bims-indpro Biomed News
on Intrinsically disordered proteins
Issue of 2022–10–23
eightteen papers selected by
Sara Mingu, Johannes Gutenberg University



  1. Int J Biol Macromol. 2022 Oct 15. pii: S0141-8130(22)02339-X. [Epub ahead of print]
      Structural biology of proteins emphasises that proteins ought to have an ordered structure to perform their biological role optimally. The over-reliance on the ordered structure of proteins is now slowly shifting towards a more comprehensive discussion platform. Intrinsically disordered proteins (IDPs) and intrinsically disordered protein regions (IDPRs) are gaining momentum in protein structural biology as we update ourselves with evolutionary traits and functional importance in various organisms. The evolution and functional significance of this diverse class of protein conformations are based on sequence exhibition, structural attainment, and interactions with their immediate surroundings. In this review, we emphasise the evolutionary status of disordered proteins and correlate their functional importance in the physiology of specific organisms. We aim to close this review by establishing a positive correlation between IDPs and their importance in human health and future medicine. Establishing firm roles of IDPs and IDPRs with extensive research will help expand the field of structural biology, helping us understand the fundamentals of protein folding and misfolding, associated diseases and drug design.
    Keywords:  Amyloids; Drug development; Intrinsically disordered protein regions (IDPRs); Intrinsically disordered proteins (IDPs); Protein misfolding
    DOI:  https://doi.org/10.1016/j.ijbiomac.2022.10.120
  2. Mol Cell. 2022 Oct 17. pii: S1097-2765(22)00910-8. [Epub ahead of print]
      Many principles of bacterial gene regulation have been foundational to understanding mechanisms of eukaryotic transcription. However, stark structural and functional differences exist between eukaryotic and bacterial transcription factors that complicate inferring properties of the eukaryotic system from that of bacteria. Here, we review those differences, focusing on the impact of intrinsically disordered regions on the thermodynamic and kinetic parameters governing eukaryotic transcription factor interactions-both with other proteins and with chromatin. The prevalence of unstructured domains in eukaryotic transcription factors as well as their known impact on function call for more sophisticated knowledge of what mechanisms they support. Using the evidence available to date, we posit that intrinsically disordered regions are necessary for the complex and integrative functions of eukaryotic transcription factors and that only by understanding their rich biochemistry can we develop a deep molecular understanding of their regulatory mechanisms.
    Keywords:  gene regulation; intrinsically disordered region; transcription; transcription factor
    DOI:  https://doi.org/10.1016/j.molcel.2022.09.021
  3. Genes Dev. 2022 Oct 20.
      Intrinsically disordered protein regions (IDRs) have been implicated in diverse nuclear and cytoplasmic functions in eukaryotes, but their roles in bacteria are less clear. Here, we report that extracytoplasmic IDRs in Bacillus subtilis are required for cell wall homeostasis. The B. subtilis σI transcription factor is activated in response to envelope stress through regulated intramembrane proteolysis (RIP) of its membrane-anchored anti-σ factor, RsgI. Unlike canonical RIP pathways, we show that ectodomain (site-1) cleavage of RsgI is constitutive, but the two cleavage products remain stably associated, preventing intramembrane (site-2) proteolysis. The regulated step in this pathway is their dissociation, which is triggered by impaired cell wall synthesis and requires RsgI's extracytoplasmic IDR. Intriguingly, the major peptidoglycan polymerase PBP1 also contains an extracytoplasmic IDR, and we show that this region is important for its function. Disparate IDRs can replace the native IDRs on both RsgI and PBP1, arguing that these unstructured regions function similarly. Our data support a model in which the RsgI-σI signaling system and PBP1 represent complementary pathways to repair gaps in the PG meshwork. The IDR on RsgI senses these gaps and activates σI, while the IDR on PBP1 directs the synthase to these sites to fortify them.
