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1.
Adv Sci (Weinh) ; 10(34): e2304891, 2023 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-37870218

RESUMO

Innate immune adaptor proteins are critical components of the innate immune system that propagate pro-inflammatory responses from their upstream receptors, and lead to pathogen clearance from the host. Bacterial pathogens have developed strategies to survive inside host cells without triggering the innate immune surveillance in ways that are still not fully understood. Here, it is reported that Pseudomonas aeruginosa induces its quorum sensing mechanism after macrophage engulfment. Further investigation of its secretome identified a quorum sensing regulated product, LasB, is responsible for innate immune suppression depending on the MyD88-mediated signaling. Moreover, it is showed that this specific type of pathogen-mediated innate immune suppression is due to the enzymatic digestion of the death domains of the innate immune adaptors, mainly MyD88, and attributed to LasB's large substrate binding groove. Lastly, it is demonstrated that the secretion of LasB from P. aeruginosa directly contributed to MyD88 degradation within macrophages. Hence, it is discovered an example of bacterial quorum sensing-regulated cellular innate immune suppression by direct cleavage of immune adaptors.


Assuntos
Peptídeo Hidrolases , Percepção de Quorum , Peptídeo Hidrolases/metabolismo , Domínio de Morte , Fator 88 de Diferenciação Mieloide/metabolismo , Endopeptidases/metabolismo , Imunidade Inata
2.
Int J Mol Sci ; 22(19)2021 Sep 25.
Artigo em Inglês | MEDLINE | ID: mdl-34638680

RESUMO

Medium-chain triglycerides (MCTs) are an emerging choice to treat neurodegenerative disorders such as Alzheimer's disease. They are triesters of glycerol and three medium-chain fatty acids, such as capric (C8) and caprylic (C10) acids. The availability of C8-C10 methyl esters (C8-C10 ME) from vegetable oil processes has presented an opportunity to use methyl esters as raw materials for the synthesis of MCTs. However, there are few reports on enzymes that can efficiently hydrolyse C8-C10 ME to industrial specifications. Here, we report the discovery and identification of a novel lipase from Lasiodiplodia theobromae fungus (LTL1), which hydrolyses C8-C10 ME efficiently. LTL1 can perform hydrolysis over pH ranges from 3.0 to 9.0 and maintain thermotolerance up to 70 °C. It has high selectivity for monoesters over triesters and displays higher activity over commercially available lipases for C8-C10 ME to achieve 96.17% hydrolysis within 31 h. Structural analysis by protein X-ray crystallography revealed LTL1's well-conserved lipase core domain, together with a partially resolved N-terminal subdomain and an inserted loop, which may suggest its hydrolytic preference for monoesters. In conclusion, our results suggest that LTL1 provides a tractable route towards to production of C8-C10 fatty acids from methyl esters for the synthesis of MCTs.


Assuntos
Ascomicetos/metabolismo , Ésteres/metabolismo , Lipase/metabolismo , Sequência de Aminoácidos , Ácidos Graxos/metabolismo , Glicerol/metabolismo , Hidrólise , Óleos de Plantas/metabolismo , Triglicerídeos/metabolismo
3.
Nat Commun ; 12(1): 4800, 2021 08 20.
Artigo em Inglês | MEDLINE | ID: mdl-34417450

RESUMO

Histone lysine methylations have primarily been linked to selective recruitment of reader or effector proteins that subsequently modify chromatin regions and mediate genome functions. Here, we describe a divergent role for histone H4 lysine 20 mono-methylation (H4K20me1) and demonstrate that it directly facilitates chromatin openness and accessibility by disrupting chromatin folding. Thus, accumulation of H4K20me1 demarcates highly accessible chromatin at genes, and this is maintained throughout the cell cycle. In vitro, H4K20me1-containing nucleosomal arrays with nucleosome repeat lengths (NRL) of 187 and 197 are less compact than unmethylated (H4K20me0) or trimethylated (H4K20me3) arrays. Concordantly, and in contrast to trimethylated and unmethylated tails, solid-state NMR data shows that H4K20 mono-methylation changes the H4 conformational state and leads to more dynamic histone H4-tails. Notably, the increased chromatin accessibility mediated by H4K20me1 facilitates gene expression, particularly of housekeeping genes. Altogether, we show how the methylation state of a single histone H4 residue operates as a focal point in chromatin structure control. While H4K20me1 directly promotes chromatin openness at highly transcribed genes, it also serves as a stepping-stone for H4K20me3-dependent chromatin compaction.


