLPS abilities that disrupt SG homeostasis, and some of them can even cause aberrant phase transitions. As a result, ALS-related mutants may disrupt various aspects of SG homeostasis by directly disturbing the intermolecular interactions or affecting core SG components, thus disrupting the phase equilibrium of the cytoplasm during stress. Considering that the importance of the "global view" of SG homeostasis in ALS pathogenesis has not received enough attention, we first systematically summarize the physiological regulatory mechanism of SG homeostasis based on LLPS and then examine ALS pathogenesis from the perspective of disrupted SG homeostasis and aberrant phase transition of biomacromolecules.
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Affiliation(s)
- Zhanxu Li
- Xiangya School of Medicine, Central South University, Changsha 410078, Hunan, China
| | - Xionghao Liu
- Center for Medical Genetics & Hunan Key Laboratory of Medical Genetics, School of Life Sciences, Central South University, Changsha 410008, Hunan, China
| | - Mujun Liu
- Department of Cell Biology, School of Life Sciences, Central South University, Changsha 410078, Hunan, China
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20
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Mohan HM, Trzeciakiewicz H, Pithadia A, Crowley EV, Pacitto R, Safren N, Trotter B, Zhang C, Zhou X, Zhang Y, Basrur V, Paulson HL, Sharkey LM. RTL8 promotes nuclear localization of UBQLN2 to subnuclear compartments associated with protein quality control. Cell Mol Life Sci 2022; 79:176. [PMID: 35247097 PMCID: PMC9376861 DOI: 10.1007/s00018-022-04170-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Revised: 01/17/2022] [Accepted: 01/25/2022] [Indexed: 11/24/2022]
Abstract
The brain-expressed ubiquilins (UBQLNs) 1, 2 and 4 are a family of ubiquitin adaptor proteins that participate broadly in protein quality control (PQC) pathways, including the ubiquitin proteasome system (UPS). One family member, UBQLN2, has been implicated in numerous neurodegenerative diseases including ALS/FTD. UBQLN2 typically resides in the cytoplasm but in disease can translocate to the nucleus, as in Huntington's disease where it promotes the clearance of mutant Huntingtin. How UBQLN2 translocates to the nucleus and clears aberrant nuclear proteins, however, is not well understood. In a mass spectrometry screen to discover UBQLN2 interactors, we identified a family of small (13 kDa), highly homologous uncharacterized proteins, RTL8, and confirmed the interaction between UBQLN2 and RTL8 both in vitro using recombinant proteins and in vivo using mouse brain tissue. Under endogenous and overexpressed conditions, RTL8 localizes to nucleoli. When co-expressed with UBQLN2, RTL8 promotes nuclear translocation of UBQLN2. RTL8 also facilitates UBQLN2's nuclear translocation during heat shock. UBQLN2 and RTL8 colocalize within ubiquitin-enriched subnuclear structures containing PQC components. The robust effect of RTL8 on the nuclear translocation and subnuclear localization of UBQLN2 does not extend to the other brain-expressed ubiquilins, UBQLN1 and UBQLN4. Moreover, compared to UBQLN1 and UBQLN4, UBQLN2 preferentially stabilizes RTL8 levels in human cell lines and in mouse brain, supporting functional heterogeneity among UBQLNs. As a novel UBQLN2 interactor that recruits UBQLN2 to specific nuclear compartments, RTL8 may regulate UBQLN2 function in nuclear protein quality control.
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Affiliation(s)
- Harihar Milaganur Mohan
- Department of Neurology, University of Michigan, Ann Arbor, MI, 48109-2200, USA.,Graduate Program in Cellular and Molecular Biology, University of Michigan, Ann Arbor, MI, 48109-2200, USA
| | | | - Amit Pithadia
- Department of Neurology, University of Michigan, Ann Arbor, MI, 48109-2200, USA
| | - Emily V Crowley
- Department of Neurology, University of Michigan, Ann Arbor, MI, 48109-2200, USA
| | - Regina Pacitto
- Department of Neurology, University of Michigan, Ann Arbor, MI, 48109-2200, USA
| | - Nathaniel Safren
- Department of Neurology, University of Michigan, Ann Arbor, MI, 48109-2200, USA.,Department of Neurology, Northwestern University Feinberg School of Medicine, Chicago, IL, 60611, USA
| | - Bryce Trotter
- Department of Neurology, University of Michigan, Ann Arbor, MI, 48109-2200, USA
| | - Chengxin Zhang
- Department of Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, MI, 48109-2200, USA
| | - Xiaogen Zhou
- Department of Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, MI, 48109-2200, USA
| | - Yang Zhang
- Department of Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, MI, 48109-2200, USA
| | - Venkatesha Basrur
- Department of Pathology, University of Michigan Medical School, Ann Arbor, MI, 48109, USA
| | - Henry L Paulson
- Department of Neurology, University of Michigan, Ann Arbor, MI, 48109-2200, USA. .,Michigan Neuroscience Institute, University of Michigan, Ann Arbor, MI, 48109-2200, USA.
| | - Lisa M Sharkey
- Department of Neurology, University of Michigan, Ann Arbor, MI, 48109-2200, USA. .,Michigan Neuroscience Institute, University of Michigan, Ann Arbor, MI, 48109-2200, USA.