    Keywords:  Notch; aGPCR; class A PBP; intrinsically disordered protein region; mechanotransduction; peptidoglycan; regulated intramembrane proteolysis (RIP)
    DOI:  https://doi.org/10.1101/gad.349895.122
  4. J Phys Chem B. 2022 Oct 17.
      The combination of deep learning and sequence data has transformed protein structure prediction and modeling, evidenced in the success of AlphaFold (AF). For this reason, many methods have been developed to take advantage of this success in areas where inaccurate structural modeling may limit computational predictiveness. For example, many methods have been developed to predict protein intrinsic disorder from sequence, including our Rosetta ResidueDisorder (RRD) approach. Intrinsically disordered regions in proteins are parts of the sequence that do not form ordered, folded structures under typical physiological conditions. In the original implementation of RRD, Rosetta ab initio models were generated, and disordered regions were predicted based on residue scores (disordered residues typically exist in regions of unfavorable scores). In this work, we show that by (i) replacing the ab initio modeling with AF (using the same scoring and disorder assignment approach) and (ii) updating the score function, the predictiveness improved significantly. Residues were better ranked by the order/disorder, evidenced by an improvement in receiver operating characteristic area-under-the-curve from 0.69 to 0.78 on a large (229 protein) and balanced data set (relatively even ordered versus disordered residues). Finally, the binary prediction accuracy also improved from 62% to 74% on the same data set. Our results show that the combined AF-RRD approach was as good as or better than all existing methods by these metrics (AF-RRD had the highest prediction accuracy).
    DOI:  https://doi.org/10.1021/acs.jpcb.2c05508
  5. Front Oncol. 2022 ;12 1024600
      The limited options for treating patients with drug-resistant cancers have emphasized the need to identify alternative treatment targets. Tumor cells have large super-enhancers (SEs) in the vicinity of important oncogenes for activation. The physical process of liquid-liquid phase separation (LLPS) contributes to the assembly of several membrane-less organelles in mammalian cells. Intrinsically disordered regions (IDRs) of proteins induce LLPS formation by developing condensates. It was discovered that key transcription factors (TFs) undergo LLPS in SEs. In addition, TFs play critical roles in the epigenetic and genetic regulation of cancer progression. Recently, we revealed the essential role of disease-specific TF collaboration changes in advanced prostate cancer (PC). OCT4 confers epigenetic changes by promoting complex formation with TFs, such as Forkhead box protein A1 (FOXA1), androgen receptor (AR) and Nuclear respiratory factor 1 (NRF1), inducing PC progression. It was demonstrated that TF collaboration through LLPS underlying transcriptional activation contributes to cancer aggressiveness and drug resistance. Moreover, the disruption of TF-mediated LLPS inhibited treatment-resistant PC tumor growth. Therefore, we propose that repression of TF collaborations involved in the LLPS of SEs could be a promising strategy for advanced cancer therapy. In this article, we summarize recent evidence highlighting the formation of LLPS on enhancers as a potent therapeutic target in advanced cancers.
    Keywords:  OCT4; androgen receptor; collaborative transcription factor; epigenome; liquid-liquid phase separation; nuclear analog; prostate cancer; super-enhancer
    DOI:  https://doi.org/10.3389/fonc.2022.1024600
  6. Front Mol Biosci. 2022 ;9 985022
      Intrinsically disordered proteins (IDPs) participate in many biological processes by interacting with other proteins, including the regulation of transcription, translation, and the cell cycle. With the increasing amount of disorder sequence data available, it is thus crucial to identify the IDP binding sites for functional annotation of these proteins. Over the decades, many computational approaches have been developed to predict protein-protein binding sites of IDP (IDP-PPIS) based on protein sequence information. Moreover, there are new IDP-PPIS predictors developed every year with the rapid development of artificial intelligence. It is thus necessary to provide an up-to-date overview of these methods in this field. In this paper, we collected 30 representative predictors published recently and summarized the databases, features and algorithms. We described the procedure how the features were generated based on public data and used for the prediction of IDP-PPIS, along with the methods to generate the feature representations. All the predictors were divided into three categories: scoring functions, machine learning-based prediction, and consensus approaches. For each category, we described the details of algorithms and their performances. Hopefully, our manuscript will not only provide a full picture of the status quo of IDP binding prediction, but also a guide for selecting different methods. More importantly, it will shed light on the inspirations for future development trends and principles.