Assuntos
Cromatina/metabolismo , Genes Essenciais , Histonas/metabolismo , Lisina/metabolismo , Transcrição Gênica , Sequência de Aminoácidos , Animais , Ciclo Celular/genética , Linhagem Celular , Histona-Lisina N-Metiltransferase/metabolismo , Histonas/química , Humanos , Espectroscopia de Ressonância Magnética , Metilação , Camundongos , Modelos Biológicos , Nucleossomos/metabolismo , Conformação Proteica
4.
Chem Commun (Camb) ; 56(7): 1082-1084, 2020 Jan 23.
Artigo em Inglês | MEDLINE | ID: mdl-31894763

RESUMO

G-quadruplexes (G4) are non-canonical nucleic acid structures with important implications in biology. Based on an α-helical fragment of the RHAU helicase that displays high specificity for parallel-stranded G-quadrplexes, herein we demonstrate its head-to-tail cyclization by a high-efficiency ligase. The cyclic peptide exhibits superior stability and binding affinity to a G-quadruplex, and can serve as an excellent investigational tool for chemical biology applications.


Assuntos
RNA Helicases DEAD-box/metabolismo , DNA/metabolismo , Quadruplex G , Fragmentos de Peptídeos/metabolismo , Peptídeos Cíclicos/metabolismo , Células A549 , Ciclização , RNA Helicases DEAD-box/química , DNA/genética , Humanos , Oldenlandia/enzimologia , Fragmentos de Peptídeos/química , Peptídeo Sintases/química , Peptídeos Cíclicos/síntese química , Ligação Proteica , Estabilidade Proteica
5.
Nat Commun ; 9(1): 4993, 2018 11 26.
Artigo em Inglês | MEDLINE | ID: mdl-30478312

RESUMO

Signals arising from bacterial infections are detected by pathogen recognition receptors (PRRs) and are transduced by specialized adapter proteins in mammalian cells. The Receptor-interacting-serine/threonine-protein kinase 2 (RIPK2 or RIP2) is such an adapter protein that is critical for signal propagation of the Nucleotide-binding-oligomerization-domain-containing proteins 1/2 (NOD1 and NOD2). Dysregulation of this signaling pathway leads to defects in bacterial detection and in some cases autoimmune diseases. Here, we show that the Caspase-activation-and-recruitment-domain (CARD) of RIP2 (RIP2-CARD) forms oligomeric structures upon stimulation by either NOD1-CARD or NOD2-2CARD. We reconstitute this complex, termed the RIPosome in vitro and solve the cryo-EM filament structure of the active RIP2-CARD complex at 4.1 Å resolution. The structure suggests potential mechanisms by which CARD domains from NOD1 and NOD2 initiate the oligomerization process of RIP2-CARD. Together with structure guided mutagenesis experiments at the CARD-CARD interfaces, we demonstrate molecular mechanisms how RIP2 is activated and self-propagating such signal.


Assuntos
Proteína Serina-Treonina Quinase 2 de Interação com Receptor/química , Proteína Serina-Treonina Quinase 2 de Interação com Receptor/metabolismo , Transdução de Sinais , Sequência de Aminoácidos , Proteínas Adaptadoras de Sinalização CARD/química , Proteínas Adaptadoras de Sinalização CARD/metabolismo , Microscopia Crioeletrônica , Células HEK293 , Humanos , Modelos Moleculares , Ligação Proteica , Domínios Proteicos , Multimerização Proteica , Proteína Serina-Treonina Quinase 2 de Interação com Receptor/ultraestrutura , Proteínas Recombinantes/metabolismo , Relação Estrutura-Atividade
6.
Org Lett ; 20(21): 6691-6694, 2018 11 02.
Artigo em Inglês | MEDLINE | ID: mdl-30350676

RESUMO

By facilitating formation of the acyl-enzyme intermediate, peptide thioesters can largely promote subtiligase-catalyzed ligation reactions over their ester counterparts. This offers a significant addition to the repertoire of enzymatic methods for protein chemical synthesis and modification.

