Acetyl-Histone H4 (Lys91) Antibody

What is Histone H4 Lysine 91 acetylation and why is it significant in epigenetic research?

Histone H4 Lysine 91 acetylation (H4 Lysine 91 acetylation) represents a unique post-translational modification located in the globular core domain of histone H4, rather than in the more commonly studied N-terminal tail. This modification occurs at a critical interface between histone H3/H4 tetramers and H2A/H2B dimers, making it structurally significant for nucleosome integrity .

Unlike N-terminal histone modifications, Lysine 91 acetylation appears to play crucial roles in three fundamental nuclear processes:

• Chromatin assembly regulation

• DNA damage repair pathways

• Transcriptional silencing mechanisms

The strategic position of this modification at the histone dimer-tetramer interface suggests its role as a structural regulator of nucleosome stability . Research has demonstrated that mutations affecting this residue destabilize the histone octamer, leading to significant defects in chromatin structure .

How does Acetyl-Histone H4 (Lys91) differ from N-terminal tail histone acetylation marks?

The distinction between Histone H4 Lysine 91 acetylation and N-terminal modifications extends beyond simple positional differences, as outlined in the following comparison:

While N-terminal tail acetylation generally neutralizes positive charges to weaken histone-DNA interactions and promote open chromatin conformations, Histone H4 Lysine 91 acetylation appears to regulate the stability of the nucleosome core itself . This mechanistic distinction highlights the multifaceted roles of histone acetylation beyond the traditional view of tail modifications.

What are the recommended applications for Acetyl-Histone H4 (Lys91) antibodies?

Acetyl-Histone H4 (Lys91) antibodies can be effectively employed across multiple experimental techniques to detect and analyze this specific histone modification:

• Western Blotting (WB): Most commercial antibodies are validated for Western blot applications with recommended dilutions ranging from 1:1000-2000 . This approach allows for detection of Histone H4 Lysine 91 acetylation in cell or tissue lysates, typically producing a band at approximately 12-14 kDa.

• Chromatin Immunoprecipitation (ChIP): Anti-Acetyl-Histone H4 (Lys91) antibodies can be employed to map the genomic distribution of this modification. Previous studies have used ChIP to demonstrate enrichment of Histone H4 Lysine 91 acetylation in active regions of the genome with lower levels at telomeres and silenced loci .

• Immunohistochemistry (IHC): Some antibodies are specifically validated for immunohistochemical applications at dilutions of 1:200-500 , enabling visualization of Histone H4 Lysine 91 acetylation in fixed tissue sections.

• Dot Blot Assays: This technique can provide a rapid assessment of antibody specificity and modification presence in samples .

When selecting application-specific protocols, researchers should consider including appropriate controls to validate antibody specificity, particularly given the presence of multiple acetylation sites on histone H4.

How does Histone H4 Lysine 91 acetylation influence nucleosome stability and chromatin assembly?

Biochemical and genetic evidence indicates that Histone H4 Lysine 91 acetylation serves as a molecular regulator of nucleosome assembly through modulation of the histone octamer formation process. Located at the critical interface between histone components, this modification influences the strength of interactions that maintain nucleosome integrity .

Research utilizing hydroxyapatite chromatography has demonstrated that mutation of Histone H4 Lysine 91 destabilizes the interaction between H2A/H2B dimers and H3/H4 tetramers. When chromatin from wild-type and H4K91A mutant cells was applied to hydroxyapatite columns, histone H2B from mutant chromatin eluted at lower salt concentrations (0.7-0.8M NaCl) compared to wild-type (0.9M NaCl), indicating weakened interactions .

The model supported by experimental evidence suggests:

• Newly synthesized histone H4 is acetylated at Lysine 91 prior to deposition onto DNA

• This acetylation transiently modulates the association between tetramers and dimers

• Following assembly of H3/H4 tetramers onto DNA, deacetylation occurs

• Removal of the acetyl group strengthens interactions to complete stable octamer formation

This mechanism provides a dynamic regulatory step in chromatin assembly that is distinct from the role of N-terminal tail modifications .

What experimental evidence connects Histone H4 Lysine 91 acetylation to DNA damage repair pathways?

The relationship between Histone H4 Lysine 91 acetylation and DNA repair mechanisms has been established through multiple experimental approaches examining phenotypic consequences of disrupting this modification. Key evidence includes:

• Mutation Studies: Yeast strains containing an H4K91A mutation (mimicking constitutive acetylation) display pronounced sensitivity to DNA damaging agents, similar to strains with mutations in established chromatin assembly factors .

• Charge-Specific Effects: Comparative analysis of H4K91A, H4K91Q (mimicking acetylation), and H4K91R (maintaining positive charge) mutations revealed that only variants that eliminate the positive charge (A and Q) exhibit DNA damage sensitivity, while the arginine substitution that maintains positive charge rescues the phenotype .

