1
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Haller SL, Park C, Bruneau RC, Megawati D, Zhang C, Vipat S, Peng C, Senkevich TG, Brennan G, Tazi L, Rothenburg S. Molecular basis for the host range function of the poxvirus PKR inhibitor E3. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.05.16.594589. [PMID: 38798513 PMCID: PMC11118487 DOI: 10.1101/2024.05.16.594589] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2024]
Abstract
The antiviral protein kinase R (PKR) is activated by viral double-stranded RNA and phosphorylates translation initiation factor eIF2α, thereby inhibiting translation and virus replication. Most poxviruses contain two PKR inhibitors, called E3 and K3 in vaccinia virus (VACV), which are determinants of viral host range. The prevailing model for E3 function is that it inhibits PKR through the non-specific sequestration of double-stranded (ds) RNA. Our data revealed that Syrian hamster PKR was resistant to E3, which is at odds with the sequestration model. However, Syrian hamster PKR was still sensitive to K3 inhibition. In contrast, Armenian hamster PKR showed opposite sensitivities, being sensitive to E3 and resistant to K3 inhibition. Mutational analyses of hamster PKRs showed that sensitivity to E3 inhibition was largely determined by the region linking the dsRNA-binding domains and the kinase domain of PKR, whereas two amino acid residues in the kinase domain (helix αG) determined sensitivity to K3. Expression of PKRs in congenic cells showed that Syrian hamster PKR containing the two Armenian hamster PKR residues in helix-αG was resistant to wild type VACV infection, and that cells expressing either hamster PKR recapitulated the phenotypes observed in species-derived cell lines. The observed resistance of Syrian hamster PKR to E3 explains its host range function and challenges the paradigm that dsRNA-binding PKR inhibitors mainly act by the sequestration of dsRNA. Significance The molecular mechanisms that govern the host range of viruses are incompletely understood. A small number of poxvirus genes have been identified that influence the host range of poxviruses. We show that the host range functions of E3 and K3, two host range factors from vaccinia virus, are a result of species-specific interactions with the antiviral protein kinase R (PKR) and that PKR from closely related species displayed dramatic differences in their sensitivities to these viral inhibitors. While there is a substantial body of work demonstrating host-specific interactions with K3, the current model for E3-mediated PKR inhibition is that E3 non-specifically sequesters dsRNA to prevent PKR activation. This model does not predict species-specific sensitivity to E3; therefore, our data suggest that the current model is incomplete, and that dsRNA sequestration is not the primary mechanism for E3 activity.
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2
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Zhang R, Karijolich J. RNA recognition by PKR during DNA virus infection. J Med Virol 2024; 96:e29424. [PMID: 38285432 PMCID: PMC10832991 DOI: 10.1002/jmv.29424] [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: 12/03/2023] [Revised: 01/10/2024] [Accepted: 01/11/2024] [Indexed: 01/30/2024]
Abstract
Protein kinase R (PKR) is a double-stranded RNA (dsRNA) binding protein that plays a crucial role in innate immunity during viral infection and can restrict both DNA and RNA viruses. The potency of its antiviral function is further reflected by the large number of viral-encoded PKR antagonists. However, much about the regulation of dsRNA accumulation and PKR activation during viral infection remains unknown. Since DNA viruses do not have an RNA genome or RNA replication intermediates like RNA viruses do, PKR-mediated dsRNA detection in the context of DNA virus infection is particularly intriguing. Here, we review the current state of knowledge regarding the regulation of PKR activation and its antagonism during infection with DNA viruses.
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Affiliation(s)
- Ruilin Zhang
- Department of Pathology, Microbiology, and Immunology, Vanderbilt University School of Medicine, Nashville, TN 37232-2363, USA
- Vanderbilt Institute for Infection, Immunology and Inflammation, Vanderbilt Center for Immunobiology, Nashville. Nashville, TN 37232-2363, USA
| | - John Karijolich
- Department of Pathology, Microbiology, and Immunology, Vanderbilt University School of Medicine, Nashville, TN 37232-2363, USA
- Vanderbilt Institute for Infection, Immunology and Inflammation, Vanderbilt Center for Immunobiology, Nashville. Nashville, TN 37232-2363, USA
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3
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Chaumont L, Collet B, Boudinot P. Protein kinase double-stranded RNA-dependent (PKR) in antiviral defence in fish and mammals. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2023; 145:104732. [PMID: 37172664 DOI: 10.1016/j.dci.2023.104732] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2023] [Revised: 05/07/2023] [Accepted: 05/09/2023] [Indexed: 05/15/2023]
Abstract
The interferon-inducible double-stranded RNA-dependent protein kinase (PKR) is one of the key antiviral arms of the innate immune system. Upon binding of viral double stranded RNA, a viral Pattern Associated Molecular Pattern (PAMP), PKR gets activated and phosphorylates the eukaryotic initiation factor 2α (eIF2α) resulting in a protein shut-down that limits viral replication. Since its discovery in the mid-seventies, PKR has been shown to be involved in multiple important cellular processes including apoptosis, proinflammatory and innate immune responses. Viral subversion mechanisms of PKR underline its importance in the antiviral response of the host. PKR activation pathways and its mechanisms of action were previously identified and characterised mostly in mammalian models. However, fish Pkr and fish-specific paralogue Z-DNA-dependent protein kinase (Pkz) also play key role in antiviral defence. This review gives an update on the current knowledge on fish Pkr/Pkz, their conditions of activation and their implication in the immune responses to viruses, in comparison to their mammalian counterparts.
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Affiliation(s)
- Lise Chaumont
- Université Paris-Saclay, INRAE, UVSQ, VIM, Jouy-en-Josas, 78350, France
| | - Bertrand Collet
- Université Paris-Saclay, INRAE, UVSQ, VIM, Jouy-en-Josas, 78350, France
| | - Pierre Boudinot
- Université Paris-Saclay, INRAE, UVSQ, VIM, Jouy-en-Josas, 78350, France.
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4
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Strofaldi A, Quinn MK, Seddon AM, McManus JJ. Polymorphic protein phase transitions driven by surface anisotropy. J Chem Phys 2023; 158:014905. [PMID: 36610968 DOI: 10.1063/5.0125452] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Phase transitions of proteins are strongly influenced by surface chemical modifications or mutations. Human γD-crystallin (HGD) single-mutants have been extensively studied because they are associated with the onset of juvenile cataract. However, they have also provided a rich library of molecules to examine how specific inter-protein interactions direct protein assembly, providing new insights and valuable experimental data for coarse-grained patchy-particle models. Here, we demonstrate that the addition of new inter-protein interactions by mutagenesis is additive and increases the number and variety of condensed phases formed by proteins. When double mutations incorporating two specific single point mutations are made, the properties of both single mutations are retained in addition to the formation of a new condensed phase. We find that the HGD double-mutant P23VC110M self-assembles into spherical particles with retrograde solubility, orthorhombic crystals, and needle/plate shape crystals, while retaining the ability to undergo liquid-liquid phase separation. This rich polymorphism is only partially predicted by the experimental data on the constituent single mutants. We also report a previously un-characterized amorphous protein particle, with unique properties that differ from those of protein spherulites, protein particulates previously described. The particles we observe are amorphous, reversible with temperature, tens of microns in size, and perfectly spherical. When they are grown on pristine surfaces, they appear to form by homogeneous nucleation, making them unique, and we believe a new form of protein condensate. This work highlights the challenges in predicting protein behavior, which has frustrated rational assembly and crystallization but also provides rich data to develop new coarse-grained models to explain the observed polymorphism.
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Affiliation(s)
| | - Michelle K Quinn
- Department of Chemistry Maynooth University, Maynooth, Co. Kildare, Ireland
| | - Annela M Seddon
- HH Wills Physics Laboratory, School of Physics, University of Bristol, Bristol BS8 1TL, United Kingdom
| | - Jennifer J McManus
- HH Wills Physics Laboratory, School of Physics, University of Bristol, Bristol BS8 1TL, United Kingdom
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5
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Hesler S, Angeliadis M, Husain B, Cole JL. Contribution of dsRBD2 to PKR Activation. ACS OMEGA 2021; 6:11367-11374. [PMID: 34056292 PMCID: PMC8153938 DOI: 10.1021/acsomega.1c00343] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/19/2021] [Accepted: 04/02/2021] [Indexed: 06/12/2023]
Abstract
Protein kinase R (PKR) is a key pattern recognition receptor of the innate immune pathway. PKR is activated by double-stranded RNA (dsRNA) that is often produced during viral genome replication and transcription. PKR contains two tandem double-stranded RNA binding domains at the N-terminus, dsRBD1 and dsRBD2, and a C-terminal kinase domain. In the canonical model for activation, RNAs that bind multiple PKRs induce dimerization of the kinase domain that promotes an active conformation. However, there is evidence that dimerization of the kinase domain is not sufficient to mediate activation and PKR activation is modulated by the RNA-binding mode. dsRBD2 lacks most of the consensus RNA-binding residues, and it has been suggested to function as a modulator of PKR activation. Here, we demonstrate that dsRBD2 regulates PKR activation and identify the N-terminal helix as a critical region for modulating kinase activity. Mutations in dsRBD2 that have minor effects on overall dsRNA-binding affinity strongly inhibit the activation of PKR by dsRNA. These mutations also inhibit RNA-independent PKR activation. These data support a model where dsRBD2 has evolved to function as a regulator of the kinase.