7.
Sci Rep ; 8(1): 1155, 2018 01 18.
Artigo em Inglês | MEDLINE | ID: mdl-29348452

RESUMO

The threat of antibiotic resistant bacteria has called for alternative antimicrobial strategies that would mitigate the increase of classical resistance mechanism. Many bacteria employ quorum sensing (QS) to govern the production of virulence factors and formation of drug-resistant biofilms. Targeting the mechanism of QS has proven to be a functional alternative to conventional antibiotic control of infections. However, the presence of multiple QS systems in individual bacterial species poses a challenge to this approach. Quorum sensing inhibitors (QSI) and quorum quenching enzymes (QQE) have been both investigated for their QS interfering capabilities. Here, we first simulated the combination effect of QQE and QSI in blocking bacterial QS. The effect was next validated by experiments using AiiA as QQE and G1 as QSI on Pseudomonas aeruginosa LasR/I and RhlR/I QS circuits. Combination of QQE and QSI almost completely blocked the P. aeruginosa las and rhl QS systems. Our findings provide a potential chemical biology application strategy for bacterial QS disruption.


Assuntos
Antibacterianos/farmacologia , Proteínas de Bactérias/farmacologia , Biofilmes/efeitos dos fármacos , Regulação Bacteriana da Expressão Gênica/efeitos dos fármacos , Metaloendopeptidases/farmacologia , Pseudomonas aeruginosa/efeitos dos fármacos , Percepção de Quorum/efeitos dos fármacos , Proteínas de Bactérias/antagonistas & inibidores , Proteínas de Bactérias/biossíntese , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Biofilmes/crescimento & desenvolvimento , Combinação de Medicamentos , Sinergismo Farmacológico , Ligases/antagonistas & inibidores , Ligases/genética , Ligases/metabolismo , Metaloendopeptidases/biossíntese , Metaloendopeptidases/genética , Testes de Sensibilidade Microbiana , Pseudomonas aeruginosa/genética , Pseudomonas aeruginosa/metabolismo , Pirimidinonas/farmacologia , Percepção de Quorum/genética , Proteínas Recombinantes/biossíntese , Proteínas Recombinantes/genética , Proteínas Recombinantes/farmacologia , Transativadores/antagonistas & inibidores , Transativadores/genética , Transativadores/metabolismo , Fatores de Transcrição/antagonistas & inibidores , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Triazóis/farmacologia
8.
J Mol Biol ; 429(13): 2075-2092, 2017 06 30.
Artigo em Inglês | MEDLINE | ID: mdl-28322915

RESUMO

Chromatin folding and dynamics are critically dependent on nucleosome-nucleosome interactions with important contributions from internucleosome binding of the histone H4 N-terminal tail K16-R23 domain to the surface of the H2A/H2B dimer. The H4 Lys16 plays a pivotal role in this regard. Using in vitro reconstituted 12-mer nucleosome arrays, we have investigated the mechanism of the H4 N-terminal tail in maintaining nucleosome-nucleosome stacking and mediating intra- and inter-array chromatin compaction, with emphasis on the role of K16 and the positive charge region, R17-R23. Analytical ultracentrifugation sedimentation velocity experiments and precipitation assays were employed to analyze effects on chromatin folding and self-association, respectively. Effects on chromatin folding caused by various mutations and modifications at position K16 in the H4 histone were studied. Additionally, using charge-quenching mutations, we characterized the importance of the interaction of the residues within the H4 positive charge region R17-R23 with the H2A acidic patch of the adjacent nucleosome. Furthermore, crosslinking experiments were conducted to establish the proximity of the basic tail region to the acidic patch. Our data indicate that the positive charge and length of the side chain of H4 K16 are important for its access to the adjacent nucleosome in the process of nucleosome-nucleosome stacking and array folding. The location and orientation of the H4 R17-R23 domain on the H2A/H2B dimer surface of the neighboring nucleosome core particle (NCP) in the compacted chromatin fiber were established. The dominance of electrostatic interactions in maintaining intra-array interaction was demonstrated.


Assuntos
Cromatina/metabolismo , Histonas/química , Histonas/metabolismo , Nucleossomos/metabolismo , Animais , Precipitação Química , Modelos Moleculares , Ultracentrifugação , Xenopus laevis
9.
J Am Chem Soc ; 139(15): 5351-5358, 2017 04 19.
Artigo em Inglês | MEDLINE | ID: mdl-28199119

