Unexpected extensive lysine acetylation in the trump-card antibiotic producer Streptomyces roseosporus revealed by proteome-wide profiling

Protein Acetylation and Its Role in Bacterial Virulence

Protein acetylation is a universal post-translational modification which is found in both eukaryotes and prokaryotes. This process is achieved enzymatically by the protein acetyltransferase Pat, and nonenzymatically by metabolic intermediates (e.g., acetyl phosphate) in bacteria. Protein acetylation plays a role in bacterial chemotaxis, metabolism, DNA replication, and other cellular processes. Recently, accumulating evidence has suggested that protein acetylation might be involved in bacterial virulence because a number of bacterial virulence factors are acetylated. In this review, we summarize the progress in understanding bacterial protein acetylation and discuss how it mediates bacterial virulence.

Global analysis of protein lysine succinylation profiles in common wheat

Background

Protein lysine succinylation is an important post-translational modification and plays a critical regulatory role in almost every aspects of cell metabolism in both eukaryotes and prokaryotes. Common wheat is one of the major global cereal crops. However, to date, little is known about the functions of lysine succinylation in this plant. Here, we performed a global analysis of lysine succinylation in wheat and examined its overlap with lysine acetylation.

Results

In total, 330 lysine succinylated modification sites were identified in 173 proteins. Bioinformatics analysis showed that the modified proteins are distributed in multiple subcellular compartments and are involved in a wide variety of biological processes such as photosynthesis and the Calvin-Benson cycle, suggesting an important role for lysine succinylation in these processes. Five putative succinylation motifs were identified. A protein interaction network analysis revealed that diverse interactions are modulated by protein succinylation. Moreover, 21 succinyl-lysine sites were found to be acetylated at the same position, and 33 proteins were modified by both acetylation and succinylation, suggesting an extensive overlap between succinylation and acetylation in common wheat. Comparative analysis indicated that lysine succinylation is conserved between common wheat and Brachypodium distachyon.

Conclusions

These results suggest that lysine succinylation is involved in diverse biological processes, especially in photosynthesis and carbon fixation. This systematic analysis represents the first global analysis of lysine succinylation in common wheat and provides an important resource for exploring the physiological role of lysine succinylation in this cereal crop and likely in all plants.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3698-2) contains supplementary material, which is available to authorized users.

Global Insight into Lysine Acetylation Events and Their Links to Biological Aspects in Beauveria bassiana, a Fungal Insect Pathogen

Lysine acetylation (Kac) events in filamentous fungi are poorly explored. Here we show a lysine acetylome generated by LC-MS/MS analysis of immunoaffinity-based Kac peptides from normal hyphal cells of Beauveria bassiana, a fungal entomopathogen. The acetylome comprised 283 Kac proteins and 464 Kac sites. These proteins were enriched to eight molecular functions, 20 cellular components, 27 biological processes, 20 KEGG pathways and 12 subcellular localizations. All Kac sites were characterized as six Kac motifs, including a novel motif (KacW) for 26 Kac sites of 17 unknown proteins. Many Kac sites were predicted to be multifunctional, largely expanding the fungal Kac events. Biological importance of identified Kac sites was confirmed through functional analysis of Kac sites on Pmt1 and Pmt4, two O-mannosyltransferases. Singular site mutations (K88R and K482R) of Pmt1 resulted in impaired conidiation, attenuated virulence and decreased tolerance to oxidation and cell wall perturbation. These defects were close to or more severe than those caused by the deletion of pmt1. The Pmt4 K360R mutation facilitated colony growth under normal and stressful conditions and enhanced the fungal virulence. Our findings provide the first insight into the Kac events of B. bassiana and their links to the fungal potential against insect pests.

Protein acetylation involved in streptomycin biosynthesis in Streptomyces griseus

Protein acetylation, the reversible addition of an acetyl group to lysine residues, is a protein post-translational modification ubiquitous in living cells. Although the involvement of protein acetylation in the regulation of primary metabolism has been revealed, the function of protein acetylation is largely unknown in secondary metabolism. Here, we characterized protein acetylation in Streptomyces griseus, a streptomycin producer. Protein acetylation was induced in the stationary and sporulation phases in liquid and solid cultures, respectively, in S. griseus. By comprehensive acetylome analysis, we identified 134 acetylated proteins with 162 specific acetylated sites. Acetylation was found in proteins related to primary metabolism and translation, as in other bacteria. However, StrM, a deoxysugar epimerase involved in streptomycin biosynthesis, was identified as a highly acetylated protein by 2-DE-based proteomic analysis. The Lys70 residue, which is critical for the enzymatic activity of StrM, was the major acetylation site. Thus, acetylation of Lys70 was presumed to abolish enzymatic activity of StrM. In accordance with this notion, an S. griseus mutant producing the acetylation-mimic K70Q StrM hardly produced streptomycin, though the K70Q mutation apparently decreased the stability of StrM. A putative lysine acetyltransferase (KAT) SGR1683 in S. griseus, as well as the Escherichia coli KAT YfiQ, acetylated Lys70 of StrM in vitro. Furthermore, absolute quantification analysis estimated that 13% of StrM molecules were acetylated in mycelium grown in solid culture for 3days. These results indicate that StrM acetylation is of biological significance. We propose that StrM acetylation functions as a limiter of streptomycin biosynthesis in S. griseus.