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Affiliation(s)
- Stephen Hesler
- Department
of Molecular and Cell Biology, University
of Connecticut, Storrs 06269, Connecticut, United States
| | - Matthew Angeliadis
- Department
of Molecular and Cell Biology, University
of Connecticut, Storrs 06269, Connecticut, United States
| | - Bushra Husain
- Department
of Molecular and Cell Biology, University
of Connecticut, Storrs 06269, Connecticut, United States
| | - James L. Cole
- Department
of Molecular and Cell Biology, University
of Connecticut, Storrs 06269, Connecticut, United States
- Department
of Chemistry, University of Connecticut, Storrs 06269, Connecticut, United States
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6
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Analytical ultracentrifuge: an ideal tool for characterization of non-coding RNAs. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2020; 49:809-818. [PMID: 33067686 DOI: 10.1007/s00249-020-01470-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2020] [Revised: 09/26/2020] [Accepted: 10/05/2020] [Indexed: 12/25/2022]
Abstract
Analytical ultracentrifugation (AUC) has emerged as a robust and reliable technique for biomolecular characterization with extraordinary sensitivity. AUC is widely used to study purity, conformational changes, biomolecular interactions, and stoichiometry. Furthermore, AUC is used to determine the molecular weight of biomolecules such as proteins, carbohydrates, and DNA and RNA. Due to the multifaceted role(s) of non-coding RNAs from viruses, prokaryotes, and eukaryotes, research aimed at understanding the structure-function relationships of non-coding RNAs is rapidly increasing. However, due to their large size, flexibility, complicated secondary structures, and conformations, structural studies of non-coding RNAs are challenging. In this review, we are summarizing the application of AUC to evaluate the homogeneity, interactions, and conformational changes of non-coding RNAs from adenovirus as well as from Murray Valley, Powassan, and West Nile viruses. We also discuss the application of AUC to characterize eukaryotic long non-coding RNAs, Xist, and HOTAIR. These examples highlight the significant role AUC can play in facilitating the structural determination of non-coding RNAs and their complexes.
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7
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Bou-Nader C, Gordon JM, Henderson FE, Zhang J. The search for a PKR code-differential regulation of protein kinase R activity by diverse RNA and protein regulators. RNA (NEW YORK, N.Y.) 2019; 25:539-556. [PMID: 30770398 PMCID: PMC6467004 DOI: 10.1261/rna.070169.118] [Citation(s) in RCA: 41] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
The interferon-inducible protein kinase R (PKR) is a key component of host innate immunity that restricts viral replication and propagation. As one of the four eIF2α kinases that sense diverse stresses and direct the integrated stress response (ISR) crucial for cell survival and proliferation, PKR's versatile roles extend well beyond antiviral defense. Targeted by numerous host and viral regulators made of RNA and proteins, PKR is subject to multiple layers of endogenous control and external manipulation, driving its rapid evolution. These versatile regulators include not only the canonical double-stranded RNA (dsRNA) that activates the kinase activity of PKR, but also highly structured viral, host, and artificial RNAs that exert a full spectrum of effects. In this review, we discuss our deepening understanding of the allosteric mechanism that connects the regulatory and effector domains of PKR, with an emphasis on diverse structured RNA regulators in comparison to their protein counterparts. Through this analysis, we conclude that much of the mechanistic details that underlie this RNA-regulated kinase await structural and functional elucidation, upon which we can then describe a "PKR code," a set of structural and chemical features of RNA that are both descriptive and predictive for their effects on PKR.
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Affiliation(s)
- Charles Bou-Nader
- Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892, USA
| | - Jackson M Gordon
- Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892, USA
| | - Frances E Henderson
- Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892, USA
| | - Jinwei Zhang
- Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892, USA
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8
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Dzananovic E, McKenna SA, Patel TR. Viral proteins targeting host protein kinase R to evade an innate immune response: a mini review. Biotechnol Genet Eng Rev 2018; 34:33-59. [PMID: 29716441 DOI: 10.1080/02648725.2018.1467151] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The innate immune system offers a first line of defense by neutralizing foreign pathogens such as bacteria, fungi, and viruses. These pathogens express molecules (RNA and proteins) that have discrete structures, known as the pathogen-associated molecular patterns that are recognized by a highly specialized class of host proteins called pattern recognition receptors to facilitate the host's immune response against infection. The RNA-dependent Protein Kinase R (PKR) is one of the host's pattern recognition receptors that is a key component of an innate immune system. PKR recognizes imperfectly double-stranded non-coding viral RNA molecules via its N-terminal double-stranded RNA binding motifs, undergoes phosphorylation of the C-terminal kinase domain, ultimately resulting in inhibition of viral protein translation by inhibiting the guanine nucleotide exchange activity of eukaryotic initiation factor 2α. Not surprisingly, viruses have evolved mechanisms by which viral non-coding RNA or protein molecules inhibit PKR's activation and/or its downstream activity to allow viral replication. In this review, we will highlight the role of viral proteins in inhibiting PKR's activity and summarize currently known mechanisms by which viral proteins execute such inhibitory activity.
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Affiliation(s)
- Edis Dzananovic
- a Plant Pathology, Plant Protection and Molecular Biology , Agriculture and Agri-Food Canada , Saskatoon , Canada
| | - Sean A McKenna
- b Department of Chemistry, Manitoba Institute for Materials, Department of Biochemistry and Medical Genetics , University of Manitoba , Winnipeg , Canada
| | - Trushar R Patel
- c Department of Chemistry and Biochemistry , Alberta RNA Research and Training Institute, University of Lethbridge , Lethbridge , Canada.,d DiscoveryLab, Faculty of Medicine & Dentistry , University of Alberta , Edmonton , Canada.,e Department of Microbiology, Immunology and Infectious Diseases, Cumming School of Medicine , University of Calgary , Calgary , Canada
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9
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Impact of the structural integrity of the three-way junction of adenovirus VAI RNA on PKR inhibition. PLoS One 2017; 12:e0186849. [PMID: 29053745 PMCID: PMC5650172 DOI: 10.1371/journal.pone.0186849] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2017] [Accepted: 10/09/2017] [Indexed: 02/06/2023] Open
Abstract
Highly structured RNA derived from viral genomes is a key cellular indicator of viral infection. In response, cells produce the interferon inducible RNA-dependent protein kinase (PKR) that, when bound to viral dsRNA, phosphorylates eukaryotic initiation factor 2α and attenuates viral protein translation. Adenovirus can evade this line of defence through transcription of a non-coding RNA, VAI, an inhibitor of PKR. VAI consists of three base-paired regions that meet at a three-way junction; an apical stem responsible for the interaction with PKR, a central stem required for inhibition, and a terminal stem. Recent studies have highlighted the potential importance of the tertiary structure of the three-way junction to PKR inhibition by enabling interaction between regions of the central and terminal stems. To further investigate the role of the three-way junction, we characterized the binding affinity and inhibitory potential of central stem mutants designed to introduce subtle alterations. These results were then correlated with small-angle X-ray scattering solution studies and computational tertiary structural models. Our results demonstrate that while mutations to the central stem have no observable effect on binding affinity to PKR, mutations that appear to disrupt the structure of the three-way junction prevent inhibition of PKR. Therefore, we propose that instead of simply sequestering PKR, a specific structural conformation of the PKR-VAI complex may be required for inhibition.
