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Jaramillo-Martinez V, Dominguez MJ, Bell GM, Souness ME, Carhart AH, Cuibus MA, Masoumzadeh E, Lantz BJ, Adkins AJ, Latham MP, Ball KA, Stollar EJ. How a highly acidic SH3 domain folds in the absence of its charged peptide target. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.03.21.532811. [PMID: 36993259 PMCID: PMC10055188 DOI: 10.1101/2023.03.21.532811] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/31/2023]
Abstract
Charged residues on the surface of proteins are critical for both protein stability and interactions. However, many proteins contain binding regions with a high net-charge that may destabilize the protein but are useful for binding to oppositely charged targets. We hypothesized that these domains would be marginally stable, as electrostatic repulsion would compete with favorable hydrophobic collapse during folding. Furthermore, by increasing the salt concentration we predict that these protein folds would be stabilized by mimicking some of the favorable electrostatic interactions that take place during target binding. We varied the salt and urea concentrations to probe the contributions of electrostatic and hydrophobic interactions for the folding of the 60-residue yeast SH3 domain found in Abp1p. The SH3 domain was significantly stabilized with increased salt concentrations according to the Debye-Huckel limiting law. Molecular dynamics and NMR show that sodium ions interact with all 15 acidic residues but do little to change backbone dynamics or overall structure. Folding kinetics experiments show that the addition of urea or salt primarily affects the folding rate, indicating that almost all the hydrophobic collapse and electrostatic repulsion occurs in the transition state. After the transition state formation, modest yet favorable short-range salt-bridges are formed along with hydrogen bonds, as the native state fully folds. Thus, hydrophobic collapse offsets electrostatic repulsion to ensure this highly charged binding domain can still fold and be ready to bind to its charged peptide targets, a property that is likely evolutionarily conserved over one billion years. Statement for broader audience Some protein domains are highly charged because they are adapted to bind oppositely charged proteins and nucleic acids. However, it is unknown how these highly charged domains fold as during folding there will be significant repulsion between like-charges. We investigate how one of these highly charged domains folds in the presence of salt, which can screen the charge repulsion and make folding easier, allowing us to understand how folding occurs despite the protein’s high charge. Supplementary material Supplementary material document containing additional details on protein expression methods, thermodynamics and kinetics equations, and the effect of urea on electrostatic interactions, as well as 4 supplemental figures and 4 supplemental data tables. ( Supplementary_Material.docx ), 15 pages Supplemental excel file containing covariation data across AbpSH3 orthologs ( FileS1.xlsx ).
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Bondos SE, Dunker AK, Uversky VN. Intrinsically disordered proteins play diverse roles in cell signaling. Cell Commun Signal 2022; 20:20. [PMID: 35177069 PMCID: PMC8851865 DOI: 10.1186/s12964-022-00821-7] [Citation(s) in RCA: 56] [Impact Index Per Article: 28.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2021] [Accepted: 12/11/2021] [Indexed: 11/29/2022] Open
Abstract
Abstract Signaling pathways allow cells to detect and respond to a wide variety of chemical (e.g. Ca2+ or chemokine proteins) and physical stimuli (e.g., sheer stress, light). Together, these pathways form an extensive communication network that regulates basic cell activities and coordinates the function of multiple cells or tissues. The process of cell signaling imposes many demands on the proteins that comprise these pathways, including the abilities to form active and inactive states, and to engage in multiple protein interactions. Furthermore, successful signaling often requires amplifying the signal, regulating or tuning the response to the signal, combining information sourced from multiple pathways, all while ensuring fidelity of the process. This sensitivity, adaptability, and tunability are possible, in part, due to the inclusion of intrinsically disordered regions in many proteins involved in cell signaling. The goal of this collection is to highlight the many roles of intrinsic disorder in cell signaling. Following an overview of resources that can be used to study intrinsically disordered proteins, this review highlights the critical role of intrinsically disordered proteins for signaling in widely diverse organisms (animals, plants, bacteria, fungi), in every category of cell signaling pathway (autocrine, juxtacrine, intracrine, paracrine, and endocrine) and at each stage (ligand, receptor, transducer, effector, terminator) in the cell signaling process. Thus, a cell signaling pathway cannot be fully described without understanding how intrinsically disordered protein regions contribute to its function. The ubiquitous presence of intrinsic disorder in different stages of diverse cell signaling pathways suggest that more mechanisms by which disorder modulates intra- and inter-cell signals remain to be discovered. Graphical abstract ![]()
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Affiliation(s)
- Sarah E Bondos
- Department of Molecular and Cellular Medicine, Texas A&M Health Science Center, College Station, TX, 77843, USA.