RESUMO

Breaking and forming peptidyl bonds are fundamental biochemical reactions in protein chemistry. Unlike proteases that are abundantly available, fast-acting ligases are rare. OaAEP1 is an enzyme isolated from the cyclotide-producing plant oldenlandia affinis that displayed weak peptide cyclase activity, despite having a similar structural fold with other asparaginyl endopeptidases (AEP). Here we report the first atomic structure of OaAEP1, at a resolution of 2.56 Å, in its preactivation form. Our structure and biochemical analysis of this enzyme reveals its activation mechanism as well as structural features important for its ligation activity. Importantly, through structure-based mutagenesis of OaAEP1, we obtained an ultrafast variant having hundreds of times faster catalytic kinetics, capable of ligating well-folded protein substrates using only a submicromolar concentration of enzyme. In contrast, the protein-protein ligation activity in the original wild-type OaAEP1 enzyme described previously is extremely weak. Thus, the structure-based engineering of OaAEP1 described here provides a unique and novel recombinant tool that can now be used to conduct various protein labeling and modifications that were extremely challenging before.


Assuntos
Biocatálise , Ligases/metabolismo , Engenharia de Proteínas , Ligases/química , Ligases/isolamento & purificação , Modelos Moleculares , Oldenlandia/enzimologia , Proteínas Recombinantes/química , Proteínas Recombinantes/isolamento & purificação , Proteínas Recombinantes/metabolismo
10.
Org Lett ; 18(11): 2696-9, 2016 06 03.
Artigo em Inglês | MEDLINE | ID: mdl-27218276

RESUMO

Palladium-catalyzed acetoxylation of the primary γ-C(sp(3))-H bonds in the amino acids Val, Thr, and Ile was achieved using a newly discovered 5-methylisoxazole-3-carboxamide directing group. The γ-acetoxylated α-amino acid derivatives could be easily converted to γ-mercapto amino acids, which are useful for native chemical ligation (NCL). The first application of NCL at isoleucine in the semisynthesis of a Xenopus histone H3 protein was also demonstrated.


Assuntos
Aminoácidos/síntese química , Isoxazóis/química , Paládio/química , Sequência de Aminoácidos , Catálise , Histonas/química , Ligação de Hidrogênio , Estrutura Molecular , Proteínas de Xenopus/química
11.
Biophys J ; 110(8): 1720-1731, 2016 04 26.
Artigo em Inglês | MEDLINE | ID: mdl-27119633

RESUMO

The nucleosome core particle (NCP) is the basic building block of chromatin. Nucleosome-nucleosome interactions are instrumental in chromatin compaction, and understanding NCP self-assembly is important for understanding chromatin structure and dynamics. Recombinant NCPs aggregated by multivalent cations form various ordered phases that can be studied by x-ray diffraction (small-angle x-ray scattering). In this work, the effects on the supramolecular structure of aggregated NCPs due to lysine histone H4 tail acetylations, histone H2A mutations (neutralizing the acidic patch of the histone octamer), and the removal of histone tails were investigated. The formation of ordered mainly hexagonal columnar NCP phases is in agreement with earlier studies; however, the highly homogeneous recombinant NCP systems used in this work display a more compact packing. The long-range order of the NCP columnar phase was found to be abolished or reduced by acetylation of the H4 tails, acidic patch neutralization, and removal of the H3 and H2B tails. Loss of nucleosome stacking upon removal of the H3 tails in combination with other tails was observed. In the absence of the H2A tails, the formation of an unknown highly ordered phase was observed.


Assuntos
Histonas/química , Histonas/metabolismo , Nucleossomos/metabolismo , Acetilação , Animais , Histonas/genética , Mutação , Domínios Proteicos , Xenopus laevis
13.
Top Curr Chem ; 362: 89-106, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-25860252

RESUMO

In eukaryotic cells, many proteins undergo extensive post-translational modifications (PTMs) such as methylation, acetylation, phosphorylation, glycosylation, and ubiquitination. Among these, ubiquitination is a particularly interesting PTM from both structural and functional viewpoints. In ubiquitination, the C-terminal carboxyl group of the small ubiquitin protein is attached to the ε-amine of a lysine residue of a substrate protein through an isopeptide bond. Ubiquitination has been shown to be involved in the regulation of many cellular processes including protein degradation and gene expression. And dysfunction of these processes is implicated in many human diseases. Despite many years of intensive research, a large number of protein ubquitination events remain poorly characterized. The challenge lies with the tremendous difficulties in isolating homogeneously modified proteins from biological samples for structural and functional studies. Enzymatic ubiquitination in vitro often has limited practical value due to the large number of substrate-specific E3 ligases and the difficulties in identifying or isolating these enzymes. Chemical approaches to the preparation of ubiquitinated proteins provide a powerful solution, and the development of such approaches has been the subject of intense research by many research laboratories. This review summarizes the methodological developments of protein chemical ubiquitination in recent years.