BIOLOGICAL SIGNIFICANCE

Protein acetylation has been extensively studied not only in eukaryotes, but also in prokaryotes. The acetylome has been analyzed in more than 14 bacterial species. Here, by comprehensive acetylome analysis, we showed that acetylation was found in proteins related to primary metabolism and translation in Streptomyces griseus, similarly to other bacteria. However, five proteins involved in secondary metabolism were also identified as acetylated proteins; these proteins are enzymes in the biosynthesis of streptomycin (StrB1 and StrS), grixazone (GriF), a nonribosomal peptide (NRPS1-2), and a siderophore (AlcC). Additionally, StrM in streptomycin biosynthesis was identified as a highly acetylated protein by 2-DE-based proteomic analysis; approximately 13% of StrM molecules were acetylated. The acetylation occurs at Lys70 to abolish the enzymatic activity of StrM, suggesting that StrM acetylation functions as a limiter of streptomycin biosynthesis in S. griseus. This is the first detailed analysis of protein acetylation of an enzyme involved in secondary metabolism.

Systematic analysis of the lysine acetylome in Fusarium graminearum

BACKGROUND

Lysine acetylation in proteins is a ubiquitous and conserved post-translational modification, playing a critical regulatory role in almost every aspect of living cells. Although known for many years, its function remains elusive in Fusarium graminearum, one of the most important necrotrophic plant pathogens with huge economic impact.

RESULTS

By the combination of affinity enrichment and high-resolution LC-MS/MS analysis, large-scale lysine acetylome analysis was performed. In total, 577 lysine acetylation sites matched to 364 different proteins were identified. Bioinformatics analysis of the acetylome showed that the acetylated proteins are involved in a wide range of cellular functions and exhibit diverse subcellular localizations. Remarkably, 10 proteins involved in the virulence or DON (deoxynivalenol) biosynthesis were found to be acetylated, including 4 transcription factors, 4 protein kinases and 2 phosphatases. Protein-protein interaction network analysis revealed that acetylated protein complexes are involved in diversified interactions.

CONCLUSIONS

This work provides the first comprehensive survey of a possible lysine acetylome in F. graminearum and reveals previously unappreciated roles of lysine acetylation in the regulation of diverse biological processes. This work provides a resource for functional analysis of acetylated proteins in filamentous fungi.

Malonylome analysis of rhizobacterium Bacillus amyloliquefaciens FZB42 reveals involvement of lysine malonylation in polyketide synthesis and plant-bacteria interactions

Using the combination of affinity enrichment and high-resolution LC-MS/MS analysis, we performed a large-scale lysine malonylation analysis in the model representative of Gram-positive plant growth-promoting rhizobacteria (PGPR), Bacillus amyloliquefaciens FZB42. Altogether, 809 malonyllysine sites in 382 proteins were identified. The bioinformatic analysis revealed that lysine malonylation occurs on the proteins involved in a variety of biological functions including central carbon metabolism, fatty acid biosynthesis and metabolism, NAD(P) binding and translation machinery. A group of proteins known to be implicated in rhizobacterium-plant interaction were also malonylated; especially, the enzymes responsible for antibiotic production including polyketide synthases (PKSs) and nonribosomal peptide synthases (NRPSs) were highly malonylated. Furthermore, our analysis showed malonylation occurred on proteins structure with higher surface accessibility and appeared to be conserved in many bacteria but not in archaea. The results provide us valuable insights into the potential roles of lysine malonylation in governing bacterial metabolism and cellular processes.

BIOLOGICAL SIGNIFICANCE

Although in mammalian cells some important findings have been discovered that protein malonylation is related to basic metabolism and chronic disease, few studies have been performed on prokaryotic malonylome. In this study, we determined the malonylation profiles of Bacillus amyloliquefaciens FZB42, a model organism of Gram-positive plant growth-promoting rhizobacteria. FZB42 is known for the extensive investigations on its strong ability of producing antimicrobial polyketides and its potent activities of stimulating plant growth. Our analysis shows that malonylation is highly related to the polyketide synthases and the proteins involved bacterial interactions with plants. The results not only provide one of the first malonylomes for exploring the biochemical nature of bacterial proteins, but also shed light on the better understanding of bacterial antibiotic biosynthesis and plant-microbe interaction.

Proteome-wide analysis of lysine acetylation in adult Schistosoma japonicum worm

Lysine acetylation, a ubiquitous and conserved posttranslational modification, has recently been shown to participate in many diverse non-chromatin-associated biological processes in prokaryotes and eukaryotes. However, the full extent and functional significance of acetylation in Schistosoma japonicum is still unknown. To investigate the nature, extent, and biological functions of lysine acetylation in schistosomes, immunoaffinity-based acetyl-lysine peptide enrichment, integrated with mass spectrometry, was used to comprehensively characterize the lysine-acetylated proteins in this parasite. In total, 1109 acetylated proteins and 2393 acetylation sites in S. japonicum were identified, representing the largest acetylome yet reported in a parasite. In a bioinformatic analysis showed that these acetylated proteins were mainly enriched in the biological process categories of metabolism, gene expression, translation, and transport. The classification according to molecular function revealed that the largest class involved the catalytic activity of different enzymes, including oxidoreductase, transferase, and pyrophosphatase activities. Most of the acetylated proteins in the cellular component category occurred in the cytoplasm, membrane, cytoskeleton, and nucleus. These data demonstrate the generality of lysine acetylation and provide the first global survey of acetylation in schistosomes. Our findings are an exciting starting point for the further exploration of the functions of acetylation in the biology of this parasite.