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10
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Abstract
Although the antiviral kinase PKR was originally characterized as a double-stranded RNA activated enzyme it can be stimulated by RNAs containing limited secondary structure. Single-stranded regions in such RNAs contribute to binding and activation but the mechanism is not understood. Here, we demonstrate that single-stranded RNAs bind to PKR with micromolar dissociation constants and can induce activation. Addition of a 5'-triphosphate slightly enhances binding affinity. Single-stranded RNAs also activate PKR constructs lacking the double-stranded RNA binding domain and bind to a basic region adjacent to the N-terminus of the kinase. However, the isolated kinase is not activated by and does not bind single-stranded RNA. Photocrosslinking measurements demonstrate that that the basic region interacts with RNA in the context of full length PKR. We propose that bivalent interactions with the double stranded RNA binding domain and the basic region underlie the ability of RNAs containing limited structure to activate PKR by enhancing binding affinity and thereby increasing the population of productive complexes containing two PKRs bound to a single RNA.
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11
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Structural studies of RNA-protein complexes: A hybrid approach involving hydrodynamics, scattering, and computational methods. Methods 2016; 118-119:146-162. [PMID: 27939506 DOI: 10.1016/j.ymeth.2016.12.002] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2016] [Revised: 12/01/2016] [Accepted: 12/05/2016] [Indexed: 01/01/2023] Open
Abstract
The diverse functional cellular roles played by ribonucleic acids (RNA) have emphasized the need to develop rapid and accurate methodologies to elucidate the relationship between the structure and function of RNA. Structural biology tools such as X-ray crystallography and Nuclear Magnetic Resonance are highly useful methods to obtain atomic-level resolution models of macromolecules. However, both methods have sample, time, and technical limitations that prevent their application to a number of macromolecules of interest. An emerging alternative to high-resolution structural techniques is to employ a hybrid approach that combines low-resolution shape information about macromolecules and their complexes from experimental hydrodynamic (e.g. analytical ultracentrifugation) and solution scattering measurements (e.g., solution X-ray or neutron scattering), with computational modeling to obtain atomic-level models. While promising, scattering methods rely on aggregation-free, monodispersed preparations and therefore the careful development of a quality control pipeline is fundamental to an unbiased and reliable structural determination. This review article describes hydrodynamic techniques that are highly valuable for homogeneity studies, scattering techniques useful to study the low-resolution shape, and strategies for computational modeling to obtain high-resolution 3D structural models of RNAs, proteins, and RNA-protein complexes.
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12
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DeForte S, Uversky VN. Order, Disorder, and Everything in Between. Molecules 2016; 21:molecules21081090. [PMID: 27548131 PMCID: PMC6274243 DOI: 10.3390/molecules21081090] [Citation(s) in RCA: 64] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2016] [Revised: 08/10/2016] [Accepted: 08/11/2016] [Indexed: 02/04/2023] Open
Abstract
In addition to the “traditional” proteins characterized by the unique crystal-like structures needed for unique functions, it is increasingly recognized that many proteins or protein regions (collectively known as intrinsically disordered proteins (IDPs) and intrinsically disordered protein regions (IDPRs)), being biologically active, do not have a specific 3D-structure in their unbound states under physiological conditions. There are also subtler categories of disorder, such as conditional (or dormant) disorder and partial disorder. Both the ability of a protein/region to fold into a well-ordered functional unit or to stay intrinsically disordered but functional are encoded in the amino acid sequence. Structurally, IDPs/IDPRs are characterized by high spatiotemporal heterogeneity and exist as dynamic structural ensembles. It is important to remember, however, that although structure and disorder are often treated as binary states, they actually sit on a structural continuum.
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Affiliation(s)
- Shelly DeForte
- Department of Molecular Medicine, Morsani College of Medicine, University of South Florida, Tampa, FL 33612, USA.
| | - Vladimir N Uversky
- Department of Molecular Medicine, Morsani College of Medicine, University of South Florida, Tampa, FL 33612, USA.
- USF Health Byrd Alzheimer's Research Institute, Morsani College of Medicine, University of South Florida, Tampa, FL 33612, USA.
- Laboratory of Structural Dynamics, Stability and Folding of Proteins, Institute of Cytology, Russian Academy of Sciences, St. Petersburg 194064, Russia.
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13
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Mayo CB, Wong CJ, Lopez PE, Lary JW, Cole JL. Activation of PKR by short stem-loop RNAs containing single-stranded arms. RNA (NEW YORK, N.Y.) 2016; 22:1065-75. [PMID: 27208315 PMCID: PMC4911914 DOI: 10.1261/rna.053348.115] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2015] [Accepted: 04/19/2016] [Indexed: 05/22/2023]
Abstract
Protein kinase R (PKR) is a central component of the innate immunity antiviral pathway and is activated by dsRNA. PKR contains a C-terminal kinase domain and two tandem dsRNA binding domains. In the canonical activation model, binding of multiple PKR monomers to dsRNA enhances dimerization of the kinase domain, leading to enzymatic activation. A minimal dsRNA of 30 bp is required for activation. However, short (∼15 bp) stem-loop RNAs containing flanking single-stranded tails (ss-dsRNAs) are capable of activating PKR. Activation was reported to require a 5'-triphosphate. Here, we characterize the structural features of ss-dsRNAs that contribute to activation. We have designed a model ss-dsRNA containing 15-nt single-stranded tails and a 15-bp stem and made systematic truncations of the tail and stem regions. Autophosphorylation assays and analytical ultracentrifugation experiments were used to correlate activation and binding affinity. PKR activation requires both 5'- and 3'-single-stranded tails but the triphosphate is dispensable. Activation potency and binding affinity decrease as the ssRNA tails are truncated and activation is abolished in cases where the binding affinity is strongly reduced. These results indicate that the single-stranded regions bind to PKR and support a model where ss-dsRNA induced dimerization is required but not sufficient to activate the kinase. The length of the duplex regions in several natural RNA activators of PKR is below the minimum of 30 bp required for activation and similar interactions with single-stranded regions may contribute to PKR activation in these cases.
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Affiliation(s)
- Christopher B Mayo
- Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut 06269, USA
| | - C Jason Wong
- Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut 06269, USA
| | - Prisma E Lopez
- Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut 06269, USA
| | - Jeffrey W Lary
- National Analytical Ultracentrifugation Facility, University of Connecticut, Storrs, Connecticut 06269, USA
| | - James L Cole
- Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut 06269, USA Department of Chemistry, University of Connecticut, Storrs, Connecticut 06269, USA National Analytical Ultracentrifugation Facility, University of Connecticut, Storrs, Connecticut 06269, USA
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14
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Liu J, Li Z, Wei Y, Wang W, Wang B, Liang H, Gao Y. Measurement of protein size in concentrated solutions by small angle X-ray scattering. Protein Sci 2016; 25:1385-9. [PMID: 27241796 DOI: 10.1002/pro.2957] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2016] [Revised: 05/26/2016] [Accepted: 05/27/2016] [Indexed: 12/11/2022]
Abstract
By simulations on the distance distribution function (DDF) derived from small angle X-ray scattering (SAXS) theoretical data of a dense monodisperse system, we found a quantitative mathematical correlation between the apparent size of a spherically symmetric (or nearly spherically symmetric) homogenous particle and the concentration of the solution. SAXS experiments on protein solutions of human hemoglobin and horse myoglobin validated the correlation. This gives a new method to determine, from the SAXS DDF, the size of spherically symmetric (or nearly spherically symmetric) particles of a dense monodisperse system, specifically for protein solutions with interference effects.
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Affiliation(s)
- Jun Liu
- Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049, China
| | - Zhihong Li
- Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049, China
| | - Yanru Wei
- Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049, China
| | - Wenjia Wang
- Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049, China
| | - Bing Wang
- CAS Key Laboratory for Biological Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049, China
| | - Hongli Liang
- CAS Key Laboratory for Biological Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049, China
| | - Yuxi Gao
- CAS Key Laboratory for Biological Effects of Nanomaterials and Nanosafety, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049, China
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15
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Gogonea V. Structural Insights into High Density Lipoprotein: Old Models and New Facts. Front Pharmacol 2016; 6:318. [PMID: 26793109 PMCID: PMC4709926 DOI: 10.3389/fphar.2015.00318] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2015] [Accepted: 12/22/2015] [Indexed: 11/13/2022] Open
Abstract
The physiological link between circulating high density lipoprotein (HDL) levels and cardiovascular disease is well-documented, albeit its intricacies are not well-understood. An improved appreciation of HDL function and overall role in vascular health and disease requires at its foundation a better understanding of the lipoprotein's molecular structure, its formation, and its process of maturation through interactions with various plasma enzymes and cell receptors that intervene along the pathway of reverse cholesterol transport. This review focuses on summarizing recent developments in the field of lipid free apoA-I and HDL structure, with emphasis on new insights revealed by newly published nascent and spherical HDL models constructed by combining low resolution structures obtained from small angle neutron scattering (SANS) with contrast variation and geometrical constraints derived from hydrogen-deuterium exchange (HDX), crosslinking mass spectrometry, electron microscopy, Förster resonance energy transfer, and electron spin resonance. Recently published low resolution structures of nascent and spherical HDL obtained from SANS with contrast variation and isotopic labeling of apolipoprotein A-I (apoA-I) will be critically reviewed and discussed in terms of how they accommodate existing biophysical structural data from alternative approaches. The new low resolution structures revealed and also provided some answers to long standing questions concerning lipid organization and particle maturation of lipoproteins. The review will discuss the merits of newly proposed SANS based all atom models for nascent and spherical HDL, and compare them with accepted models. Finally, naturally occurring and bioengineered mutations in apoA-I, and their impact on HDL phenotype, are reviewed and discuss together with new therapeutics employed for restoring HDL function.
