N-acetylation of α-synuclein enhances synaptic vesicle clustering mediated by α-synuclein and lysophosphatidylcholine

Post-translational modifications (PTMs) of α-synuclein (α-syn) such as acetylation and phosphorylation play important yet distinct roles in regulating α-syn conformation, membrane binding, and amyloid aggregation. However, how PTMs regulate α-syn function in presynaptic terminals remains unclear. Previously, we reported that α-syn clusters synaptic vesicles (SV) 1, and neutral phospholipid lysophosphatidylcholine (LPC) can mediate this clustering 2. Here, based on our previous findings, we further demonstrate that N-terminal acetylation, which occurs under physiological condition and is irreversible in mammalian cells, significantly enhances the functional activity of α-syn in clustering SVs. Mechanistic studies reveal that this enhancement is caused by the N-acetylation-promoted insertion of α-syn's N-terminus and increased intermolecular interactions on the LPC-containing membrane. Our work demonstrates that N-acetylation fine-tunes α-syn-LPC interaction for mediating α-syn's function in SV clustering.

The physiological effect of rimI/rimJ silencing by CRISPR interference in Mycobacterium smegmatis mc2155

N-terminal acetylation of proteins is an important post-translational modification (PTM) found in eukaryotes and prokaryotes. In bacteria, N-terminal acetylation is suggested to play various regulatory roles related to protein stability, gene expression, stress response, and virulence; however, the mechanism of such response remains unclear. The proteins, namely RimI/RimJ, are involved in N-terminal acetylation in mycobacteria. In this study, we used CRISPR interference (CRISPRi) to silence rimI/rimJ in Mycobacterium smegmatis mc²155 to investigate the physiological effects of N-terminal acetylation in cell survival and stress response. Repeat analysis of growth curves in rich media and biofilm analysis in minimal media of various mutant strains and wild-type bacteria did not show significant differences that could be attributed to the rimI/rimJ silencing. However, total proteome and acetylome profiles varied significantly across mutants and wild-type strains, highlighting the role of RimI/RimJ in modulating levels of proprotein acetylation in the cellular milieu. Further, we observed a significant increase in the minimum inhibitory concentration (MIC) (from 64 to 1024 µg ml^-1) for the drug isoniazid in rimI mutant strains. The increase in MIC value for the drug isoniazid in the mutant strains suggests the link between N-terminal acetylation and antibiotic resistance. The study highlights the utility of CRISPRi as a convenient tool to study the role of PTMs, such as acetylation in mycobacteria. It also identifies rimI/rimJ genes as necessary for managing cellular response against antibiotic stress. Further research would be required to decipher the potential of targeting acetylation to enhance the efficacy of existing antibiotics.

560G>A (rs4986782) (R187Q) Single Nucleotide Polymorphism in Arylamine N-Acetyltransferase 1 Increases Affinity for the Aromatic Amine Carcinogens 4-Aminobiphenyl and N-Hydroxy-4-Aminobiphenyl: Implications for Cancer Risk Assessment

Human arylamine N-acetyltransferase 1 (NAT1) catalyzes the N-acetylation of arylamine carcinogens such as 4-aminobiphenyl (ABP), and following N-hydroxylation, the O-acetylation of N-hydroxy-arylamine carcinogens such as N-hydroxy-ABP (N-OH-ABP). Genetic polymorphisms in NAT1 are linked to cancer susceptibility following exposures. The effects of individual single nucleotide polymorphisms (SNPs) in the NAT1 coding exon on Michaelis-Menten kinetic constants was assessed for ABP N-acetyltransferase and N-OH-ABP O-acetyltransferase activity following transfection of human NAT1 into COS-1 cells (SV40-transformed African green monkey kidney cells). NAT1 coding region SNPs 97C > T (rs56318881) (R33stop), 190C > T (rs56379106) (R64W), 559C > T (rs5030839) (R187stop) and 752A > T (rs56172717) (D251V) reduced ABP N- acetyltransferase and N-OH-ABP O-acetyltransferase activity below detection. 21T > G (rs4986992) (synonymous), 402T > C (rs146727732) (synonymous), 445G > A (rs4987076) (V149I), 613A > G (rs72554609) (M205V) and 640T > G (rs4986783) (S241A) did not significantly affect Vmax for ABP N-acetyltransferase or N-OH-ABP O-acetyltransferase. 781G > A (rs72554610) (E261K), and 787A > G (rs72554611) (I263V) slightly reduced ABP N-acetyltransferase and N-OH-ABP O-acetyltransferase activities whereas 560G > A (rs4986782) (R187Q) substantially and significantly reduced them. 560G > A (rs4986782) (R187Q) significantly reduced the apparent Km for ABP and N-OH-ABP a finding that was not observed with any of the other NAT1 SNPs tested. These findings suggest that the role of the 560G > A (rs4986782) (R187Q) SNP cancer risk assessment may be modified by exposure level to aromatic amine carcinogens such as ABP.