| | - A Keith Dunker
- Center for Computational Biology and Bioinformatics, Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN, 46202, USA
| | - Vladimir N Uversky
- Department of Molecular Medicine and USF Health Byrd Alzheimer's Research Institute, Morsani College of Medicine, University of South Florida, Tampa, FL, 33612, USA.,Institute for Biological Instrumentation of the Russian Academy of Sciences, Federal Research Center "Pushchino Scientific Center for Biological Research of the Russian Academy of Sciences", Pushchino, Moscow Region, Russia, 142290
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Multivalency enables unidirectional switch-like competition between intrinsically disordered proteins. Proc Natl Acad Sci U S A 2022; 119:2117338119. [PMID: 35012986 PMCID: PMC8784115 DOI: 10.1073/pnas.2117338119] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/22/2021] [Indexed: 12/31/2022] Open
Abstract
Intrinsically disordered proteins must compete for binding to common regulatory targets to carry out their biological functions. Previously, we showed that the activation domains of two disordered proteins, the transcription factor HIF-1α and its negative regulator CITED2, function as a unidirectional, allosteric molecular switch to control transcription of critical adaptive genes under conditions of oxygen deprivation. These proteins achieve transcriptional control by competing for binding to the TAZ1 domain of the transcriptional coactivators CREB-binding protein (CBP) and p300 (CREB: cyclic-AMP response element binding protein). To characterize the mechanistic details behind this molecular switch, we used solution NMR spectroscopy and complementary biophysical methods to determine the contributions of individual binding motifs in CITED2 to the overall competition process. An N-terminal region of the CITED2 activation domain, which forms a helix when bound to TAZ1, plays a critical role in initiating competition with HIF-1α by enabling formation of a ternary complex in a process that is highly dependent on the dynamics and disorder of the competing partners. Two other conserved binding motifs in CITED2, the LPEL motif and an aromatic/hydrophobic motif that we term ϕC, function synergistically to enhance binding of CITED2 and inhibit rebinding of HIF-1α. The apparent unidirectionality of competition between HIF-1α and CITED2 is lost when one or more of these binding regions is altered by truncation or mutation of the CITED2 peptide. Our findings illustrate the complexity of molecular interactions involving disordered proteins containing multivalent interaction motifs and provide insight into the unique mechanisms by which disordered proteins compete for occupancy of common molecular targets within the cell.
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Alcantara J, Stix R, Huang K, Connor A, East R, Jaramillo-Martinez V, Stollar EJ, Ball KA. An Unbound Proline-Rich Signaling Peptide Frequently Samples Cis Conformations in Gaussian Accelerated Molecular Dynamics Simulations. Front Mol Biosci 2021; 8:734169. [PMID: 34869581 PMCID: PMC8634643 DOI: 10.3389/fmolb.2021.734169] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Accepted: 10/27/2021] [Indexed: 11/13/2022] Open
Abstract
Disordered proline-rich motifs are common across the proteomes of many species and are often involved in protein-protein interactions. Proline is a unique amino acid due to the covalent bond between the backbone nitrogen and the proline side chain. The resulting five-membered ring allows proline to sample the cis state about its peptide bond, which other residues cannot do as readily. Because proline-rich disordered sequences exist as ensembles that likely include structures with the proline peptide bond in cis, a robust methodology to accurately account for these conformations in the overall ensemble is crucial. Observing the cis conformations of proline in a disordered sequence is challenging both experimentally and computationally. Nitrogen-hydrogen NMR spectroscopy cannot directly observe proline residues, which lack an amide bond, and computational methods struggle to overcome the large kinetic barrier between the cis and trans states, since isomerization usually occurs on the order of seconds. In the current work, Gaussian accelerated molecular dynamics was used to overcome this free energy barrier and simulate proline isomerization in a tetrapeptide (KPTP) and in the 12-residue proline-rich SH3 binding peptide, ArkA. We found that Gaussian accelerated molecular dynamics, when combined with a lowered peptide bond dihedral angle potential energy barrier (15 kcal/mol), allowed sufficient sampling of the proline cis and trans states on a microsecond timescale. All ArkA prolines spend a significant fraction of time in cis, leading to a more compact ensemble with less polyproline II helix structure than an ArkA ensemble with all peptide bonds in trans. The ensemble containing cis prolines also matches more closely to in vitro circular dichroism data than the all-trans ensemble. The ability of the ArkA prolines to isomerize likely affects the peptide's ability to bind its partner SH3 domain, and should be studied further. This is the first molecular dynamics simulation study of proline isomerization in a biologically relevant proline-rich sequence that we know of, and a similar protocol could be applied to study multi-proline isomerization in other proline-containing proteins to improve conformational diversity and agreement with in vitro data.
