Zhongyi Cheng

Identification of 67 Histone Marks and Histone Lysine Crotonylation as a New Type of Histone Modification

We report the identification of 67 previously undescribed histone modifications, increasing the current number of known histone marks by about 70%. We further investigated one of the marks, lysine crotonylation (Kcr), confirming that it represents an evolutionarily-conserved histone posttranslational modification. The unique structure and genomic localization of histone Kcr suggest that it is mechanistically and functionally different from histone lysine acetylation (Kac). Specifically, in both human somatic and mouse male germ cell genomes, histone Kcr marks either active promoters or potential enhancers. In male germinal cells immediately following meiosis, Kcr is enriched on sex chromosomes and specifically marks testis-specific genes, including a significant proportion of X-linked genes that escape sex chromosome inactivation in haploid cells. These results therefore dramatically extend the repertoire of histone PTM sites and designate Kcr as a specific mark of active sex chromosome-linked genes in postmeiotic male germ cells.

The first identification of lysine malonylation substrates and its regulatory enzyme

Protein post-translational modifications (PTMs) at the lysine residue, such as lysine methylation, acetylation, and ubiquitination, are diverse, abundant, and dynamic. They play a key role in the regulation of diverse cellular physiology. Here we report discovery of a new type of lysine PTM, lysine malonylation (Kmal). Kmal was initially detected by mass spectrometry and protein sequence-database searching. The modification was comprehensively validated by Western blot, tandem MS, and high-performance liquid chromatography of synthetic peptides, isotopic labeling, and identification of multiple Kmal substrate proteins. Kmal is a dynamic and evolutionarily conserved PTM observed in mammalian cells and bacterial cells. In addition, we demonstrate that Sirt5, a member of the class III lysine deacetylases, can catalyze lysine demalonylation and lysine desuccinylation reactions both in vitro and in vivo. This result suggests the possibility of nondeacetylation activity of other class III lysine deacetylases, especially those without obvious acetylation protein substrates. Our results therefore reveal a new type of PTM pathway and identify the first enzyme that can regulate lysine malonylation and lysine succinylation status.

Lysine Succinylation and Lysine Malonylation in Histones

Histone protein post-translational modifications (PTMs) are significant for gene expression and DNA repair. Here we report the identification and validation of a new type of PTM in histones, lysine succinylation. The identified lysine succinylated histone peptides were verified by MS/MS of synthetic peptides, HPLC co-elution, and isotopic labeling. We identified 13, 7, 10, and 7 histone lysine succinylation sites in HeLa, mouse embryonic fibroblast, Drosophila S2, and Saccharomyces cerevisiae cells, respectively. We demonstrated that this histone PTM is present in all eukaryotic cells we examined. Mutagenesis of succinylation sites followed by functional assays implied that histone lysine succinylation can cause unique functional consequences. We also identified one and two histone lysine malonylation sites in HeLa and S. cerevisiae cells, respectively. Our results therefore increase potential combinatorial diversity of histone PTMs and suggest possible new connections between histone biology and metabolism.

Comprehensive Profiling of Protein Lysine Acetylation in Escherichia coli

Protein lysine acetylation plays a key role in regulating chromatin dynamics, gene expression and metabolic pathways in eukaryotes, and, thus, contributes to diverse cellular processes like transcription, cell cycle regulation, and apoptosis. Although recent evidence suggests that acetylated proteins impact broadly cellular functions in prokaryotes, the substrates and localization of this modification remain widely unknown due to the limitations of analytical methods. Comprehensive identification of protein acetylation is a major bottleneck due to its dynamic property and pretty low abundance. A complete atlas of acetylome will significantly advance our understanding of this modification functions in prokaryotes. To achieve this goal, we have developed an intergraded approach to identifying lysine acetylation. Combining immunoaffinity enrichment with high sensitive mass spectrometry, we identified 349 acetylated proteins and addressed 1070 acetylation sites in Escherichia coli. To our knowledge, the acetylated proteins and acetylated sites were increased to 3 times and 8 times, respectively, compared to that in previous report. To further characterize this modification, we classified acetylated proteins into several groups according to cell components, molecular functions and biological process. Additionally, interaction networks and high confident domains architectures of acetylated proteins were investigated with the aid of bioinformatics tools. Finally, the acetylated metabolic enzymes were analyzed on the basis of acetylated proteins identified by proteomic survey in E. coli. Our study has demonstrated that the combined approach is powerful for identification and characterization of protein lysine acetylation on a large scale. These results not only greatly expand the number of acetylated proteins, but also provide a series of important information including localization, networks and characterization of acetylome.

Quantitative Acetylome Analysis Reveals the Roles of SIRT1 in Regulating Diverse Substrates and Cellular Pathways

Despite of the progress in identifying many Lys acetylation (Kac) proteins, Kac substrates for Kac-regulatory enzymes remain largely unknown, presenting a major knowledge gap in Kac biology. Here we identified and quantified 4623 Kac sites in 1800 Kac proteins in SIRT1+/+ and SIRT1−/− MEF cells, representing the first study to reveal an enzyme-regulated Kac subproteome and the largest Lys acetylome reported to date from a single study. Four hundred eighty-five Kac sites were enhanced by more than 100% after SIRT1 knockout. Our results indicate that SIRT1 regulates the Kac states of diverse cellular pathways. Interestingly, we found that a number of acetyltransferases and major acetyltransferase complexes are targeted by SIRT1. Moreover, we showed that the activities of the acetyltransferases are regulated by SIRT1-mediated deacetylation. Taken together, our results reveal the Lys acetylome in response to SIRT1, provide new insights into mechanisms of SIRT1 function, and offer biomarker candidates for the clinical evaluation of SIRT1-activator compounds.