Chemical Approaches to Prepare Modified Heparin and Heparosan Polymers for Biological Studies

Heparin is a potent clinically used anticoagulant. It is a heterogeneous mixture of polymers that contain a variety of sulfation patterns. Heparin polymers carrying rare 3-O-sulfated glucosamine units have been proven to be critical for binding to antithrombin and elicit an anticoagulant response. Heparins with other sulfation patterns are able to bind to a variety of other proteins such as FGF, VEGF, and CXCL-3. By modulating heparin's sulfation pattern, it is possible to generate polymers that can regulate biological processes beyond hemostasis. In this chapter, we describe a variety of chemical modification methods, including N-acetylation, N-deacetylation, N-sulfation, O-sulfation, selective 2-O desulfation, and complete desulfation, to prepare heparin-like polymers with distinct sulfation patterns for conducting biological studies.

Urine Metabolite Levels, Adverse Kidney Outcomes, and Mortality in CKD Patients: A Metabolome-wide Association Study

RATIONALE & OBJECTIVE

Mechanisms underlying the variable course of disease progression in patients with chronic kidney disease (CKD) are incompletely understood. The aim of this study was to identify novel biomarkers of adverse kidney outcomes and overall mortality, which may offer insights into pathophysiologic mechanisms.

STUDY DESIGN

Metabolome-wide association study.

SETTING & PARTICIPANTS

5,087 patients with CKD enrolled in the observational German Chronic Kidney Disease Study.

EXPOSURES

Measurements of 1,487 metabolites in urine.

OUTCOMES

End points of interest were time to kidney failure (KF), a combined end point of KF and acute kidney injury (KF+AKI), and overall mortality.

ANALYTICAL APPROACH

Statistical analysis was based on a discovery-replication design (ratio 2:1) and multivariable-adjusted Cox regression models.

RESULTS

After a median follow-up of 4 years, 362 patients died, 241 experienced KF, and 382 experienced KF+AKI. Overall, we identified 55 urine metabolites whose levels were significantly associated with adverse kidney outcomes and/or mortality. Higher levels of C-glycosyltryptophan were consistently associated with all 3 main end points (hazard ratios of 1.43 [95% CI, 1.27-1.61] for KF, 1.40 [95% CI, 1.27-1.55] for KF+AKI, and 1.47 [95% CI, 1.33-1.63] for death). Metabolites belonging to the phosphatidylcholine pathway showed significant enrichment. Members of this pathway contributed to the improvement of the prediction performance for KF observed when multiple metabolites were added to the well-established Kidney Failure Risk Equation.

LIMITATIONS

Findings among patients of European ancestry with CKD may not be generalizable to the general population.

CONCLUSIONS

Our comprehensive screen of the association between urine metabolite levels and adverse kidney outcomes and mortality identifies metabolites that predict KF and represents a valuable resource for future studies of biomarkers of CKD progression.

Influence of N-acetyltransferase 2 gene polymorphisms on the in vitro metabolism of the epidermal growth factor receptor inhibitor rociletinib

AIMS

Rociletinib showed activity in T790M-positive non-small cell lung cancer patients. It undergoes amide hydrolysis to form M502, followed by N-acetylation to M544 or amide hydrolysis to M460. We identified the enzymes responsible for rociletinib metabolism, and investigated the relationship between M544 formation and N-acetyltransferase 2 (NAT2) polymorphisms.