SIGNIFICANCE

Schistosomiasis is one of the world's most prevalent and neglected tropical parasitic zoonotic diseases, and it causes almost 200,000 deaths annually. To control and eradicate schistosomiasis, effective vaccines are urgently required, and drug targets that are essential for schistosome survival must be identified in fundamental studies of schistosome biology. Posttranslational modifications are complex, fundamental, and important mechanisms that regulate the physiological functions of organisms. Lysine acetylation, a ubiquitous and conserved posttranslational modification, has recently been shown to participate in many diverse non-chromatin-associated biological processes in prokaryotes and eukaryotes. However, the full extent and functional significance of acetylation in Schistosoma japonicum is still unknown. To investigate the nature, extent, and biological functions of lysine acetylation in S. japonicum, we employ immunoaffinity-based acetyl-lysine peptide enrichment, integrated with mass spectrometry to comprehensively characterize the lysine-acetylated proteins in this parasite. The results of our data demonstrate the generality of lysine acetylation and provide the first global survey of acetylation in schistosomes. Our findings are an exciting starting point for the further exploration of the functions of acetylation in the biology of this parasite. Meanwhile, identifying the mechanisms and proteins targeted by acetylation may also provide a promising avenue for specific drug design and the development of sophisticated therapeutic strategies.

Systematic analysis of the lysine acetylome of the pathogenic bacterium Spiroplasma eriocheiris reveals acetylated proteins related to metabolism and helical structure

Post-translational modifications such as acetylation are an essential regulatory mechanism of protein function. Spiroplasma eriocheiris, with no cell wall and a helical structure, is a novel pathogen of freshwater crustacean. There is no other evidence of acylation (such as succinylation and propionylation) except acetylation genes in S. eriocheiris concise genome. So the acetylation may play an important role in S. eriocheiris. Here, we conducted the first lysine acetylome in S. eriocheiris. We identified 2567 lysine acetylation sites in 555 proteins, which account for 44.69% of the total proteins in this bacterium. To date, this is the highest ratio of acetylated proteins that have been identified in bacteria. Fifteen types of acetylated peptide sequence motifs were revealed from the acetylome. Forty-five lysine-acetylated proteins showed homology with acetylated proteins previously identified from Escherichia coli, Vibrio parahemolyticus and Mycobacterium tuberculosis. Notably, most proteins in glycolysis and all proteins in the arginine deiminase system were acetylated. Meanwhile, the cell skeleton proteins (Fibril and Mrebs) were all acetylated the observed acetylation also played an important role in cell skeleton formation. The results imply previously unreported hidden layers of post-translational regulation in lysine acetylation that define the functional state of Spiroplasma.

BIOLOGICAL SIGNIFICANCE

This is the first time to analyze PTM of Spiroplasma. This is the highest ratio of acetylated proteins that have been identified in bacteria. S. eriocheiris lysine acetylome reveals acetylated proteins related to metabolism and helical structure. These data provide an important resource to elucidate the role of acetylation in Spiroplasma cellular physiology.

Acetylome analysis reveals the involvement of lysine acetylation in diverse biological processes in Phytophthora sojae

Lysine acetylation is a dynamic and highly conserved post-translational modification that plays an important regulatory role in almost every aspects of cell metabolism in both eukaryotes and prokaryotes. Phytophthora sojae is one of the most important plant pathogens due to its huge economic impact. However, to date, little is known about the functions of lysine acetylation in this Phytopthora. Here, we conducted a lysine acetylome in P. sojae. Overall, 2197 lysine acetylation sites in 1150 proteins were identified. The modified proteins are involved in diverse biological processes and are localized to multiple cellular compartments. Importantly, 7 proteins involved in the pathogenicity or the secretion pathway of P. sojae were found to be acetylated. These data provide the first comprehensive view of the acetylome of P. sojae and serve as an important resource for functional analysis of lysine acetylation in plant pathogens.

Systematic Analysis of the Lysine Acetylome in Candida albicans

Candida albicans (C. albicans) is a worldwide cause of fungal infectious diseases. As a general post-translational modification (PTM), lysine acetylation of proteins play an important regulatory role in almost every cell. In our research, we used a high-resolution proteomic technique (LC-MS/MS) to present the comprehensive analysis of the acetylome in C. albicans. In general, we detected 477 acetylated proteins among all 9038 proteins (5.28%) in C. albicans, which had 1073 specific acetylated sites. The bioinformatics analysis of the acetylome showed a significant role in the regulation of metabolism. To be more precise, proteins involved in carbon metabolism and biosynthesis were the underlying objectives of acetylation. Besides, through the study of the acetylome, we found a universal rule in acetylated motifs: the +4, +5, or +6 position, which is an alkaline residue with a long side chain (K or R), and the +1 or +2 position, which is a residue with a long side chain (Y, H, W, or F). To the best of our knowledge, all screening acetylated histone sites of this study have not been previously reported. Moreover, protein-protein interaction network (PPI) study demonstrated that a variety of connections in glycolysis/gluconeogenesis, oxidative phosphorylation, and the ribosome were modulated by acetylation and phosphorylation, but the phosphorylated proteins in oxidative phosphorylation PPI network were not abundant, which indicated that acetylation may have a more significant effect than phosphorylation on oxidative phosphorylation. This is the first study of the acetylome in human pathogenic fungi, providing an important starting point for the in-depth discovery of the functional analysis of acetylated proteins in such fungal pathogens.