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21
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Taneja I, Holehouse AS. Folded domain charge properties influence the conformational behavior of disordered tails. Curr Res Struct Biol 2021; 3:216-228. [PMID: 34557680 PMCID: PMC8446786 DOI: 10.1016/j.crstbi.2021.08.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2021] [Accepted: 08/26/2021] [Indexed: 12/22/2022] Open
Abstract
Intrinsically disordered proteins and protein regions (IDRs) make up around 30% of the human proteome where they play essential roles in dictating and regulating many core biological processes. While IDRs are often studied as isolated domains, in naturally occurring proteins most IDRs are found adjacent to folded domains, where they exist as either N- or C-terminal tails or as linkers connecting two folded domains. Prior work has shown that charge properties of IDRs can influence their conformational behavior, both in isolation and in the context of folded domains. In contrast, the converse scenario is less well-explored: how do the charge properties of folded domains influence IDR conformational behavior? To answer this question, we combined a large-scale structural bioinformatics analysis with all-atom implicit solvent simulations of both rationally designed and naturally occurring proteins. Our results reveal three key takeaways. Firstly, the relative position and accessibility of charged residues across the surface of a folded domain can dictate IDR conformational behavior, overriding expectations based on net surface charge properties. Secondly, naturally occurring proteins possess multiple charge patches that are physically accessible to local IDRs. Finally, even modest changes in the local electrostatic environment of a folded domain can substantially modulate IDR-folded domain interactions. Taken together, our results suggest that folded domain surfaces can act as local determinants of IDR conformational behavior. Intrinsically disordered regions (IDRs) are mostly found adjacent to folded domains. Here we propose that the folded domain surface properties influence IDR behavior. We combine all-atom simulations and sequence design of IDRs and folded domains. IDR conformational behavior is determined by a complex combination of factors. Folded domains can substantially alter IDR conformational biases.
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Affiliation(s)
- Ishan Taneja
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO, 63110, USA.,Center for Science and Engineering of Living Systems (CSELS), Washington University in St. Louis, St. Louis, MO, 63130, USA
| | - Alex S Holehouse
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO, 63110, USA.,Center for Science and Engineering of Living Systems (CSELS), Washington University in St. Louis, St. Louis, MO, 63130, USA
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22
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Zheng T, Galagedera SKK, Castañeda CA. Previously uncharacterized interactions between the folded and intrinsically disordered domains impart asymmetric effects on UBQLN2 phase separation. Protein Sci 2021; 30:1467-1481. [PMID: 34029402 DOI: 10.1002/pro.4128] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2021] [Revised: 05/20/2021] [Accepted: 05/21/2021] [Indexed: 02/06/2023]
Abstract
Shuttle protein UBQLN2 functions in protein quality control (PQC) by binding to proteasomal receptors and ubiquitinated substrates via its N-terminal ubiquitin-like (UBL) and C-terminal ubiquitin-associated (UBA) domains, respectively. Between these two folded domains are low-complexity STI1-I and STI1-II regions, connected by disordered linkers. The STI1 regions bind other components, such as HSP70, that are important to the PQC functions of UBQLN2. We recently determined that the STI1-II region enables UBQLN2 to undergo liquid-liquid phase separation (LLPS) to form liquid droplets in vitro and biomolecular condensates in cells. However, how the interplay between the folded (UBL/UBA) domains and the intrinsically disordered regions mediates phase separation is largely unknown. Using engineered domain deletion constructs, we found that removing the UBA domain inhibits UBQLN2 LLPS while removing the UBL domain enhances LLPS, suggesting that UBA and UBL domains contribute asymmetrically in modulating UBQLN2 LLPS. To explain these differential effects, we interrogated the interactions that involve the UBA and UBL domains across the entire UBQLN2 molecule using nuclear magnetic resonance spectroscopy. To our surprise, aside from well-studied canonical UBL:UBA interactions, there also exist moderate interactions between the UBL and several disordered regions, including STI1-I and residues 555-570, the latter of which is a known contributor to UBQLN2 LLPS. Our findings are essential for the understanding of both the molecular driving forces of UBQLN2 LLPS and the effects of ligand binding to UBL, UBA, or disordered regions on the phase behavior and physiological functions of UBQLN2.
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Affiliation(s)
- Tongyin Zheng
- Department of Chemistry, Syracuse University, Syracuse, New York, USA
| | | | - Carlos A Castañeda
- Departments of Biology and Chemistry, Syracuse University, Syracuse, New York, USA.,Interdisciplinary Neuroscience Program, Syracuse University, Syracuse, New York, USA.,BioInspired Institute, Syracuse University, Syracuse, New York, USA
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