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Affiliation(s)
- Valentin Gogonea
- Department of Chemistry, Cleveland State UniversityCleveland, OH, USA; Departments of Cellular and Molecular Medicine and the Center for Cardiovascular Diagnostics and Prevention, Cleveland ClinicCleveland, OH, USA
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16
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Husain B, Mayo C, Cole JL. Role of the Interdomain Linker in RNA-Activated Protein Kinase Activation. Biochemistry 2015; 55:253-61. [PMID: 26678943 DOI: 10.1021/acs.biochem.5b01171] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
RNA-activated protein kinase (PKR) is a key component of the interferon-induced antiviral pathway in higher eukaryotes. Upon recognition of viral dsRNA, PKR is activated via dimerization and autophosphorylation. PKR contains two N-terminal dsRNA binding domains (dsRBD) and a C-terminal kinase domain. The dsRBDs and the kinase are separated by a long, unstructured ∼80-amino acid linker in the human enzyme. The length of the N-terminal portion of the linker varies among PKR sequences, and it is completely absent in one ortholog. Here, we characterize the effects of deleting the variable region from the human enzyme to produce PKRΔV. The linker deletion results in quantitative but not qualitative changes in catalytic activity, RNA binding, and conformation. PKRΔV is somewhat more active and exhibits more cooperative RNA binding. As we previously observed for the full-length enzyme, PKRΔV is flexible in solution and adopts a range of compact and extended conformations. The conformational ensemble is biased toward compact states that might be related to weak interactions between the dsRBD and kinase domains. PKR retains RNA-induced autophosphorylation upon complete removal of the linker, indicating that the C-terminal, basic region is also not required for activity.
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Affiliation(s)
- Bushra Husain
- Department of Molecular and Cell Biology and ‡Department of Chemistry, University of Connecticut , Storrs, Connecticut 06269, United States
| | - Christopher Mayo
- Department of Molecular and Cell Biology and ‡Department of Chemistry, University of Connecticut , Storrs, Connecticut 06269, United States
| | - James L Cole
- Department of Molecular and Cell Biology and ‡Department of Chemistry, University of Connecticut , Storrs, Connecticut 06269, United States
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17
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Husain B, Hesler S, Cole JL. Regulation of PKR by RNA: formation of active and inactive dimers. Biochemistry 2015; 54:6663-72. [PMID: 26488609 DOI: 10.1021/acs.biochem.5b01046] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
PKR is a member of the eIF2α family of protein kinases that inhibit translational initiation in response to stress stimuli and functions as a key mediator of the interferon-induced antiviral response. PKR contains a dsRNA binding domain that binds to duplex regions present in viral RNAs, resulting in kinase activation and autophosphorylation. An emerging theme in the regulation of protein kinases is the allosteric linkage of dimerization and activation. The PKR kinase domain forms a back-to-back parallel dimer that is implicated in activation. We have developed a sensitive homo-Förster resonance energy transfer assay for kinase domain dimerization to directly probe the relationship among RNA binding, activation, and dimerization. In the case of perfect duplex RNAs, dimerization is correlated with activation and dsRNAs containing 30 bp or more efficiently induce kinase domain dimerization and activation. However, more complex duplex RNAs containing a 10-15 bp 2'-O-methyl RNA barrier produce kinase dimers but do not activate. Similarly, inactivating mutations within the PKR dimer interface that disrupt key electrostatic and hydrogen binding interactions fail to abolish dimerization. Our data support a model in which activating RNAs induce formation of a back-to-back parallel PKR kinase dimer whereas nonactivating RNAs either fail to induce dimerization or produce an alternative, inactive dimer configuration, providing an additional mechanism for distinguishing between host and pathogen RNA.
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Affiliation(s)
- Bushra Husain
- Department of Molecular and Cell Biology and ‡Department of Chemistry, University of Connecticut , Storrs, Connecticut 06269, United States
| | - Stephen Hesler
- Department of Molecular and Cell Biology and ‡Department of Chemistry, University of Connecticut , Storrs, Connecticut 06269, United States
| | - James L Cole
- Department of Molecular and Cell Biology and ‡Department of Chemistry, University of Connecticut , Storrs, Connecticut 06269, United States
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18
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Sunita S, Schwartz SL, Conn GL. The Regulatory and Kinase Domains but Not the Interdomain Linker Determine Human Double-stranded RNA-activated Kinase (PKR) Sensitivity to Inhibition by Viral Non-coding RNAs. J Biol Chem 2015; 290:28156-28165. [PMID: 26432638 DOI: 10.1074/jbc.m115.679738] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2015] [Indexed: 12/18/2022] Open
Abstract
Double-stranded RNA (dsRNA)-activated protein kinase (PKR) is an important component of the innate immune system that presents a crucial first line of defense against viral infection. PKR has a modular architecture comprising a regulatory N-terminal dsRNA binding domain and a C-terminal kinase domain interposed by an unstructured ∼80-residue interdomain linker (IDL). Guided by sequence alignment, we created IDL deletions in human PKR (hPKR) and regulatory/kinase domain swap human-rat chimeric PKRs to assess the contributions of each domain and the IDL to regulation of the kinase activity by RNA. Using circular dichroism spectroscopy, limited proteolysis, kinase assays, and isothermal titration calorimetry, we show that each PKR protein is properly folded with similar domain boundaries and that each exhibits comparable polyinosinic-cytidylic (poly(rI:rC)) dsRNA activation profiles and binding affinities for adenoviral virus-associated RNA I (VA RNAI) and HIV-1 trans-activation response (TAR) RNA. From these results we conclude that the IDL of PKR is not required for RNA binding or mediating changes in protein conformation or domain interactions necessary for PKR regulation by RNA. In contrast, inhibition of rat PKR by VA RNAI and TAR RNA was found to be weaker than for hPKR by 7- and >300-fold, respectively, and each human-rat chimeric domain-swapped protein showed intermediate levels of inhibition. These findings indicate that PKR sequence or structural elements in the kinase domain, present in hPKR but absent in rat PKR, are exploited by viral non-coding RNAs to accomplish efficient inhibition of PKR.
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Affiliation(s)
- S Sunita
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322
| | - Samantha L Schwartz
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322
| | - Graeme L Conn
- Department of Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322.
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19
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Liu MS, Wang D, Morimoto H, Yim HCH, Irving AT, Williams BRG, Sadler AJ. Molecular dynamics reveal a novel kinase-substrate interface that regulates protein translation. J Mol Cell Biol 2014; 6:473-85. [PMID: 25404612 DOI: 10.1093/jmcb/mju044] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A key control point in gene expression is the initiation of protein translation, with a universal stress response being constituted by inhibitory phosphorylation of the eukaryotic initiation factor 2α (eIF2α). In humans, four kinases sense diverse physiological stresses to regulate eIF2α to control cell differentiation, adaptation, and survival. Here we develop a computational molecular model of eIF2α and one of its kinases, the protein kinase R, to simulate the dynamics of their interaction. Predictions generated by coarse-grained dynamics simulations suggest a novel mode of action. Experimentation substantiates these predictions, identifying a previously unrecognized interface in the protein complex, which is constituted by dynamic residues in both eIF2α and its kinases that are crucial to regulate protein translation. These findings call for a reinterpretation of the current mechanism of action of the eIF2α kinases and demonstrate the value of conducting computational analysis to evaluate protein function.