Assuntos
Proteínas/química , Conformação Proteica , Engenharia de Proteínas , Processamento de Proteína Pós-Traducional , Ubiquitina , Ubiquitinação
14.
Chem Commun (Camb) ; 50(59): 7971-4, 2014 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-24915456

RESUMO

A robust chemical ubiquitination method was developed. The method employed a genetically incorporated azidonorleucine as an orthogonal lysine precursor for the installation of a Gly residue bearing an Nα-auxiliary which mediated the ligation between ubiquitin(1-75)-thioester and the target protein. To demonstrate our methodology, a model protein, K48-linked diubiquitin, was synthesized with an overall yield of 35%.


Assuntos
Azidas/química , Norleucina/análogos & derivados , Ubiquitinas/química , Estrutura Molecular , Norleucina/química , Ubiquitinação , Ubiquitinas/síntese química
15.
PLoS One ; 9(2): e88411, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-24516652

RESUMO

ISWI is the catalytic subunit of several ATP-dependent chromatin remodelling factors that catalyse the sliding of nucleosomes along DNA and thereby endow chromatin with structural flexibility. Full activity of ISWI requires residues of a basic patch of amino acids in the N-terminal 'tail' of histone H4. Previous studies employing oligopeptides and mononucleosomes suggested that acetylation of the H4 tail at lysine 16 (H4K16) within the basic patch may inhibit the activity of ISWI. On the other hand, the acetylation of H4K16 is known to decompact chromatin fibres. Conceivably, decompaction may enhance the accessibility of nucleosomal DNA and the H4 tail for ISWI interactions. Such an effect can only be evaluated at the level of nucleosome arrays. We probed the influence of H4K16 acetylation on the ATPase and nucleosome sliding activity of Drosophila ISWI in the context of defined, in vitro reconstituted chromatin fibres with physiological nucleosome spacing and linker histone content. Contrary to widespread expectations, the acetylation did not inhibit ISWI activity, but rather stimulated ISWI remodelling under certain conditions. Therefore, the effect of H4K16 acetylation on ISWI remodelling depends on the precise nature of the substrate.


Assuntos
Adenosina Trifosfatases/metabolismo , Montagem e Desmontagem da Cromatina , Cromatina/metabolismo , Histonas/metabolismo , Lisina/metabolismo , Fatores de Transcrição/metabolismo , Acetilação , Animais , Drosophila melanogaster/metabolismo , Complexos Multiproteicos/metabolismo , Nucleossomos/metabolismo
16.
Org Lett ; 14(1): 374-7, 2012 Jan 06.
Artigo em Inglês | MEDLINE | ID: mdl-22176025

RESUMO

A novel N- to C-terminus sequential chemical ligation approach has been developed for protein synthesis. Key to this strategy is the relative stability of the N,N-bis(2-mercaptoethyl)amide (BMEA) to the conventional conditions of native chemical ligation. We have also found a new thiol additive for the BMEA-mediated ligation reaction. The usefulness of this approach was demonstrated in the syntheses of a medium-sized peptide and ubiquitin.


Assuntos
Amidas/química , Carbono/química , Nitrogênio/química , Peptídeos/química , Estrutura Molecular , Ubiquitina/química
17.
J Mol Biol ; 414(5): 749-64, 2011 Dec 16.
Artigo em Inglês | MEDLINE | ID: mdl-22051513

RESUMO

Nucleosome-nucleosome interaction plays a fundamental role in chromatin folding and self-association. The cation-induced condensation of nucleosome core particles (NCPs) displays properties similar to those of chromatin fibers, with important contributions from the N-terminal histone tails. We study the self-association induced by addition of cations [Mg(2+), Ca(2+), cobalt(III)hexammine(3+), spermidine(3+) and spermine(4)(+)] for NCPs reconstituted with wild-type unmodified histones and with globular tailless histones and for NCPs with the H4 histone tail having lysine (K) acetylations or lysine-to-glutamine mutations at positions K5, K8, K12 and K16. In addition, the histone construct with the single H4K16 acetylation was investigated. Acetylated histones were prepared by a semisynthetic native chemical ligation method. The aggregation behavior of NCPs shows a general cation-dependent behavior similar to that of the self-association of nucleosome arrays. Unlike nucleosome array self-association, NCP aggregation is sensitive to position and nature of the H4 tail modification. The tetra-acetylation in the H4 tail significantly weakens the nucleosome-nucleosome interaction, while the H4 K→Q tetra-mutation displays a more modest effect. The single H4K16 acetylation also weakens the self-association of NCPs, which reflects the specific role of H4K16 in the nucleosome-nucleosome stacking. Tailless NCPs can aggregate in the presence of oligocations, which indicates that attraction also occurs by tail-independent nucleosome-nucleosome stacking and DNA-DNA attraction in the presence of cations. The experimental data were compared with the results of coarse-grained computer modeling for NCP solutions with explicit presence of mobile ions.