Temporal Regulation of the Bacillus subtilis Acetylome and Evidence for a Role of MreB Acetylation in Cell Wall Growth

The past decade highlighted N^ε-lysine acetylation as a prevalent posttranslational modification in bacteria. However, knowledge regarding the physiological importance and temporal regulation of acetylation has remained limited. To uncover potential regulatory roles for acetylation, we analyzed how acetylation patterns and abundances change between growth phases in B. subtilis. To demonstrate that the identification of cell growth-dependent modifications can point to critical regulatory acetylation events, we further characterized MreB, the cell shape-determining protein. Our findings led us to propose a role for MreB acetylation in controlling cell width by restricting cell wall growth.

N^ε-Lysine acetylation has been recognized as a ubiquitous regulatory posttranslational modification that influences a variety of important biological processes in eukaryotic cells. Recently, it has been realized that acetylation is also prevalent in bacteria. Bacteria contain hundreds of acetylated proteins, with functions affecting diverse cellular pathways. Still, little is known about the regulation or biological relevance of nearly all of these modifications. Here we characterize the cellular growth-associated regulation of the Bacillus subtilis acetylome. Using acetylation enrichment and quantitative mass spectrometry, we investigate the logarithmic and stationary growth phases, identifying over 2,300 unique acetylation sites on proteins that function in essential cellular pathways. We determine an acetylation motif, EK(ac)(D/Y/E), which resembles the eukaryotic mitochondrial acetylation signature, and a distinct stationary-phase-enriched motif. By comparing the changes in acetylation with protein abundances, we discover a subset of critical acetylation events that are temporally regulated during cell growth. We functionally characterize the stationary-phase-enriched acetylation on the essential shape-determining protein MreB. Using bioinformatics, mutational analysis, and fluorescence microscopy, we define a potential role for the temporal acetylation of MreB in restricting cell wall growth and cell diameter.

IMPORTANCE The past decade highlighted N^ε-lysine acetylation as a prevalent posttranslational modification in bacteria. However, knowledge regarding the physiological importance and temporal regulation of acetylation has remained limited. To uncover potential regulatory roles for acetylation, we analyzed how acetylation patterns and abundances change between growth phases in B. subtilis. To demonstrate that the identification of cell growth-dependent modifications can point to critical regulatory acetylation events, we further characterized MreB, the cell shape-determining protein. Our findings led us to propose a role for MreB acetylation in controlling cell width by restricting cell wall growth.

Proteomic characterization of Nα- and Nε-acetylation in Acinetobacter baumannii

Nα- and Nε-acetylation represent a pivotal post-translational modification used by both eukaryotes and prokaryotes to modulate diverse biological processes. Acinetobacter baumannii has been described as an important nosocomial pathogen for the past 30 years, frequently involved in ventilator-associated pneumonia, bloodstream and urinary tract infections. Many aspects of the biology of A. baumannii remain elusive, in particular the extent and function of N-acetylation. We investigated here N-acetylation in A. baumannii strain ATCC 17978 by proteomic analysis, and we showed the usefulness of using different analytical approaches. Overall, we identified 525 N-acetylated proteins in which, 145 were Nα-acetylated and 411 were Nε-acetylated. Among them, 41 proteins carried both types of N-acetylation. We found that N-acetylation may play a role in biofilm formation, bacterial virulence (e.g. in several iron acquisition pathways), as well as a number of phenotypes, such as, stress adaptation and drug resistance.

BIOLOGICAL SIGNIFICANCE

This study is the first to perform the N-acetylome of A. baumannii using different analytical approaches. Each analytical tool permitted to characterize distinctive modified peptides. The combination of all these methods allowed us to identify 145 and 411 Nα- and Nε-acetylated proteins. Besides the fact that acetylation was involved in central metabolism as previously described in other bacteria, some N-acetylated proteins showed interesting role in bacterial virulence (iron acquisition), biofilm formation, stress adaptation and drug resistance of A. baumannii.

Bacterial Electron Transfer Chains Primed by Proteomics

Electron transport phosphorylation is the central mechanism for most prokaryotic species to harvest energy released in the respiration of their substrates as ATP. Microorganisms have evolved incredible variations on this principle, most of these we perhaps do not know, considering that only a fraction of the microbial richness is known. Besides these variations, microbial species may show substantial versatility in using respiratory systems. In connection herewith, regulatory mechanisms control the expression of these respiratory enzyme systems and their assembly at the translational and posttranslational levels, to optimally accommodate changes in the supply of their energy substrates. Here, we present an overview of methods and techniques from the field of proteomics to explore bacterial electron transfer chains and their regulation at levels ranging from the whole organism down to the Ångstrom scales of protein structures. From the survey of the literature on this subject, it is concluded that proteomics, indeed, has substantially contributed to our comprehending of bacterial respiratory mechanisms, often in elegant combinations with genetic and biochemical approaches. However, we also note that advanced proteomics offers a wealth of opportunities, which have not been exploited at all, or at best underexploited in hypothesis-driving and hypothesis-driven research on bacterial bioenergetics. Examples obtained from the related area of mitochondrial oxidative phosphorylation research, where the application of advanced proteomics is more common, may illustrate these opportunities.