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Affiliation(s)
- Ming S Liu
- Centre for Cancer Research, MIMR-PHI Institute of Medical Research, Melbourne, VIC 3168, Australia CSIRO - Computational Informatics and Digital Productivity Flagship, Private Bag 10, Clayton South, VIC 3169, Australia
| | - Die Wang
- Centre for Cancer Research, MIMR-PHI Institute of Medical Research, Melbourne, VIC 3168, Australia
| | - Hiroyuki Morimoto
- Centre for Cancer Research, MIMR-PHI Institute of Medical Research, Melbourne, VIC 3168, Australia Department of Anatomy, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, Fukuoka 807-8555, Japan
| | - Howard C H Yim
- Centre for Cancer Research, MIMR-PHI Institute of Medical Research, Melbourne, VIC 3168, Australia
| | - Aaron T Irving
- Centre for Cancer Research, MIMR-PHI Institute of Medical Research, Melbourne, VIC 3168, Australia
| | - Bryan R G Williams
- Centre for Cancer Research, MIMR-PHI Institute of Medical Research, Melbourne, VIC 3168, Australia Department of Molecular and Translational Science, Monash University, Melbourne, VIC 3168, Australia
| | - Anthony J Sadler
- Centre for Cancer Research, MIMR-PHI Institute of Medical Research, Melbourne, VIC 3168, Australia Department of Molecular and Translational Science, Monash University, Melbourne, VIC 3168, Australia
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20
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van der Lee R, Buljan M, Lang B, Weatheritt RJ, Daughdrill GW, Dunker AK, Fuxreiter M, Gough J, Gsponer J, Jones D, Kim PM, Kriwacki R, Oldfield CJ, Pappu RV, Tompa P, Uversky VN, Wright P, Babu MM. Classification of intrinsically disordered regions and proteins. Chem Rev 2014; 114:6589-631. [PMID: 24773235 PMCID: PMC4095912 DOI: 10.1021/cr400525m] [Citation(s) in RCA: 1415] [Impact Index Per Article: 141.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2013] [Indexed: 12/11/2022]
Affiliation(s)
- Robin van der Lee
- MRC
Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom
- Centre
for Molecular and Biomolecular Informatics, Radboud University Medical Centre, 6500 HB Nijmegen, The
Netherlands
| | - Marija Buljan
- MRC
Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom
| | - Benjamin Lang
- MRC
Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom
| | - Robert J. Weatheritt
- MRC
Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom
| | - Gary W. Daughdrill
- Department
of Cell Biology, Microbiology, and Molecular Biology, University of South Florida, 3720 Spectrum Boulevard, Suite 321, Tampa, Florida 33612, United States
| | - A. Keith Dunker
- Department
of Biochemistry and Molecular Biology, Indiana
University School of Medicine, Indianapolis, Indiana 46202, United States
| | - Monika Fuxreiter
- MTA-DE
Momentum Laboratory of Protein Dynamics, Department of Biochemistry
and Molecular Biology, University of Debrecen, H-4032 Debrecen, Nagyerdei krt 98, Hungary
| | - Julian Gough
- Department
of Computer Science, University of Bristol, The Merchant Venturers Building, Bristol BS8 1UB, United Kingdom
| | - Joerg Gsponer
- Department
of Biochemistry and Molecular Biology, Centre for High-Throughput
Biology, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
| | - David
T. Jones
- Bioinformatics
Group, Department of Computer Science, University
College London, London, WC1E 6BT, United Kingdom
| | - Philip M. Kim
- Terrence Donnelly Centre for Cellular and Biomolecular Research, Department of Molecular
Genetics, and Department of Computer Science, University
of Toronto, Toronto, Ontario M5S 3E1, Canada
| | - Richard
W. Kriwacki
- Department
of Structural Biology, St. Jude Children’s
Research Hospital, Memphis, Tennessee 38105, United States
| | - Christopher J. Oldfield
- Department
of Biochemistry and Molecular Biology, Indiana
University School of Medicine, Indianapolis, Indiana 46202, United States
| | - Rohit V. Pappu
- Department
of Biomedical Engineering and Center for Biological Systems Engineering, Washington University in St. Louis, St. Louis, Missouri 63130, United States
| | - 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
| | - Vladimir N. Uversky
- Department
of Molecular Medicine and USF Health Byrd Alzheimer’s Research
Institute, Morsani College of Medicine, University of South Florida, Tampa, Florida 33612, United States
- Institute for Biological Instrumentation,
Russian Academy of Sciences, Pushchino,
Moscow Region, Russia
| | - Peter
E. Wright
- Department
of Integrative Structural and Computational Biology and Skaggs Institute
of Chemical Biology, The Scripps Research
Institute, 10550 North
Torrey Pines Road, La Jolla, California 92037, United States
| | - M. Madan Babu
- MRC
Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom
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21
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Dzananovic E, Patel TR, Chojnowski G, Boniecki MJ, Deo S, McEleney K, Harding SE, Bujnicki JM, McKenna SA. Solution conformation of adenovirus virus associated RNA-I and its interaction with PKR. J Struct Biol 2013; 185:48-57. [PMID: 24291322 DOI: 10.1016/j.jsb.2013.11.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2013] [Revised: 11/12/2013] [Accepted: 11/23/2013] [Indexed: 11/29/2022]
Abstract
Adenovirus virus-associated RNA (VAI) provides protection against the host antiviral response in part by inhibiting the interferon-induced double stranded RNA-activated protein kinase (PKR). VAI consists of three base-paired regions; the apical stem responsible for the interaction with double-stranded RNA binding motifs (dsRBMs) of PKR, the central stem required for inhibition, and the terminal stem. The solution conformation of VAI and VAI lacking the terminal stem were determined using SAXS that suggested extended conformations that are in agreement with their secondary structures. Solution conformations of VAI lacking the terminal stem in complex with the dsRBMs of PKR indicated that the apical stem interacts with both dsRNA-binding motifs whereas the central stem does not. Hydrodynamic properties calculated from ab initio models were compared to experimentally determined parameters for model validation. Furthermore, SAXS envelopes were used as a constraint for the in silico modeling of tertiary structure for RNA and RNA-protein complex. Finally, full-length PKR was also studied, but concentration-dependent changes in hydrodynamic parameters prevented ab initio shape determination. Taken together, results provide an improved structural framework that further our understanding of the role VAI plays in evading host innate immune responses.
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Affiliation(s)
- Edis Dzananovic
- Department of Chemistry, University of Manitoba, 144 Dysart Road, Winnipeg, Manitoba R3T 2N2, Canada
| | - Trushar R Patel
- Department of Chemistry, University of Manitoba, 144 Dysart Road, Winnipeg, Manitoba R3T 2N2, Canada; School of Biosciences, University of Birmingham, Birmingham B152TT, UK
| | - Grzegorz Chojnowski
- Laboratory of Bioinformatics and Protein Engineering, International Institute of Molecular and Cell Biology, ul. Ks. Trojdena 4, Warsaw 02-109, Poland
| | - Michal J Boniecki
- Laboratory of Bioinformatics and Protein Engineering, International Institute of Molecular and Cell Biology, ul. Ks. Trojdena 4, Warsaw 02-109, Poland
| | - Soumya Deo
- Department of Chemistry, University of Manitoba, 144 Dysart Road, Winnipeg, Manitoba R3T 2N2, Canada
| | - Kevin McEleney
- Department of Chemistry, University of Manitoba, 144 Dysart Road, Winnipeg, Manitoba R3T 2N2, Canada; Manitoba Institute for Materials, University of Manitoba, 144 Dysart Road, Winnipeg, Manitoba R3T 2N2, Canada
| | - Stephen E Harding
- NCMH Laboratory, School of Biosciences, University of Nottingham, Sutton Bonington LE12 5RD, UK
| | - Janusz M Bujnicki
- Laboratory of Bioinformatics and Protein Engineering, International Institute of Molecular and Cell Biology, ul. Ks. Trojdena 4, Warsaw 02-109, Poland; Laboratory of Bioinformatics, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University, ul. Umultowska 89, Poznan 61-614, Poland
| | - Sean A McKenna
- Department of Chemistry, University of Manitoba, 144 Dysart Road, Winnipeg, Manitoba R3T 2N2, Canada; Department of Biochemistry and Medical Genetics, University of Manitoba, 144 Dysart Road, Winnipeg, Manitoba R3T 2N2, Canada.