Molecular Characterization of Propionyllysines in Non-histone Proteins

Lysine propionylation and butyrylation are protein modifications that were recently identified in histones. The molecular components involved in the two protein modification pathways are unknown, hindering further functional studies. Here we report identification of the first three in vivo non-histone protein substrates of lysine propionylation in eukaryotic cells: p53, p300, and CREB-binding protein. We used mass spectrometry to map lysine propionylation sites within these three proteins. We also identified the first two in vivo eukaryotic lysine propionyltransferases, p300 and CREB-binding protein, and the first eukaryotic depropionylase, Sirt1. p300 was able to perform autopropionylation on lysine residues in cells. Our results suggest that lysine propionylation, like lysine acetylation, is a dynamic and regulatory post-translational modification. Based on these observations, it appears that some enzymes are common to the lysine propionylation and lysine acetylation regulatory pathways. Our studies therefore identified first several important players in lysine propionylation pathway.

Dynamic Competing Histone H4 K5K8 Acetylation and Butyrylation Are Hallmarks of Highly Active Gene Promoters

Summary Recently discovered histone lysine acylation marks increase the functional diversity of nucleosomes well beyond acetylation. Here, we focus on histone butyrylation in the context of sperm cell differentiation. Specifically, we investigate the butyrylation of histone H4 lysine 5 and 8 at gene promoters where acetylation guides the binding of Brdt, a bromodomain-containing protein, thereby mediating stage-specific gene expression programs and post-meiotic chromatin reorganization. Genome-wide mapping data show that highly active Brdt-bound gene promoters systematically harbor competing histone acetylation and butyrylation marks at H4 K5 and H4 K8. Despite acting as a direct stimulator of transcription, histone butyrylation competes with acetylation, especially at H4 K5, to prevent Brdt binding. Additionally, H4 K5K8 butyrylation also marks retarded histone removal during late spermatogenesis. Hence, alternating H4 acetylation and butyrylation, while sustaining direct gene activation and dynamic bromodomain binding, could impact the final male epigenome features.

Proteomic and Biochemical Studies of Lysine Malonylation Suggest Its Malonic Aciduria-associated Regulatory Role in Mitochondrial Function and Fatty Acid Oxidation

The protein substrates of sirtuin 5-regulated lysine malonylation (Kmal) remain unknown, hindering its functional analysis. In this study, we carried out proteomic screening, which identified 4042 Kmal sites on 1426 proteins in mouse liver and 4943 Kmal sites on 1822 proteins in human fibroblasts. Increased malonyl-CoA levels in malonyl-CoA decarboxylase (MCD)-deficient cells induces Kmal levels in substrate proteins. We identified 461 Kmal sites showing more than a 2-fold increase in response to MCD deficiency as well as 1452 Kmal sites detected only in MCD−/− fibroblast but not MCD+/+ cells, suggesting a pathogenic role of Kmal in MCD deficiency. Cells with increased lysine malonylation displayed impaired mitochondrial function and fatty acid oxidation, suggesting that lysine malonylation plays a role in pathophysiology of malonic aciduria. Our study establishes an association between Kmal and a genetic disease and offers a rich resource for elucidating the contribution of the Kmal pathway and malonyl-CoA to cellular physiology and human diseases.

Bioinformatic Analysis and Post-Translational Modification Crosstalk Prediction of Lysine Acetylation

Recent proteomics studies suggest high abundance and a much wider role for lysine acetylation (K-Ac) in cellular functions. Nevertheless, cross influence between K-Ac and other post-translational modifications (PTMs) has not been carefully examined. Here, we used a variety of bioinformatics tools to analyze several available K-Ac datasets. Using gene ontology databases, we demonstrate that K-Ac sites are found in all cellular compartments. KEGG analysis indicates that the K-Ac sites are found on proteins responsible for a diverse and wide array of vital cellular functions. Domain structure prediction shows that K-Ac sites are found throughout a wide variety of protein domains, including those in heat shock proteins and those involved in cell cycle functions and DNA repair. Secondary structure prediction proves that K-Ac sites are preferentially found in ordered structures such as alpha helices and beta sheets. Finally, by mutating K-Ac sites in silico and predicting the effect on nearby phosphorylation sites, we demonstrate that the majority of lysine acetylation sites have the potential to impact protein phosphorylation, methylation, and ubiquitination status. Our work validates earlier smaller-scale studies on the acetylome and demonstrates the importance of PTM crosstalk for regulation of cellular function.

A Chemical Proteomics Approach for Global Analysis of Lysine Monomethylome Profiling

Methylation of lysine residues on histone proteins is known to play an important role in chromatin structure and function. However, non-histone protein substrates of this modification remain largely unknown. An effective approach for system-wide analysis of protein lysine methylation, particularly lysine monomethylation, is lacking. Here we describe a chemical proteomics approach for global screening for monomethyllysine substrates, involving chemical propionylation of monomethylated lysine, affinity enrichment of the modified monomethylated peptides, and HPLC/MS/MS analysis. Using this approach, we identified with high confidence 446 lysine monomethylation sites in 398 proteins, including three previously unknown histone monomethylation marks, representing the largest data set of protein lysine monomethylation described to date. Our data not only confirms previously discovered lysine methylation substrates in the nucleus and spliceosome, but also reveals new substrates associated with diverse biological processes. This method hence offers a powerful approach for dynamic study of protein lysine monomethylation under diverse cellular conditions and in human diseases.