Post-translational modifications in Pseudomonas aeruginosa revolutionized by proteomic analysis

Pseudomonas aeruginosa is an opportunistic pathogen that causes severe infections in vulnerable individuals. It is known that post-translational modifications (PTMs) play a key role in bacterial physiology. Their characterization is still challenging and the recent advances in proteomics allow large-scale and high-throughput analyses of PTMs. Here, we provide an overview of proteomic data about the modified proteins in P. aeruginosa. We emphasize the significant contribution of proteomics in knowledge enhancement of PTMs (phosphorylation, N-acetylation and glycosylation) and we discuss their importance in P. aeruginosa physiology.

Data for global lysine-acetylation analysis in rice (Oryza sativa)

Rice is one of the most important crops for human consumption and is a staple food for over half of the world׳s population (Yu et al., 2002) [1]. A systematic identification of the lysine acetylome was performed by our research (Xiong et al., 2016) [2]. Rice plant samples were collected from 5 weeks old seedlings (Oryza sativa, Nipponbare). After the trypsin digestion and immunoaffinity precipitation, LC–MS/MS approach was used to identify acetylated peptides. After the collected MS/MS data procession and GO annotation, the InterProScan was used to annotate protein domain. Subcellular localization of the identified acetylated proteins was predicted by WoLF PSORT. The KEGG pathway database was used to annotate identified acetylated protein interactions, reactions, and relations. The data, supplied in this article, are related to “A comprehensive catalog of the lysine-acetylation targets in rice (O. sativa) based on proteomic analyses” by Xiong et al. (2016) [2].

Mass Spectrometry-Based Bacterial Proteomics: Focus on Dermatologic Microbial Pathogens

The composition of human skin acts as a natural habitat for various bacterial species that function in a commensal and symbiotic fashion. In a healthy individual, bacterial flora serves to protect the host. Under certain conditions such as minor trauma, impaired host immunity, or environmental factors, the risk of developing skin infections is increased. Although a large majority of bacterial associated skin infections are common, a portion can potentially manifest into clinically significant morbidity. For example, Gram-positive species that typically reside on the skin such as Staphylococcus and Streptococcus can cause numerous epidermal (impetigo, ecthyma) and dermal (cellulitis, necrotizing fasciitis, erysipelas) skin infections. Moreover, the increasing incidence of bacterial antibiotic resistance represents a serious challenge to modern medicine and threatens the health care system. Therefore, it is critical to develop tools and strategies that can allow us to better elucidate the nature and mechanism of bacterial virulence. To this end, mass spectrometry (MS)-based proteomics has been revolutionizing biomedical research, and has positively impacted the microbiology field. Advances in MS technologies have paved the way for numerous bacterial proteomes and their respective post translational modifications (PTMs) to be accurately identified and quantified in a high throughput and robust fashion. This technological platform offers critical information with regards to signal transduction, adherence, and microbial–host interactions associated with bacterial pathogenesis. This mini-review serves to highlight the current progress proteomics has contributed toward the understanding of bacteria that are associated with skin related diseases, infections, and antibiotic resistance.

Comprehensive profiling of lysine acetylproteome analysis reveals diverse functions of lysine acetylation in common wheat

Lysine acetylation of proteins, a dynamic and reversible post-translational modification, plays a critical regulatory role in both eukaryotes and prokaryotes. Several researches have been carried out on acetylproteome in plants. However, until now, there have been no data on common wheat, the major cereal crop in the world. In this study, we performed a global acetylproteome analysis of common wheat variety (Triticum aestivum L.), Chinese Spring. In total, 416 lysine modification sites were identified on 277 proteins, which are involved in a wide variety of biological processes. Consistent with previous studies, a large proportion of the acetylated proteins are involved in metabolic process. Interestingly, according to the functional enrichment analysis, 26 acetylated proteins are involved in photosynthesis and Calvin cycle, suggesting an important role of lysine acetylation in these processes. Moreover, protein interaction network analysis reveals that diverse interactions are modulated by protein acetylation. These data represent the first report of acetylome in common wheat and serve as an important resource for exploring the physiological role of lysine acetylation in this organism and likely in all plants.

A comprehensive catalog of the lysine-acetylation targets in rice (Oryza sativa) based on proteomic analyses

Lysine acetylation is a dynamic and reversible post-translational modification that plays an important role in the gene transcription regulation. Here, we report high quality proteome-scale data for lysine-acetylation (Kac) sites and Kac proteins in rice (Oryza sativa). A total of 1337 Kac sites in 716 Kac proteins with diverse biological functions and subcellular localizations were identified in rice seedlings. About 42% of the sites were predicted to be localized in the chloroplast. Seven putative acetylation motifs were detected. Phenylalanine, located in both the upstream and downstream of the Kac sites, is the most conserved amino acid surrounding the regions. In addition, protein interaction network analysis revealed that a variety of signaling pathways are modulated by protein acetylation. KEGG pathway category enrichment analysis indicated that glyoxylate and dicarboxylate metabolism, carbon metabolism, and photosynthesis pathways are significantly enriched. Our results provide an in-depth understanding of the acetylome in rice seedlings, and the method described here will facilitate the systematic study of how Kac functions in growth, development, and abiotic and biotic stress responses in rice and other plants.