• Chromatin Structure Analysis: MNase digestion patterns indicate that chromatin from H4K91A mutants is digested more rapidly than wild-type chromatin, suggesting altered chromatin accessibility that may impact DNA repair processes .

• Functional Conservation: The acetylation of Histone H4 Lysine 91 has been identified across evolutionarily diverse organisms from yeast to mammals, supporting its fundamental role in conserved cellular processes like DNA repair .

These findings collectively suggest that proper regulation of Histone H4 Lysine 91 acetylation is essential for maintaining genomic stability through efficient DNA damage repair pathways, likely by facilitating appropriate chromatin assembly during repair processes.

How does Histone H4 Lysine 91 acetylation interact with silent chromatin formation?

The relationship between Histone H4 Lysine 91 acetylation and silent chromatin regulation involves complex interactions with established silencing factors and other histone modifications. Experimental data reveals significant effects on multiple aspects of silent chromatin:

These findings suggest that Histone H4 Lysine 91 acetylation may influence silencing through mechanisms similar to H3 Lysine 79 methylation, where its presence in active chromatin helps confine silencing factors to appropriate genomic regions rather than directly participating in silencing complex assembly .

What validation strategies should be employed for Acetyl-Histone H4 (Lys91) antibodies?

Rigorous validation of Acetyl-Histone H4 (Lys91) antibodies is critical for ensuring experimental reliability. Researchers should implement a comprehensive validation strategy:

• Peptide Array Analysis: Test antibody reactivity against synthetic peptides containing:

  • Acetylated Histone H4 Lysine 91

  • Unmodified Histone H4 Lysine 91

  • Histone H4 peptides acetylated at other lysine residues (K5, K8, K12, K16)

  Research demonstrates that proper dot blot validation can confirm specificity for Histone H4 Lysine 91 acetylation without cross-reactivity to other acetylation sites .

• Western Blot Validation:

  • Compare recognition of histones from mammalian cells (containing Histone H4 Lysine 91 acetylation) versus recombinant histones expressed in E. coli (lacking this modification)

  • Include histone deacetylase inhibitor treatment (e.g., sodium butyrate) to increase acetylation levels as a positive control

  • Expected molecular weight for histone H4 is approximately 12-14 kDa

• Genetic Controls:

  • Utilize samples from H4K91A mutants as negative controls

  • Pre-incubate antibodies with lysates from H4K91A mutants to block potential cross-reactivity

• Cross-Species Reactivity Assessment:

  • Test antibody performance across species when working with non-human models

  • Commercial antibodies are typically validated for human, mouse, and rat samples

• Application-Specific Validation:

  • For ChIP applications, include input controls and known positive/negative genomic regions

  • For immunofluorescence, verify nuclear localization pattern and absence of signal in H4K91A mutants

Implementation of these validation steps establishes confidence in antibody specificity, crucial for accurate interpretation of experimental results.

What controls are essential for ChIP experiments targeting Histone H4 Lysine 91 acetylation?

Chromatin immunoprecipitation (ChIP) experiments with Acetyl-Histone H4 (Lys91) antibodies require carefully designed controls to ensure reliable data interpretation:

For quantitative ChIP analyses, researchers should apply appropriate normalization strategies and statistical methods to account for experimental variation across biological replicates.

How can researchers distinguish functional consequences of Histone H4 Lysine 91 acetylation from other histone modifications?

Dissecting the specific functional contributions of Histone H4 Lysine 91 acetylation requires experimental strategies that isolate this modification from other histone marks:

• Site-Specific Mutagenesis Approach:

  • Compare phenotypes of H4K91A (eliminates positive charge), H4K91Q (mimics acetylation), and H4K91R (maintains positive charge) mutations

  • These substitutions provide critical insights - for example, H4K91R rescues defects seen in H4K91A mutants, demonstrating the importance of charge state at this position

• Multi-Modification Analytical Techniques:

  • Perform sequential ChIP (Re-ChIP) to identify genomic regions where Histone H4 Lysine 91 acetylation co-occurs with other modifications

  • Apply mass spectrometry to analyze combinatorial modification patterns on single histone molecules

• Enzyme Manipulation Strategies:

  • Target histone acetyltransferases or deacetylases that specifically modify Histone H4 Lysine 91

  • While Hat1p is not the primary enzyme for this modification, identifying the responsible enzymes would provide tools for specific manipulation

• Genome-Wide Correlation Analysis:

  • Compare ChIP-seq profiles of Histone H4 Lysine 91 acetylation with other histone modifications

  • Identify distinct or overlapping genomic distributions and correlate with functional states

• Structural Biology Approaches:

  • Examine how Histone H4 Lysine 91 acetylation alters nucleosome crystal structure or cryo-EM density

  • Focus specifically on the interface between H3/H4 tetramers and H2A/H2B dimers where this residue resides

By implementing these complementary approaches, researchers can deconvolute the specific contributions of Histone H4 Lysine 91 acetylation to chromatin regulation from the broader landscape of histone modifications.