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22
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Donnelly N, Gorman AM, Gupta S, Samali A. The eIF2α kinases: their structures and functions. Cell Mol Life Sci 2013; 70:3493-511. [PMID: 23354059 PMCID: PMC11113696 DOI: 10.1007/s00018-012-1252-6] [Citation(s) in RCA: 602] [Impact Index Per Article: 54.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2012] [Revised: 12/16/2012] [Accepted: 12/20/2012] [Indexed: 01/02/2023]
Abstract
Cell signaling in response to an array of diverse stress stimuli converges on the phosphorylation of the α-subunit of eukaryotic initiation factor 2 (eIF2). Phosphorylation of eIF2α on serine 51 results in a severe decline in de novo protein synthesis and is an important strategy in the cell's armory against stressful insults including viral infection, the accumulation of misfolded proteins, and starvation. The phosphorylation of eIF2α is carried out by a family of four kinases, PERK (PKR-like ER kinase), PKR (protein kinase double-stranded RNA-dependent), GCN2 (general control non-derepressible-2), and HRI (heme-regulated inhibitor). Each primarily responds to a distinct type of stress or stresses. Thus, while significant sequence similarity exists between the eIF2α kinases in their kinase domains, underlying their common role in phosphorylating eIF2α, additional unique features determine the regulation of these four proteins, that is, what signals activate them. This review will describe the structure of each eIF2α kinase and discuss how this is linked to their activation and function. In parallel to the general translational attenuation elicited by eIF2α kinase activation the translation of stress-induced mRNAs, most notably activating transcription factor 4 (ATF4) is enhanced and these set in motion cascades of gene expression constituting the integrated stress response (ISR), which seek to remediate stress and restore homeostasis. Depending on the cellular context and concurrent signaling pathways active, however, translational attenuation can also facilitate apoptosis. Accordingly, the role of the kinases in determining cell fate will also be discussed.
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Affiliation(s)
- Neysan Donnelly
- Apoptosis Research Center, National University of Ireland, Galway, Ireland
- School of Natural Sciences, National University of Ireland, Galway, Ireland
- Present Address: Department of Molecular Cell Biology, Max Planck Institute of Biochemistry, Am Klopferspitz 18, Martinsried, Munich, 82152 Germany
| | - Adrienne M. Gorman
- Apoptosis Research Center, National University of Ireland, Galway, Ireland
- School of Natural Sciences, National University of Ireland, Galway, Ireland
| | - Sanjeev Gupta
- Apoptosis Research Center, National University of Ireland, Galway, Ireland
- School of Medicine, National University of Ireland, Galway, Ireland
| | - Afshin Samali
- Apoptosis Research Center, National University of Ireland, Galway, Ireland
- School of Natural Sciences, National University of Ireland, Galway, Ireland
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23
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Suits MD, Boraston AB. Structure of the Streptococcus pneumoniae surface protein and adhesin PfbA. PLoS One 2013; 8:e67190. [PMID: 23894284 PMCID: PMC3718772 DOI: 10.1371/journal.pone.0067190] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2013] [Accepted: 05/16/2013] [Indexed: 12/29/2022] Open
Abstract
PfbA (plasmin- and fibronectin-binding protein A) is an extracellular Streptococcus pneumoniae cell-wall attached surface protein that binds to fibronectin, plasmin, and plasminogen. Here we present a structural analysis of the surface exposed domains of PfbA using a combined approach of X-ray crystallography and small-angle X-ray scattering (SAXS). The crystal structure of the PfbA core domain, here called PfbAβ, determined to 2.28 Å resolution revealed an elongated 12-stranded parallel β-helix fold, which structure-based comparisons reveal is most similar to proteins with carbohydrate modifying activity. A notable feature of the PfbAβ is an extensive cleft on one face of the protein with electrochemical and spatial features that are analogous to structurally similar carbohydrate-active enzymes utilizing this feature for substrate accommodation. Though this cleft displays a combination of basic amino acid residues and solvent exposed aromatic amino acids that are distinct features for recognition of carbohydrates, no obvious arrangement of amino acid side chains that would constitute catalytic machinery is evident. The pseudo-atomic SAXS model of a larger fragment of PfbA suggests that it has a relatively well-ordered structure with the N-terminal and core domains of PfbA adopting an extend organization and reveals a novel structural class of surface exposed pneumococcal matrix molecule adhesins.
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Affiliation(s)
- Michael D. Suits
- Department of Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia, Canada
| | - Alisdair B. Boraston
- Department of Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia, Canada
- * E-mail:
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24
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Nallagatla SR, Jones CN, Ghosh SKB, Sharma SD, Cameron CE, Spremulli LL, Bevilacqua PC. Native tertiary structure and nucleoside modifications suppress tRNA's intrinsic ability to activate the innate immune sensor PKR. PLoS One 2013; 8:e57905. [PMID: 23483938 PMCID: PMC3587421 DOI: 10.1371/journal.pone.0057905] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2012] [Accepted: 01/28/2013] [Indexed: 11/17/2022] Open
Abstract
Interferon inducible protein kinase PKR is an essential component of innate immunity. It is activated by long stretches of dsRNA and provides the first line of host defense against pathogens by inhibiting translation initiation in the infected cell. Many cellular and viral transcripts contain nucleoside modifications and/or tertiary structure that could affect PKR activation. We have previously demonstrated that a 5'-end triphosphate-a signature of certain viral and bacterial transcripts-confers the ability of relatively unstructured model RNA transcripts to activate PKR to inhibit translation, and that this activation is abrogated by certain modifications present in cellular RNAs. In order to understand the biological implications of native RNA tertiary structure and nucleoside modifications on PKR activation, we study here the heavily modified cellular tRNAs and the unmodified or the lightly modified mitochondrial tRNAs (mt-tRNA). We find that both a T7 transcript of yeast tRNA(Phe) and natively extracted total bovine liver mt-tRNA activate PKR in vitro, whereas native E. coli, bovine liver, yeast, and wheat tRNA(Phe) do not, nor do a variety of base- or sugar-modified T7 transcripts. These results are further supported by activation of PKR by a natively folded T7 transcript of tRNA(Phe)in vivo supporting the importance of tRNA modification in suppressing PKR activation in cells. We also examine PKR activation by a T7 transcript of the A14G pathogenic mutant of mt-tRNA(Leu), which is known to dimerize, and find that the misfolded dimeric form activates PKR in vitro while the monomeric form does not. Overall, the in vitro and in vivo findings herein indicate that tRNAs have an intrinsic ability to activate PKR and that nucleoside modifications and native RNA tertiary folding may function, at least in part, to suppress such activation, thus serving to distinguish self and non-self tRNA in innate immunity.
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Affiliation(s)
- Subba Rao Nallagatla
- Department of Chemistry and Center for RNA Molecular Biology, The Pennsylvania State University, University Park, PA, USA
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25
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Li F, Li S, Wang Z, Shen Y, Zhang T, Yang X. Structure of the kinase domain of human RNA-dependent protein kinase with K296R mutation reveals a face-to-face dimer. CHINESE SCIENCE BULLETIN-CHINESE 2013. [DOI: 10.1007/s11434-012-5461-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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26
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Dzananovic E, Patel TR, Deo S, McEleney K, Stetefeld J, McKenna SA. Recognition of viral RNA stem-loops by the tandem double-stranded RNA binding domains of PKR. RNA (NEW YORK, N.Y.) 2013; 19:333-344. [PMID: 23329698 PMCID: PMC3677244 DOI: 10.1261/rna.035931.112] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2012] [Accepted: 12/12/2012] [Indexed: 05/30/2023]
Abstract
In humans, the double-stranded RNA (dsRNA)-activated protein kinase (PKR) is expressed in late stages of the innate immune response to viral infection by the interferon pathway. PKR consists of tandem dsRNA binding motifs (dsRBMs) connected via a flexible linker to a Ser/Thr kinase domain. Upon interaction with viral dsRNA, PKR is converted into a catalytically active enzyme capable of phosphorylating a number of target proteins that often results in host cell translational repression. A number of high-resolution structural studies involving individual dsRBMs from proteins other than PKR have highlighted the key features required for interaction with perfectly duplexed RNA substrates. However, viral dsRNA molecules are highly structured and often contain deviations from perfect A-form RNA helices. By use of small-angle X-ray scattering (SAXS), we present solution conformations of the tandem dsRBMs of PKR in complex with two imperfectly base-paired viral dsRNA stem-loops; HIV-1 TAR and adenovirus VA(I)-AS. Both individual components and complexes were purified by size exclusion chromatography and characterized by dynamic light scattering at multiple concentrations to ensure monodispersity. SAXS ab initio solution conformations of the individual components and RNA-protein complexes were determined and highlight the potential of PKR to interact with both stem and loop regions of the RNA. Excellent agreement between experimental and model-based hydrodynamic parameter determination heightens our confidence in the obtained models. Taken together, these data support and provide a framework for the existing biochemical data regarding the tolerance of imperfectly base-paired viral dsRNA by PKR.