BIOLOGICAL SIGNIFICANCE

Rice is one of the most important crops consumption and is a model monocot for research. In this study, we combined a highly sensitive immune-affinity purification method (used pan anti-acetyl-lysine antibody conjugated agarose for immunoaffinity acetylated peptide enrichment) with high-resolution LC-MS/MS. In total, we identified 1337 Kac sites on 716 Kac proteins in rice cells. Bioinformatic analysis of the acetylome revealed that the acetylated proteins are involved in a variety of cellular functions and have diverse subcellular localizations. We also identified seven putative acetylation motifs in the acetylated proteins of rice. In addition, protein interaction network analysis revealed that a variety of signaling pathways were modulated by protein acetylation. KEGG pathway category enrichment analysis indicated that glyoxylate and dicarboxylate metabolism, carbon metabolism, and photosynthesis pathways were significantly enriched. To our knowledge, the number of Kac sites we identified was 23-times greater and the number of Kac proteins was 16-times greater than in a previous report. Our results provide an in-depth understanding of the acetylome in rice seedlings, and the method described here will facilitate the systematic study of how Kac functions in growth, development and responses to abiotic and biotic stresses in rice or other plants.

Acetylome analysis reveals the involvement of lysine acetylation in biosynthesis of antibiotics in Bacillus amyloliquefaciens

Lysine acetylation is a major post-translational modification that plays an important regulatory role in almost every aspects in both eukaryotes and prokaryotes. Bacillus amyloliquefaciens, a Gram-positive bacterium, is very effective for the control of plant pathogens. However, very little is known about the function of lysine acetylation in this organism. Here, we conducted the first lysine acetylome in B. amyloliquefaciens through a combination of highly sensitive immune-affinity purification and high-resolution LC-MS/MS. Overall, we identified 3268 lysine acetylation sites in 1254 proteins, which account for 32.9% of the total proteins in this bacterium. Till date, this is the highest ratio of acetylated proteins that have been identified in bacteria. Acetylated proteins are associated with a variety of biological processes and a large fraction of these proteins are involved in metabolism. Interestingly, for the first time, we found that about 71.1% (27/38) and 78.6% (22/28) of all the proteins tightly related to the synthesis of three types of pepketides and five families of lipopeptides were acetylated, respectively. These findings suggest that lysine acetylation plays a critical role in the regulation of antibiotics biosynthesis. These data serves as an important resource for further elucidation of the physiological role of lysine acetylation in B. amyloliquefaciens.

Global profiling of lysine acetylation in human histoplasmosis pathogen Histoplasma capsulatum

Histoplasma capsulatum is the causative agent of human histoplasmosis, which can cause respiratory and systemic mycosis in immune-compromised individuals. Lysine acetylation, a protein posttranslational protein modification, is widespread in both eukaryotes and prokaryotes. Although increasing evidence suggests that lysine acetylation may play critical roles in fungus physiology, very little is known about its extent and function in H. capsulatum. To comprehensively profile protein lysine acetylation in H. capsulatum, we performed a global acetylome analysis through peptide prefractionation, antibody enrichment, and LC-MS/MS analysis, identifying 775 acetylation sites on 456 acetylated proteins; and functionally analysis showing their involvement in different biological processes. We defined six types of acetylation site motifs, and the results imply that lysine residue of polypeptide with tyrosine at the -1 and +1 positions, histidine at the +1 position, and phenylalanine (F) at the +1 and +2 position is a preferred substrate of lysine acetyltransferase. Moreover, some virulence factors candidates including calmodulin and DnaK are acetylated. In conclusion, our data set may serve as an important resource for the elucidation of associations between functional protein lysine acetylation and virulence in H. capsulatum.

Dynamic Protein Acetylation in Plant-Pathogen Interactions

Pathogen infection triggers complex molecular perturbations within host cells that results in either resistance or susceptibility. Protein acetylation is an emerging biochemical modification that appears to play central roles during host-pathogen interactions. To date, research in this area has focused on two main themes linking protein acetylation to plant immune signaling. Firstly, it has been established that proper gene expression during defense responses requires modulation of histone acetylation within target gene promoter regions. Second, some pathogens can deliver effector molecules that encode acetyltransferases directly within the host cell to modify acetylation of specific host proteins. Collectively these findings suggest that the acetylation level for a range of host proteins may be modulated to alter the outcome of pathogen infection. This review will focus on summarizing our current understanding of the roles of protein acetylation in plant defense and highlight the utility of proteomics approaches to uncover the complete repertoire of acetylation changes triggered by pathogen infection.