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Affiliation(s)
- Juan Alcantara
- Department of Chemistry, Skidmore College, Saratoga Springs, NY, United States
| | - Robyn Stix
- Department of Chemistry, Skidmore College, Saratoga Springs, NY, United States
| | - Katherine Huang
- Department of Chemistry, Skidmore College, Saratoga Springs, NY, United States
| | - Acadia Connor
- Department of Chemistry, Skidmore College, Saratoga Springs, NY, United States
| | - Ray East
- Department of Chemistry, Skidmore College, Saratoga Springs, NY, United States
| | - Valeria Jaramillo-Martinez
- Department of Neuroscience and Pharmacology, Texas Teach University Health Science Center, Lubbock, TX, United States
| | - Elliott J Stollar
- School of Life Sciences, University of Liverpool, Liverpool, United Kingdom
| | - K Aurelia Ball
- Department of Chemistry, Skidmore College, Saratoga Springs, NY, United States
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Sacquin-Mora S, Prévost C. When Order Meets Disorder: Modeling and Function of the Protein Interface in Fuzzy Complexes. Biomolecules 2021; 11:1529. [PMID: 34680162 PMCID: PMC8533853 DOI: 10.3390/biom11101529] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2021] [Revised: 10/11/2021] [Accepted: 10/12/2021] [Indexed: 11/30/2022] Open
Abstract
The degree of proteins structural organization ranges from highly structured, compact folding to intrinsic disorder, where each degree of self-organization corresponds to specific functions: well-organized structural motifs in enzymes offer a proper environment for precisely positioned functional groups to participate in catalytic reactions; at the other end of the self-organization spectrum, intrinsically disordered proteins act as binding hubs via the formation of multiple, transient and often non-specific interactions. This review focusses on cases where structurally organized proteins or domains associate with highly disordered protein chains, leading to the formation of interfaces with varying degrees of fuzziness. We present a review of the computational methods developed to provide us with information on such fuzzy interfaces, and how they integrate experimental information. The discussion focusses on two specific cases, microtubules and homologous recombination nucleoprotein filaments, where a network of intrinsically disordered tails exerts regulatory function in recruiting partner macromolecules, proteins or DNA and tuning the atomic level association. Notably, we show how computational approaches such as molecular dynamics simulations can bring new knowledge to help bridging the gap between experimental analysis, that mostly concerns ensemble properties, and the behavior of individual disordered protein chains that contribute to regulation functions.
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Affiliation(s)
- Sophie Sacquin-Mora
- CNRS, Laboratoire de Biochimie Théorique, UPR9080, Université de Paris, 13 Rue Pierre et Marie Curie, 75005 Paris, France;
- Institut de Biologie Physico-Chimique, Fondation Edmond de Rothschild, PSL Research University, 75006 Paris, France
| | - Chantal Prévost
- CNRS, Laboratoire de Biochimie Théorique, UPR9080, Université de Paris, 13 Rue Pierre et Marie Curie, 75005 Paris, France;
- Institut de Biologie Physico-Chimique, Fondation Edmond de Rothschild, PSL Research University, 75006 Paris, France
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Sun B, Kekenes-Huskey PM. Assessing the Role of Calmodulin's Linker Flexibility in Target Binding. Int J Mol Sci 2021; 22:ijms22094990. [PMID: 34066691 PMCID: PMC8125811 DOI: 10.3390/ijms22094990] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2021] [Revised: 04/21/2021] [Accepted: 04/28/2021] [Indexed: 12/17/2022] Open
Abstract
Calmodulin (CaM) is a highly-expressed Ca2+ binding protein known to bind hundreds of protein targets. Its binding selectivity to many of these targets is partially attributed to the protein’s flexible alpha helical linker that connects its N- and C-domains. It is not well established how its linker mediates CaM’s binding to regulatory targets yet. Insights into this would be invaluable to understanding its regulation of diverse cellular signaling pathways. Therefore, we utilized Martini coarse-grained (CG) molecular dynamics simulations to probe CaM/target assembly for a model system: CaM binding to the calcineurin (CaN) regulatory domain. The simulations were conducted assuming a ‘wild-type’ calmodulin with normal flexibility of its linker, as well as a labile, highly-flexible linker variant to emulate structural changes that could be induced, for instance, by post-translational modifications. For the wild-type model, 98% of the 600 simulations across three ionic strengths adopted a bound complex within 2 μs of simulation time; of these, 1.7% sampled the fully-bound state observed in the experimentally-determined crystallographic structure. By calculating the mean-first-passage-time for these simulations, we estimated the association rate to be ka= 8.7 × 108 M−1 s−1, which is similar to the diffusion-limited, experimentally-determined rate of 2.2 × 108 M−1 s−1. Furthermore, our simulations recapitulated its well-known inverse relationship between the association rate and the solution ionic strength. In contrast, although over 97% of the labile linker simulations formed tightly-bound complexes, only 0.3% achieved the fully-bound configuration. This effect appears to stem from a difference in the ensembles of extended and collapsed states which are controlled by the linker flexibility. Therefore, our simulations suggest that variations in the CaM linker’s propensity for alpha helical secondary structure can modulate the kinetics of target binding.
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