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Affiliation(s)
- Edis Dzananovic
- Department of Chemistry, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada
| | - Trushar R. Patel
- Department of Chemistry, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada
| | - Soumya Deo
- Department of Chemistry, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada
| | - Kevin McEleney
- Department of Chemistry, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada
- Manitoba Institute for Materials, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada
| | - Jörg Stetefeld
- Department of Chemistry, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada
- Manitoba Group in Protein Structure and Function, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada
| | - Sean A. McKenna
- Department of Chemistry, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada
- Manitoba Group in Protein Structure and Function, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada
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27
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Pluvinage B, Chitayat S, Ficko-Blean E, Abbott DW, Kunjachen JM, Grondin J, Spencer HL, Smith SP, Boraston AB. Conformational Analysis of StrH, the Surface-Attached exo-β-d-N-Acetylglucosaminidase from Streptococcus pneumoniae. J Mol Biol 2013; 425:334-49. [DOI: 10.1016/j.jmb.2012.11.005] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2012] [Revised: 11/05/2012] [Accepted: 11/06/2012] [Indexed: 12/22/2022]
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28
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Patel S, Blose JM, Sokoloski JE, Pollack L, Bevilacqua PC. Specificity of the double-stranded RNA-binding domain from the RNA-activated protein kinase PKR for double-stranded RNA: insights from thermodynamics and small-angle X-ray scattering. Biochemistry 2012; 51:9312-22. [PMID: 23140277 DOI: 10.1021/bi300935p] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The interferon-inducible, double-stranded (ds) RNA-activated protein kinase (PKR) contains a dsRNA-binding domain (dsRBD) and plays key roles in viral pathogenesis and innate immunity. Activation of PKR is typically mediated by long dsRNA, and regulation of PKR is disfavored by most RNA imperfections, including bulges and internal loops. Herein, we combine isothermal titration calorimetry (ITC), electrophoretic mobility shift assays, and small-angle X-ray scattering (SAXS) to dissect the thermodynamic basis for the specificity of the dsRBD termed "p20" for various RNAs and to detect any RNA conformational changes induced upon protein binding. We monitor binding of p20 to chimeric duplexes containing terminal RNA-DNA hybrid segments and a central dsRNA segment, which was either unbulged ("perfect") or bulged. The ITC data reveal strong binding of p20 to the perfect duplex (K(d) ~ 30 nM) and weaker binding to the bulged duplex (K(d) ~ 2-5 μM). SAXS reconstructions and p(r) distance distribution functions further uncover that p20 induces no significant conformational change in perfect dsRNA but largely straightens bulged dsRNA. Together, these observations support the dsRBD's ability to tightly bind to only A-form RNA and suggest that in a noninfected cell, PKR may be buffered via weak interactions with various bulged and looped RNAs, which it may straighten. This work suggests that PKR-regulating RNAs with complex secondary and tertiary structures likely mimic dsRNA and/or engage portions of PKR outside of the dsRBD.
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Affiliation(s)
- Sunita Patel
- Department of Chemistry and Center for RNA Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
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Bernadó P, Svergun DI. Structural analysis of intrinsically disordered proteins by small-angle X-ray scattering. MOLECULAR BIOSYSTEMS 2011; 8:151-67. [PMID: 21947276 DOI: 10.1039/c1mb05275f] [Citation(s) in RCA: 259] [Impact Index Per Article: 19.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Small-angle scattering of X-rays (SAXS) is an established method to study the overall structure and structural transitions of biological macromolecules in solution. For folded proteins, the technique provides three-dimensional low resolution structures ab initio or it can be used to drive rigid-body modeling. SAXS is also a powerful tool for the quantitative analysis of flexible systems, including intrinsically disordered proteins (IDPs), and is highly complementary to the high resolution methods of X-ray crystallography and NMR. Here we present the basic principles of SAXS and review the main approaches to the characterization of IDPs and flexible multidomain proteins using SAXS. Together with the standard approaches based on the analysis of overall parameters, a recently developed Ensemble Optimization Method (EOM) is now available. The latter method allows for the co-existence of multiple protein conformations in solution compatible with the scattering data. Analysis of the selected ensembles provides quantitative information about flexibility and also offers insights into structural features. Examples of the use of SAXS and combined approaches with NMR, X-ray crystallography, and computational methods to characterize completely or partially disordered proteins are presented.
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Affiliation(s)
- Pau Bernadó
- Institute for Research in Biomedicine, Parc Científic de Barcelona, Barcelona, Spain.
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30
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Abstract
PKR is an interferon-induced kinase that plays a pivotal role in the innate immunity pathway for defense against viral infection. PKR is activated to undergo autophosphorylation upon binding to RNAs that contain duplex regions. Some highly structured viral RNAs do not activate and function as PKR inhibitors. In order to define the mechanisms of activation and inhibition of PKR by RNA, it is necessary to characterize the stoichiometries, affinities, and free energy couplings governing the assembly of the relevant complexes. We have found sedimentation velocity analytical ultracentrifugation to be particularly useful in the study of PKR-RNA interactions. Here, we describe protocols for designing and analyzing sedimentation velocity experiments that are generally applicable to studies of protein-nucleic acid interactions. Initially, velocity data obtained at multiple protein:RNA ratios are analyzed using the dc/dt method's to define the association model and to test whether the system is kinetically limited. The sedimentation velocity data obtained at multiple loading concentrations are then globally fitted to this model to determine the relevant association constants. The frictional ratios of the complexes are calculated using the fitted sedimentation coefficients to determine whether the hydrodynamic properties are physically reasonable. We demonstrate the utility of this approach using examples from our studies of PKR interactions with simple dsRNAs, the HIV TAR RNA, and the VAI RNA from adenovirus.
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Affiliation(s)
- C Jason Wong
- Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut, USA
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31
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SAXS ensemble refinement of ESCRT-III CHMP3 conformational transitions. Structure 2011; 19:109-16. [PMID: 21220121 DOI: 10.1016/j.str.2010.10.006] [Citation(s) in RCA: 206] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2010] [Revised: 09/22/2010] [Accepted: 10/20/2010] [Indexed: 11/20/2022]
Abstract
We developed and implemented an ensemble-refinement method to study dynamic biomolecular assemblies with intrinsically disordered segments. Data from small angle X-ray scattering (SAXS) experiments and from coarse-grained molecular simulations were combined by using a maximum-entropy approach. The method was applied to CHMP3 of ESCRT-III, a protein with multiple helical domains separated by flexible linkers. Based on recent SAXS data by Lata et al. (J. Mol. Biol. 378, 818, 2008), we constructed ensembles of CHMP3 at low- and high-salt concentration to characterize its closed autoinhibited state and open active state. At low salt, helix α(5) is bound to the tip of helices α(1) and α(2), in excellent agreement with a recent crystal structure. Helix α(6) remains free in solution and does not appear to be part of the autoinhibitory complex. The simulation-based ensemble refinement is general and effectively increases the resolution of SAXS beyond shape information to atomically detailed structures.
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32
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Nallagatla SR, Toroney R, Bevilacqua PC. Regulation of innate immunity through RNA structure and the protein kinase PKR. Curr Opin Struct Biol 2010; 21:119-27. [PMID: 21145228 DOI: 10.1016/j.sbi.2010.11.003] [Citation(s) in RCA: 108] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2010] [Revised: 11/04/2010] [Accepted: 11/09/2010] [Indexed: 12/25/2022]
Abstract
Molecular recognition of RNA structure is key to innate immunity. The protein kinase PKR differentiates self from non-self by recognition of molecular patterns in RNA. Certain biological RNAs induce autophosphorylation of PKR, activating it to phosphorylate eukaryotic initiation factor 2α (eIF2α), which leads to inhibition of translation. Additional biological RNAs inhibit PKR, while still others have no effect. The aim of this article is to develop a cohesive framework for understanding and predicting PKR function in the context of diverse RNA structure. We present effects of recently characterized viral and cellular RNAs on regulation of PKR, as well as siRNAs. A central conclusion is that assembly of accessible long double-stranded RNA (dsRNA) elements within biological RNAs plays a key role in regulation of PKR kinase. Strategies for forming such elements include RNA dimerization, formation of symmetrical helical defects, A-form dsRNA mimicry, and coaxial stacking of helices.