Top-Down Mass Spectrometry Analysis of Membrane-Bound Light-Harvesting Complex 2 from Rhodobacter sphaeroides

We report a top-down proteomic analysis of the membrane-bound peripheral light-harvesting complex LH2 isolated from the purple photosynthetic bacterium Rhodobacter sphaeroides. The LH2 complex is coded for by the puc operon. The Rb. sphaeroides genome contains two puc operons, designated puc1BAC and puc2BA. Although previous work has shown consistently that the LH2 β polypeptide coded by the puc2B gene was assembled into LH2 complexes, there are contradictory reports as to whether the Puc2A polypeptides are incorporated into LH2 complexes. Furthermore, post-translational modifications of this protein offer the prospect that it could coordinate bacteriochlorophyll a (Bchl a) by a modified N-terminal residue. Here, we describe the components of the LH2 complex on the basis of electron-capture dissociation fragmentation to confirm the identity and sequence of the protein's subunits. We found that both gene products of the β polypeptides are expressed and assembled in the mature LH2 complex, but only the Puc1A-encoded polypeptide α is observed here. The methionine of the Puc2B-encoded polypeptide is missing, and a carboxyl group is attached to the threonine at the N-terminus. Surprisingly, one amino acid encoded as an isoleucine in both the puc2B gene and the mRNA is found as valine in the mature LH2 complex, suggesting an unexpected and unusual post-translational modification or a specific tRNA recoding of this one amino acid.

Altered acetylation and succinylation profiles in Corynebacterium glutamicum in response to conditions inducing glutamate overproduction

The bacterium Corynebacterium glutamicum is utilized during industrial fermentation to produce amino acids such as L-glutamate. During L-glutamate fermentation, C. glutamicum changes the flux of central carbon metabolism to favor L-glutamate production, but the molecular mechanisms that explain these flux changes remain largely unknown. Here, we found that the profiles of two major lysine acyl modifications were significantly altered upon glutamate overproduction in C. glutamicum; acetylation decreased, whereas succinylation increased. A label-free semi-quantitative proteomic analysis identified 604 acetylated proteins with 1328 unique acetylation sites and 288 succinylated proteins with 651 unique succinylation sites. Acetylation and succinylation targeted enzymes in central carbon metabolic pathways that are directly related to glutamate production, including the 2-oxoglutarate dehydrogenase complex (ODHC), a key enzyme regulating glutamate overproduction. Structural mapping revealed that several critical lysine residues in the ODHC components were susceptible to acetylation and succinylation. Furthermore, induction of glutamate production was associated with changes in the extent of acetylation and succinylation of lysine, suggesting that these modifications may affect the activity of enzymes involved in glutamate production. Deletion of phosphotransacetylase decreased the extent of protein acetylation in nonproducing condition, suggesting that acetyl phosphate-dependent acetylation is active in C. glutamicum. However, no effect was observed on the profiles of acetylation and succinylation in glutamate-producing condition upon disruption of acetyl phosphate metabolism or deacetylase homologs. It was considered likely that the reduced acetylation in glutamate-producing condition may reflect metabolic states where the flux through acid-producing pathways is very low, and substrates for acetylation do not accumulate in the cell. Succinylation would occur more easily than acetylation in such conditions where the substrates for both acetylation and succinylation are limited. This is the first study investigating the acetylome and succinylome of C. glutamicum, and it provides new insight into the roles of acyl modifications in C. glutamicum biology.

Acylation of Biomolecules in Prokaryotes: a Widespread Strategy for the Control of Biological Function and Metabolic Stress

Acylation of biomolecules (e.g., proteins and small molecules) is a process that occurs in cells of all domains of life and has emerged as a critical mechanism for the control of many aspects of cellular physiology, including chromatin maintenance, transcriptional regulation, primary metabolism, cell structure, and likely other cellular processes. Although this review focuses on the use of acetyl moieties to modify a protein or small molecule, it is clear that cells can use many weak organic acids (e.g., short-, medium-, and long-chain mono- and dicarboxylic aliphatics and aromatics) to modify a large suite of targets. Acetylation of biomolecules has been studied for decades within the context of histone-dependent regulation of gene expression and antibiotic resistance. It was not until the early 2000s that the connection between metabolism, physiology, and protein acetylation was reported. This was the first instance of a metabolic enzyme (acetyl coenzyme A [acetyl-CoA] synthetase) whose activity was controlled by acetylation via a regulatory system responsive to physiological cues. The above-mentioned system was comprised of an acyltransferase and a partner deacylase. Given the reversibility of the acylation process, this system is also referred to as reversible lysine acylation (RLA). A wealth of information has been obtained since the discovery of RLA in prokaryotes, and we are just beginning to visualize the extent of the impact that this regulatory system has on cell function.