    Keywords:  ML; intrinsically disordered protein (IDP); machine learning; protein functions; protein interaction sites prediction; protein sequence
    DOI:  https://doi.org/10.3389/fmolb.2022.985022
  7. Elife. 2022 Oct 19. pii: e79396. [Epub ahead of print]11
      How the cuticles of the roughly 4.5 million species of ecdysozoan animals are constructed is not well understood. Here, we systematically mine gene expression datasets to uncover the spatiotemporal blueprint for how the chitin-based pharyngeal cuticle of the nematode Caenorhabditis elegans is built. We demonstrate that the blueprint correctly predicts expression patterns and functional relevance to cuticle development. We find that as larvae prepare to molt, catabolic enzymes are upregulated and the genes that encode chitin synthase, chitin cross-linkers, and homologs of amyloid regulators subsequently peak in expression. 48% of the gene products secreted during the molt are predicted to be intrinsically disordered proteins (IDPs), many of which belong to four distinct families whose transcripts are expressed in overlapping waves. These include the IDPAs, IDPBs, and IDPCs, which are introduced for the first time here. All four families have sequence properties that drive phase separation and we demonstrate phase-separation for one exemplar in vitro. This systematic analysis represents the first blueprint for cuticle construction and highlights the massive contribution that phase-separating materials make to the structure.
    Keywords:  C. elegans; developmental biology
    DOI:  https://doi.org/10.7554/eLife.79396
  8. Bioessays. 2022 Oct 17. e2200145
      Cis-regulatory elements govern gene expression programs to determine cell identity during development. Recently, the possibility that multiple enhancers are orchestrated in clusters of enhancers has been suggested. How these elements are arranged in the 3D space to control the activation of a specific promoter remains unclear. Our recent work revealed that the TGFβ pathway drives the assembly of enhancer clusters and precise gene activation during neurogenesis. We discovered that the TGFβ pathway coactivator JMJD3 was essential in maintaining these structures in the 3D space. To do that, JMJD3 required an intrinsically disordered region involved in forming phase-separated biomolecular condensates found in the enhancer clusters. Our data support the existence of a relationship between 3D-conformation of the chromatin, biomolecular condensates, and TGFβ-driven response during mammalian neurogenesis. In this review, we discuss how signaling (TGFβ), epigenetics (JMJD3), and biochemical properties (biomolecular condensates nucleation) are coordinated to modulate the genome structure to guarantee proper neural development. Moreover, we comment on the potential underlying mechanisms and implications of the enhancer-mediated regulation. Finally, we point out the knowledge gaps that still need to be addressed.
    Keywords:  3D genome structure; JMJD3; TGFβ; biomolecular condensates; enhancer cluster; neurogenesis; transcription regulation
    DOI:  https://doi.org/10.1002/bies.202200145
  9. Comput Struct Biotechnol J. 2022 ;20 5516-5523
      Low complexity regions (LCRs) differ in amino acid composition from the background provided by the corresponding proteomes. The simplest LCRs are homorepeats (or polyX), regions composed of mostly-one amino acid type. Extensive research has been done to characterize homorepeats, and their taxonomic, functional and structural features depend on the amino acid type and sequence context. From them, the next step towards the study of LCRs are the regions composed of two types of amino acids, which we call polyXY. We classify polyXY in three categories based on the arrangement of the two amino acid types 'X' and 'Y': direpeats (e.g. 'XYXYXY'), joined (e.g. 'XXXYYY') and shuffled (e.g. 'XYYXXY'). We developed a script to search for polyXY, and located them in a comprehensive set of 20,340 reference proteomes. These results are available in a dedicated web server called XYs, in which the user can also submit their own protein datasets to detect polyXY. We studied the distribution of polyXY types by amino acid pair XY and category, and show that polyXY in Eukaryota are mainly located within intrinsically disordered regions. Our study provides a first step towards the characterization of polyXY as protein motifs.