What is the latest understanding of Histone H4 Lysine 91 acetylation in chromatin compaction and accessibility?

Recent biophysical studies have expanded our understanding of how histone H4 acetylation influences chromatin structural dynamics, with implications for Lysine 91 acetylation. Research combining experimental and computational approaches has revealed:

The acetylation of histone H4 significantly alters the chemical environment of the basic patch residues (16-20) and leads to tail compaction that is partially mediated by transient intramolecular contacts between the basic patch and N-terminal amino acids . Though this study focused primarily on N-terminal acetylation sites, it demonstrates how acetylation can induce conformational changes that affect histone interactions.

For Histone H4 Lysine 91 specifically, its location at the critical interface between the H3/H4 tetramer and H2A/H2B dimers suggests that its acetylation could significantly impact nucleosome stability and chromatin higher-order structure. The destabilization of histone octamers observed with H4K91A mutations provides experimental support for this model .

Connecting these findings, we can postulate that Histone H4 Lysine 91 acetylation may contribute to chromatin accessibility in active genomic regions by:

• Transiently weakening dimer-tetramer interactions

• Facilitating nucleosome restructuring during transcription or replication

• Influencing higher-order chromatin folding dynamics

These mechanisms represent important areas for future investigation using advanced biophysical techniques.

How might researchers develop improved tools for studying Histone H4 Lysine 91 acetylation?

The advancement of research on Histone H4 Lysine 91 acetylation would benefit from several technological innovations and methodological improvements:

• Next-Generation Antibodies:

  • Development of recombinant antibodies with enhanced specificity

  • Creation of bi-specific antibodies that recognize Histone H4 Lysine 91 acetylation in combination with other modifications

  • Advanced validation using proteomics approaches to confirm target specificity

• Engineered Cellular Systems:

  • CRISPR-based platforms to introduce H4K91 mutations in diverse cell types

  • Development of systems for rapid induction or removal of Histone H4 Lysine 91 acetylation

  • Reporter constructs linked to Histone H4 Lysine 91 acetylation states

• Advanced Imaging Approaches:

  • Super-resolution microscopy techniques to visualize Histone H4 Lysine 91 acetylation distribution in nuclear territories

  • Live-cell imaging systems to track dynamic changes in this modification

  • Proximity ligation assays to detect interactions between modified nucleosomes and regulatory proteins

• Single-Cell Technologies:

  • Methods for detecting Histone H4 Lysine 91 acetylation in single-cell epigenomic assays

  • Integration with single-cell transcriptomics to correlate modification patterns with gene expression

• Computational Models:

  • Molecular dynamics simulations of how Histone H4 Lysine 91 acetylation affects nucleosome stability

  • Predictive algorithms for identifying genomic regions enriched in this modification

  • Integration of multiple data types to build comprehensive models of modification function

These technical advances would enhance our ability to investigate the dynamics and functional significance of Histone H4 Lysine 91 acetylation across diverse biological contexts.

What are the unresolved questions regarding Histone H4 Lysine 91 acetylation in disease contexts?

Several critical questions remain unexplored regarding the potential role of Histone H4 Lysine 91 acetylation in disease pathogenesis:

• Cancer Biology:

  • Is Histone H4 Lysine 91 acetylation dysregulated in specific cancer types?

  • Could altered patterns of this modification contribute to genomic instability?

  • Might targeting enzymes that regulate Histone H4 Lysine 91 acetylation provide therapeutic opportunities?

• Neurodegenerative Disorders:

  • Does Histone H4 Lysine 91 acetylation play a role in neural chromatin regulation?

  • Are there connections between Histone H4 Lysine 91 acetylation and age-related changes in chromatin structure?

  • Could this modification influence neuronal DNA damage repair efficiency?

• Developmental Disorders:

  • How is Histone H4 Lysine 91 acetylation regulated during embryonic development?

  • Are there critical windows where proper regulation of this modification is essential?

  • Could congenital disorders involve disruption of pathways affecting this modification?

• Inflammation and Immunity:

  • Does Histone H4 Lysine 91 acetylation change during immune cell activation?

  • Could this modification participate in establishing immunological memory?

  • Is there interplay between environmental factors and Histone H4 Lysine 91 acetylation patterns?

• Metabolic Regulation:

  • How might cellular metabolic state influence Histone H4 Lysine 91 acetylation levels?

  • Could this modification respond to nutritional signals to adjust chromatin states?

  • Is there crosstalk between Histone H4 Lysine 91 acetylation and metabolic disorders?

Addressing these questions will require interdisciplinary approaches combining clinical samples, disease models, and advanced epigenomic methodologies to elucidate potential connections between Histone H4 Lysine 91 acetylation and human disease.