Assuntos
Histonas/química , Nucleossomos/química , Acetilação , Animais , Cálcio/química , Cobalto/química , Simulação por Computador , Histonas/genética , Histonas/metabolismo , Humanos , Magnésio/química , Mutação , Nucleossomos/metabolismo , Ligação Proteica , Espermidina/química , Espermina/química , Proteínas de Xenopus , Xenopus laevis
19.
Cell ; 146(4): 607-20, 2011 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-21854985

RESUMO

Previous experiments suggest a connection between the N-alpha-acetylation of proteins and sensitivity of cells to apoptotic signals. Here, we describe a biochemical assay to detect the acetylation status of proteins and demonstrate that protein N-alpha-acetylation is regulated by the availability of acetyl-CoA. Because the antiapoptotic protein Bcl-xL is known to influence mitochondrial metabolism, we reasoned that Bcl-xL may provide a link between protein N-alpha-acetylation and apoptosis. Indeed, Bcl-xL overexpression leads to a reduction in levels of acetyl-CoA and N-alpha-acetylated proteins in the cell. This effect is independent of Bax and Bak, the known binding partners of Bcl-xL. Increasing cellular levels of acetyl-CoA by addition of acetate or citrate restores protein N-alpha-acetylation in Bcl-xL-expressing cells and confers sensitivity to apoptotic stimuli. We propose that acetyl-CoA serves as a signaling molecule that couples apoptotic sensitivity to metabolism by regulating protein N-alpha-acetylation.


Assuntos
Sobrevivência Celular , Proteínas/metabolismo , Proteína bcl-X/metabolismo , Acetilação , Animais , Apoptose , Caspase 2/metabolismo , Linhagem Celular , Embrião de Mamíferos/citologia , Técnicas de Inativação de Genes , Células HeLa , Humanos , Células Jurkat , Camundongos , Processamento de Proteína Pós-Traducional
20.
Nucleic Acids Res ; 39(5): 1680-91, 2011 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-21047799

RESUMO

Understanding the molecular mechanisms behind regulation of chromatin folding through covalent modifications of the histone N-terminal tails is hampered by a lack of accessible chromatin containing precisely modified histones. We study the internal folding and intermolecular self-association of a chromatin system consisting of saturated 12-mer nucleosome arrays containing various combinations of completely acetylated lysines at positions 5, 8, 12 and 16 of histone H4, induced by the cations Na(+), K(+), Mg(2+), Ca(2+), cobalt-hexammine(3+), spermidine(3+) and spermine(4+). Histones were prepared using a novel semi-synthetic approach with native chemical ligation. Acetylation of H4-K16, but not its glutamine mutation, drastically reduces cation-induced folding of the array. Neither acetylations nor mutations of all the sites K5, K8 and K12 can induce a similar degree of array unfolding. The ubiquitous K(+), (as well as Rb(+) and Cs(+)) showed an unfolding effect on unmodified arrays almost similar to that of H4-K16 acetylation. We propose that K(+) (and Rb(+)/Cs(+)) binding to a site on the H2B histone (R96-L99) disrupts H4K16 ε-amino group binding to this specific site, thereby deranging H4 tail-mediated nucleosome-nucleosome stacking and that a similar mechanism operates in the case of H4-K16 acetylation. Inter-array self-association follows electrostatic behavior and is largely insensitive to the position or nature of the H4 tail charge modification.


Assuntos
Histonas/química , Nucleossomos/química , Acetilação , Cátions/química , Cromatina/química , Simulação por Computador , Histonas/genética , Histonas/metabolismo , Lisina/metabolismo , Mutação , Conformação de Ácido Nucleico , Potássio/química , Conformação Proteica , Eletricidade Estática
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