    Keywords:  Linear motifs; Low complexity regions; Protein sequence analysis; polyXY
    DOI:  https://doi.org/10.1016/j.csbj.2022.09.011
  10. Int J Biol Macromol. 2022 Oct 14. pii: S0141-8130(22)02307-8. [Epub ahead of print]
      Metal ions present in cellular microenvironment have been implicated as drivers of aggregation of amyloid forming proteins. Zinc (Zn2+) ions have been reported to directly interact with α-synuclein (AS), a causative agent of Parkinson's disease and other neurodegenerative diseases, and promote its aggregation. AS is a small intrinsically disordered protein (IDP) i.e., understanding molecular factors that drive its misfolding and aggregation has been challenging since methods used routinely to study protein structure are not effective for IDPs. Here, we report the atomic details of Zn2+ binding to AS at physiologically relevant conditions using proton-less NMR techniques that can be applied to highly dynamic systems like IDPs. We also examined how human serum albumin (HSA), the most abundant protein in human blood, binds to AS and whether Zn2+ and/or ionic strength affect this. We conclude that Zn2+ enhances the anti-aggregation chaperoning role of HSA that relies on protecting the hydrophobic N-terminal and NAC regions of AS, rather than polar negatively charged C-terminus. This suggested a previously undocumented role of Zn2+ in HSA function and AS aggregation.
    Keywords:  Aggregation; Human serum albumin; Physiological conditions; Proton-less NMR; Zinc ions; α-Synuclein
    DOI:  https://doi.org/10.1016/j.ijbiomac.2022.10.066
  11. J Mater Chem B. 2022 Oct 21.
      Liquid-liquid phase separation (LLPS) of biomolecules inspires the construction of protocells and drives the formation of cellular membraneless organelles. The resulting biomolecular condensates featuring dynamic assembly, disassembly, and phase transition play significant roles in a series of biological processes, including RNA metabolism, DNA damage response, signal transduction and neurodegenerative disease. Intensive investigations have been conducted for understanding and manipulating intracellular phase-separated disease-related proteins (e.g., FUS, tau and TDP-43). Herein, we review current studies on the regulation strategies of intracellular LLPS focusing on FUS, which are categorized into physical stimuli, biochemical modulators, and protein structural modifications, with summarized molecular mechanisms. This review is expected to provide a sketch of the modulation of FUS LLPS with its pros and cons, and an outlook for the potential clinical treatments of neurodegenerative diseases.
    DOI:  https://doi.org/10.1039/d2tb01688e
  12. Essays Biochem. 2022 Oct 17. pii: EBC20220066. [Epub ahead of print]
      The aggregation and misfolding of the neuronal microtubule-associated protein tau is closely linked to the pathology of Alzheimer's disease and several other neurodegenerative diseases. Recent evidence suggest that tau undergoes liquid-liquid phase separation in vitro and forms or associates with membrane-less organelles in cells. Biomolecular condensation driven by phase separation can influence the biological activities of tau including its ability to polymerize tubulin into microtubules. In addition, the high concentrations that tau can reach in biomolecular condensates provide a mechanism to promote its aggregation and the formation of amyloid fibrils potentially contributing to the pathology of different tauopathies. Here, the authors discuss the role of tau phase separation in physiology and disease.