Changes in the Acetylome and Succinylome of Bacillus subtilis in Response to Carbon Source

Lysine residues can be post-translationally modified by various acyl modifications in bacteria and eukarya. Here, we showed that two major acyl modifications, acetylation and succinylation, were changed in response to the carbon source in the Gram-positive model bacterium Bacillus subtilis. Acetylation was more common when the cells were grown on glucose, glycerol, or pyruvate, whereas succinylation was upregulated when the cells were grown on citrate, reflecting the metabolic states that preferentially produce acetyl-CoA and succinyl-CoA, respectively. To identify and quantify changes in acetylation and succinylation in response to the carbon source, we performed a stable isotope labeling by amino acids in cell culture (SILAC)-based quantitative proteomic analysis of cells grown on glucose or citrate. We identified 629 acetylated proteins with 1355 unique acetylation sites and 204 succinylated proteins with 327 unique succinylation sites. Acetylation targeted different metabolic pathways under the two growth conditions: branched-chain amino acid biosynthesis and purine metabolism in glucose and the citrate cycle in citrate. Succinylation preferentially targeted the citrate cycle in citrate. Acetylation and succinylation mostly targeted different lysine residues and showed a preference for different residues surrounding the modification sites, suggesting that the two modifications may depend on different factors such as characteristics of acyl-group donors, molecular environment of the lysine substrate, and/or the modifying enzymes. Changes in acetylation and succinylation were observed in proteins involved in central carbon metabolism and in components of the transcription and translation machineries, such as RNA polymerase and the ribosome. Mutations that modulate protein acylation affected B. subtilis growth. A mutation in acetate kinase (ackA) increased the global acetylation level, suggesting that acetyl phosphate-dependent acetylation is common in B. subtilis, just as it is in Escherichia coli. Our results suggest that acyl modifications play a role in the physiological adaptations to changes in carbon nutrient availability of B. subtilis.

Proteomic profiling of lysine acetylation in Pseudomonas aeruginosa reveals the diversity of acetylated proteins

Protein lysine acetylation is a reversible and highly regulated post-translational modification with the well demonstrated physiological relevance in eukaryotes. Recently, its important role in the regulation of metabolic processes in bacteria was highlighted. Here, we reported the lysine acetylproteome of Pseudomonas aeruginosa using a proteomic approach. We identified 430 unique peptides corresponding to 320 acetylated proteins. In addition to the proteins involved in various metabolic pathways, several enzymes contributing to the lipopolysaccharides biosynthesis were characterized as acetylated. This data set illustrated the abundance and the diversity of acetylated lysine proteins in P. aeruginosa and opens opportunities to explore the role of the acetylation in the bacterial physiology.

Acetylome analysis reveals the involvement of lysine acetylation in photosynthesis and carbon metabolism in the model cyanobacterium Synechocystis sp. PCC 6803

Cyanobacteria are the oldest known life form inhabiting Earth and the only prokaryotes capable of performing oxygenic photosynthesis. Synechocystis sp. PCC 6803 (Synechocystis) is a model cyanobacterium used extensively in research on photosynthesis and environmental adaptation. Posttranslational protein modification by lysine acetylation plays a critical regulatory role in both eukaryotes and prokaryotes; however, its extent and function in cyanobacteria remain unexplored. Herein, we performed a global acetylome analysis on Synechocystis through peptide prefractionation, antibody enrichment, and high accuracy LC-MS/MS analysis; identified 776 acetylation sites on 513 acetylated proteins; and functionally categorized them into an interaction map showing their involvement in various biological processes. Consistent with previous reports, a large fraction of the acetylation sites are present on proteins involved in cellular metabolism. Interestingly, for the first time, many proteins involved in photosynthesis, including the subunits of phycocyanin (CpcA, CpcB, CpcC, and CpcG) and allophycocyanin (ApcA, ApcB, ApcD, ApcE, and ApcF), were found to be lysine acetylated, suggesting that lysine acetylation may play regulatory roles in the photosynthesis process. Six identified acetylated proteins associated with photosynthesis and carbon metabolism were further validated by immunoprecipitation and Western blotting. Our data provide the first global survey of lysine acetylation in cyanobacteria and reveal previously unappreciated roles of lysine acetylation in the regulation of photosynthesis. The provided data set may serve as an important resource for the functional analysis of lysine acetylation in cyanobacteria and facilitate the elucidation of the entire metabolic networks and photosynthesis process in this model cyanobacterium.

First succinyl-proteome profiling of extensively drug-resistant Mycobacterium tuberculosis revealed involvement of succinylation in cellular physiology

Protein lysine succinylation, an emerging protein post-translational modification widespread among eukaryotic and prokaryotic cells, represents an important regulator of cellular processes. However, the extent and function of lysine succinylation in Mycobacterium tuberculosis, especially extensively drug-resistant strain, remain elusive. Combining protein/peptide prefractionation, immunoaffinity enrichment, and LC-MS/MS analysis, a total of 686 succinylated proteins and 1739 succinylation sites of M. tuberculosis were identified, representing the first global profiling of M. tuberculosis lysine succinylation. The identified succinylated proteins are involved in a variety of cellular functions such as metabolic processes, transcription, translation, and stress responses and exhibit different subcellular localization via GO, protein interaction network, and other bioinformatic analysis. Notably, proteins involved in protein biosynthesis and carbon metabolism are preferred targets of lysine succinylation. Moreover, two prevalent sequence patterns: EK(suc) and K*****K(suc), can be found around the succinylation sites. There are 109 lysine-succinylated homologues in E. coli, suggesting highly conserved succinylated proteins. Succinylation was found to occur at the active sites predicted by Prosite signature including Rv0946c, indicating that lysine succinylation may affect their activities. There is extensive overlapping between acetylation sites and succinylation sites in M. tuberculosis. Many M. tuberculosis metabolic enzymes and antibiotic resistance proteins were succinylated. This study provides a basis for further characterization of the pathophysiological role of lysine succinylation in M. tuberculosis.