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Affiliation(s)
- Subba Rao Nallagatla
- Department of Chemistry, The Pennsylvania State University, 104 Chemistry Bldg, University Park, PA 16802, USA
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33
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Sadler AJ. Orchestration of the activation of protein kinase R by the RNA-binding motif. J Interferon Cytokine Res 2010; 30:195-204. [PMID: 20377414 DOI: 10.1089/jir.2010.0005] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The protein kinase R (PKR) constitutes part of the host antiviral response. PKR activation is regulated by the N-terminus of protein, which encodes tandem RNA-binding motifs (RBMs). The full capabilities of RBMs from PKR and other proteins have surpassed the narrow specificities initially determined as merely binding double-stranded RNA. Recognition of the increased affinity of the RBM for additional RNA species has established an immunological distinction by which PKR can detect exogenous RNAs, as well as identified PKR-mediated expression of specific endogenous genes. Furthermore, as RBMs also mediate interactions with other proteins, including PKR itself, this motif connects PKR to the broader RNA metabolism. Given the fundamental importance of protein-RNA interactions, not only in the innate immune response to intracellular pathogens, but also to coordinate the cellular replication machinery, there is considerable interest in the mechanisms by which proteins recognize and respond to RNA. This review appraises our understanding of how PKR activity is modulated by the RBMs.
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Affiliation(s)
- Anthony J Sadler
- Monash Institute of Medical Research, Monash University, Melbourne, Australia
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34
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Magnesium-dependent interaction of PKR with adenovirus VAI. J Mol Biol 2010; 402:638-44. [PMID: 20713064 DOI: 10.1016/j.jmb.2010.08.015] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2010] [Revised: 08/06/2010] [Accepted: 08/09/2010] [Indexed: 01/08/2023]
Abstract
Protein kinase R (PKR) is an interferon-induced kinase that plays a pivotal role in the innate immunity pathway for defense against viral infection. PKR is activated to undergo autophosphorylation upon binding to RNAs that contain duplex regions. Activated PKR phosphorylates the α-subunit of eukaryotic initiation factor 2, thereby inhibiting protein synthesis in virus-infected cells. Viruses have evolved diverse PKR-inhibitory strategies to evade the antiviral response. Adenovirus encodes virus-associated RNA I (VAI), a highly structured RNA inhibitor that binds PKR but fails to activate. We have characterized the stoichiometry and affinity of PKR binding to define the mechanism of PKR inhibition by VAI. Sedimentation velocity and isothermal titration calorimetry measurements indicate that PKR interactions with VAI are modulated by Mg(2+). Two PKR monomers bind in the absence of Mg(2+), but a single monomer binds in the presence of divalent ion. Known RNA activators of PKR are capable of binding multiple PKR monomers to allow the kinase domains to come into close proximity and thus enhance dimerization. We propose that VAI acts as an inhibitor of PKR because it binds and sequesters a single PKR in the presence of divalent cation.
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35
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Anderson E, Quartararo C, Brown RS, Shi Y, Yao X, Cole JL. Analysis of monomeric and dimeric phosphorylated forms of protein kinase R. Biochemistry 2010; 49:1217-25. [PMID: 20088595 DOI: 10.1021/bi901873p] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
PKR (protein kinase R) is induced by interferon and is a key component of the innate immunity antiviral pathway. Upon binding double-stranded RNA (dsRNA) or dimerization in the absence of dsRNA, PKR undergoes autophosphorylation at multiple serines and threonines that activate the kinase. Although it has previously been demonstrated that phosphorylation enhances PKR dimerization, gel filtration analysis reveals a second monomeric phosphorylated form. These forms are termed phosphorylated dimeric PKR (pPKRd) and phosphorylated monomeric PKR (pPKRm). These two forms do not reversibly interconvert. Sedimentation equilibrium measurements reveal that pPKRm dimerizes weakly with a K(d) similar to that of unphosphorylated PKR. Isoelectric focusing and mass spectrometry demonstrate that both pPKRm and pPKRd are heterogeneous in their phosphorylation states, with an average of 9 or 10 phosphates. Equilibrium chemical denaturation analysis indicates that phosphorylation destabilizes the kinase domain by approximately 1.5 kcal/mol in the dimeric form but not in the monomeric form. Limited proteolysis also reveals that phosphorylation induces a conformational change in pPKRd that is not detected in pPKRm. pPKRm binds dsRNA with an affinity similar to that of unphosphorylated PKR, whereas binding cannot be detected with pPKRd. Despite these substantial differences in biophysical properties, both pPKRm and pPKRd are catalytically competent and are activated to phosphorylate the PKR substrate eIF2alpha in the absence of dsRNA. Thus, both monomeric and dimeric forms of phosphorylated PKR may participate in the interferon antiviral pathway.
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Affiliation(s)
- Eric Anderson
- Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut 06269, USA
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36
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Jacques DA, Trewhella J. Small-angle scattering for structural biology--expanding the frontier while avoiding the pitfalls. Protein Sci 2010; 19:642-57. [PMID: 20120026 PMCID: PMC2867006 DOI: 10.1002/pro.351] [Citation(s) in RCA: 303] [Impact Index Per Article: 21.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2009] [Revised: 01/17/2010] [Accepted: 01/19/2010] [Indexed: 12/18/2022]
Abstract
The last decade has seen a dramatic increase in the use of small-angle scattering for the study of biological macromolecules in solution. The drive for more complete structural characterization of proteins and their interactions, coupled with the increasing availability of instrumentation and easy-to-use software for data analysis and interpretation, is expanding the utility of the technique beyond the domain of the biophysicist and into the realm of the protein scientist. However, the absence of publication standards and the ease with which 3D models can be calculated against the inherently 1D scattering data means that an understanding of sample quality, data quality, and modeling assumptions is essential to have confidence in the results. This review is intended to provide a road map through the small-angle scattering experiment, while also providing a set of guidelines for the critical evaluation of scattering data. Examples of current best practice are given that also demonstrate the power of the technique to advance our understanding of protein structure and function.
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Affiliation(s)
| | - Jill Trewhella
- School of Molecular and Microbial Biosciences, The University of SydneySydney, New South Wales 2006, Australia
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Effect of interdomain dynamics on the structure determination of modular proteins by small-angle scattering. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2009; 39:769-80. [DOI: 10.1007/s00249-009-0549-3] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2009] [Revised: 09/10/2009] [Accepted: 09/24/2009] [Indexed: 01/08/2023]
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38
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Heinicke LA, Wong CJ, Lary J, Nallagatla SR, Diegelman-Parente A, Zheng X, Cole JL, Bevilacqua PC. RNA dimerization promotes PKR dimerization and activation. J Mol Biol 2009; 390:319-38. [PMID: 19445956 DOI: 10.1016/j.jmb.2009.05.005] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2009] [Revised: 05/06/2009] [Accepted: 05/07/2009] [Indexed: 01/12/2023]
Abstract
The double-stranded RNA (dsRNA)-activated protein kinase [protein kinase R (PKR)] plays a major role in the innate immune response in humans. PKR binds dsRNA non-sequence specifically and requires a minimum of 15-bp dsRNA for one protein to bind and 30-bp dsRNA to induce protein dimerization and activation by autophosphorylation. PKR phosphorylates eukaryotic initiation factor 2alpha, a translation initiation factor, resulting in the inhibition of protein synthesis. We investigated the mechanism of PKR activation by an RNA hairpin with a number of base pairs intermediate between these 15- to 30-bp limits: human immunodeficiency virus type 1 transactivation-responsive region (TAR) RNA, a 23-bp hairpin with three bulges that is known to dimerize. TAR monomers and dimers were isolated from native gels and assayed for RNA and protein dimerization to test whether RNA dimerization affects PKR dimerization and activation. To modulate the extent of dimerization, we included TAR mutants with different secondary features. Native gel mixing experiments and analytical ultracentrifugation indicate that TAR monomers bind one PKR monomer and that TAR dimers bind two or three PKRs, demonstrating that RNA dimerization drives the binding of multiple PKR molecules. Consistent with functional dimerization of PKR, TAR dimers activated PKR while TAR monomers did not, and RNA dimers with fewer asymmetrical secondary-structure defects, as determined by enzymatic structure mapping, were more potent activators. Thus, the secondary-structure defects in the TAR RNA stem function as antideterminants to PKR binding and activation. Our studies support that dimerization of a 15- to 30-bp hairpin RNA, which effectively doubles its length, is a key step in driving activation of PKR and provide a model for how RNA folding can be related to human disease.
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Affiliation(s)
- Laurie A Heinicke
- Department of Chemistry, Pennsylvania State University, University Park, 16802, USA
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