    Keywords:  Alzheimer's disease; liquid-liquid phase separation; post-translational modification; tau protein
    DOI:  https://doi.org/10.1042/EBC20220066
  13. Oxid Med Cell Longev. 2022 ;2022 7165387
      The pathological features of PDD are represented by dopaminergic neuronal death and intracellular α-synuclein (α-syn) aggregation. The interaction of iron accumulation with α-syn and tau was further explored as an essential pathological mechanism of PDD. However, the links and mechanisms between these factors remain unclear. Studies have shown that the occurrence and development of neurodegenerative diseases such as PDD are closely related to the separation of abnormal phases. Substances such as proteins can form droplets through liquid-liquid phase separation (LLPS) under normal physiological conditions and even undergo further liquid-solid phase transitions to form solid aggregates under disease or regulatory disorders, leading to pathological phenomena. By analyzing the existing literature, we propose that LLPS is the crucial mechanism causing abnormal accumulation of α-syn, tau, and other proteins in PDD, and its interaction with iron metabolism disorder is the key factor driving ferroptosis in PDD. Therefore, we believe that LLPS can serve as one of the means to explain the pathological mechanism of PDD. Determining the significance of LLPS in neurodegenerative diseases such as PDD will stimulate interest in research into treatments based on interference with abnormal LLPS.
    DOI:  https://doi.org/10.1155/2022/7165387
  14. Nat Commun. 2022 Oct 18. 13(1): 6172
      The permeability barrier of nuclear pore complexes (NPCs) controls nucleocytoplasmic transport. It retains inert macromolecules but allows facilitated passage of nuclear transport receptors that shuttle cargoes into or out of nuclei. The barrier can be described as a condensed phase assembled from cohesive FG repeat domains, including foremost the charge-depleted FG domain of Nup98. We found that Nup98 FG domains show an LCST-type phase separation, and we provide comprehensive and orthogonal experimental datasets for a quantitative description of this behaviour. A derived thermodynamic model correlates saturation concentration with repeat number, temperature, and ionic strength. It allows estimating the enthalpy, entropy, and ΔG (0.2 kJ/mol, 0.1 kB·T) contributions per repeat to phase separation and inter-repeat cohesion. While changing the cohesion strength strongly impacts the strictness of barrier, these numbers provide boundary conditions for in-depth modelling not only of barrier assembly but also of NPC passage.
    DOI:  https://doi.org/10.1038/s41467-022-33697-9
  15. Bioessays. 2022 Oct 17. e2200181
      The transactivation response-DNA binding protein of 43 kDa (TDP-43) is an aggregation-prone nucleic acid-binding protein linked to the etiology of Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Lobar Degeneration (FTLD). These conditions feature the accumulation of insoluble TDP-43 aggregates in the neuronal cytoplasm that lead to cell death. The dynamics between cytoplasmic and nuclear TDP-43 are altered in the disease state where TDP-43 mislocalizes to the cytoplasm, disrupting Nuclear Pore Complexes (NPCs), and ultimately forming large fibrils stabilized by the C-terminal prion-like domain. Here, we review three emerging and poorly understood aspects of TDP-43 biology linked to its aggregation. First, how post-translational modifications in the proximity of TDP-43 N-terminal domain (NTD) promote aggregation. Second, how TDP-43 engages FG-nucleoporins in the NPC, disrupting the pore permeability and function. Third, how the importin α/β heterodimer prevents TDP-43 aggregation, serving both as a nuclear import transporter and a cytoplasmic chaperone.
    Keywords:  FG-nucleoporins; NTD; TDP-43; neurodegeneration; protein aggregation;  importin α/β
    DOI:  https://doi.org/10.1002/bies.202200181
  16. J Mol Biol. 2022 Oct 18. pii: S0022-2836(22)00479-X. [Epub ahead of print] 167859
      Fibrillar aggregates of the α-synuclein (αS) protein are the hallmark of Parkinson's Disease and related neurodegenerative disorders. Characterization of the effects of mutations and post-translational modifications (PTMs) on the αS aggregation rate can provide insight into the mechanism of fibril formation, which remains elusive in spite of intense study. A comprehensive collection (375 examples) of mutant and PTM aggregation rate data measured using the fluorescent probe thioflavin T is presented, as well as a summary of the effects of fluorescent labeling on αS aggregation (20 examples). A curated set of 131 single mutant de novo aggregation experiments are normalized to wild type controls and analyzed in terms of structural data for the monomer and fibrillar forms of αS. These tabulated data serve as a resource to the community to help in interpretation of aggregation experiments and to potentially be used as inputs for computational models of aggregation.
    Keywords:  Parkinson’s Disease; amyloid; fibril; neurodegenerative disorder; thioflavin T
    DOI:  https://doi.org/10.1016/j.jmb.2022.167859
  17. Mol Psychiatry. 2022 Oct 18.
      Fyn is a Src kinase that controls critical signalling cascades and has been implicated in learning and memory. Postsynaptic enrichment of Fyn underpins synaptotoxicity in dementias such as Alzheimer's disease and frontotemporal lobar degeneration with Tau pathology (FTLD-Tau). The FLTD P301L mutant Tau is associated with a higher propensity to undergo liquid-liquid phase separation (LLPS) and form biomolecular condensates. Expression of P301L mutant Tau promotes aberrant trapping of Fyn in nanoclusters within hippocampal dendrites by an unknown mechanism. Here, we used single-particle tracking photoactivated localisation microscopy to demonstrate that the opening of Fyn into its primed conformation promotes its nanoclustering in dendrites leading to increased Fyn/ERK/S6 downstream signalling. Preventing the auto-inhibitory closed conformation of Fyn through phospho-inhibition or through perturbation of its SH3 domain increased Fyn's nanoscale trapping, whereas inhibition of the catalytic domain had no impact. By combining pharmacological and genetic approaches, we demonstrate that P301L Tau enhanced both Fyn nanoclustering and Fyn/ERK/S6 signalling via its ability to form biomolecular condensates. Together, our findings demonstrate that Fyn alternates between a closed and an open conformation, the latter being enzymatically active and clustered. Furthermore, pathogenic immobilisation of Fyn relies on the ability of P301L Tau to form biomolecular condensates, thus highlighting the critical importance of LLPS in controlling nanoclustering and downstream intracellular signalling events.
    DOI:  https://doi.org/10.1038/s41380-022-01825-y
  18. Exp Neurol. 2022 Oct 12. pii: S0014-4886(22)00276-X. [Epub ahead of print] 114251
      Looking at the puzzle that depicts the molecular determinants in neurodegeneration, many pieces are lacking and multiple interconnections among key proteins and intracellular pathways still remain unclear. Here we focus on the concerted action of α-synuclein and the microtubule cytoskeleton, whose interplay, indeed, is emerging but remains largely unexplored in both its physiology and pathology. α-Synuclein is a key protein involved in neurodegeneration, underlying those diseases termed synucleinopathies. Its propensity to interact with other proteins and structures renders the identification of neuronal death trigger extremely difficult. Conversely, the unbalance of microtubule cytoskeleton in terms of structure, dynamics and function is emerging as a point of convergence in neurodegeneration. Interestingly, α-synuclein and microtubules have been shown to interact and mediate cross-talks with other intracellular structures. This is supported by an increasing amount of evidence ranging from their direct interaction to the engagement of in-common partners and culminating with their respective impact on microtubule-dependent neuronal functions. Last, but not least, it is becoming even more clear that α-synuclein and tubulin work synergically towards pathological aggregation, ultimately resulting in neurodegeneration. In this respect, we supply a novel perspective towards the understanding of α-synuclein biology and, most importantly, of the link between α-synuclein with microtubule cytoskeleton and its impact for neurodegeneration and future development of novel therapeutic strategies.
    Keywords:  Microtubule; Neurodegeneration; Synucleinopathies; Tubulin; α-Synuclein
    DOI:  https://doi.org/10.1016/j.expneurol.2022.114251