METHODS

Rociletinib and metabolites were incubated with carboxylesterase (CES)1b, CES1c, CES2, NAT1, NAT2, arylacetamide deacetylase, inhibitors, pooled human liver microsomes (HLM) and cytosols (HLC). Cytosols (n = 107) were genotyped for NAT2 polymorphisms (rs1041983 and rs1801280) and incubated with M502. Human hepatocytes from intermediate (NAT2*6/*12A) and slow (NAT2*5B/*5B) acetylators were incubated with 10 μM rociletinib and metabolites for 24 hours. Metabolites were measured by high-performance liquid chromatography.

RESULTS

M502 was formed from rociletinib and M544 by CES2 and HLM; M544 and N-acetyl-M460 were formed by NAT2 and HLC; M460 was not formed by CES or arylacetamide deacetylase. M502 formation by HLM was inhibited by bis-(4-nitrophenyl)phosphate and eserine (10 μM). M544 formation in HLC was inhibited by 100 μM quercetin and was associated with NAT2 genotype (P < .0001). M460 formation in HLM was inhibited by eserine, and M460 was N-acetylated in HLC. Hepatocytes formed M502, M544 and M460. The intermediate acetylator showed higher production (range: 3.4-5.1-fold) of N-acetylated metabolites than the slow acetylator.

CONCLUSIONS

Results indicate that NAT2 and CES2 are involved in rociletinib metabolism, and polymorphic NAT2 could alter drug exposure in patients. Slow NAT2 acetylators would have higher exposure to M502 and M460 and consequently, be at increased risk of experiencing hyperglycaemia and QTc prolongation.

Avidity within the N-terminal anchor drives α-synuclein membrane interaction and insertion

In the brain, α-synuclein (aSN) partitions between free unbound cytosolic and membrane bound forms modulating both its physiological and pathological role and complicating its study due to structural heterogeneity. Here, we use an interdisciplinary, synergistic approach to characterize the properties of aSN:lipid mixtures, isolated aSN:lipid co-structures, and aSN in mammalian cells. Enabled by the isolation of the membrane-bound state, we show that within the previously described N-terminal membrane anchor, membrane interaction relies both on an N-terminal tail (NTT) head group layer insertion of 14 residues and a folded-upon-binding helix at the membrane surface. Both binding events must be present; if, for example, the NTT insertion is lost, the membrane affinity of aSN is severely compromised and formation of aSN:lipid co-structures hampered. In mammalian cells, compromised cooperativity results in lowered membrane association. Thus, avidity within the N-terminal anchor couples N-terminal insertion and helical surface binding, which is crucial for aSN membrane interaction and cellular localization, and may affect membrane fusion.

Navigating the dynamic landscape of alpha-synuclein morphology: a review of the physiologically relevant tetrameric conformation

N-acetylated α-synuclein (αSyn) has long been established as an intrinsically disordered protein associated with a dysfunctional role in Parkinson's disease. In recent years, a physiologically relevant, higher order conformation has been identified as a helical tetramer that is tailored by buried hydrophobic interactions and is distinctively aggregation resistant. The canonical mechanism by which the tetramer assembles remains elusive. As novel biochemical approaches, computational methods, pioneering purification platforms, and powerful imaging techniques continue to develop, puzzling information that once sparked debate as to the veracity of the tetramer has now shed light upon this new counterpart in αSyn neurobiology. Nuclear magnetic resonance and computational studies on multimeric αSyn structure have revealed that the protein folding propensity is controlled by small energy barriers that enable large scale reconfiguration. Alternatively, familial mutations ablate tetramerization and reconfigure polymorphic fibrillization. In this review, we will discuss the dynamic landscape of αSyn quaternary structure with a focus on the tetrameric conformation.

Identification of a metabolic disposal route for the oncometabolite S-(2-succino)cysteine in Bacillus subtilis

Cellular thiols such as cysteine spontaneously and readily react with the respiratory intermediate fumarate, resulting in the formation of stable S-(2-succino)-adducts. Fumarate-mediated succination of thiols increases in certain tumors and in response to glucotoxicity associated with diabetes. Therefore, S-(2-succino)-adducts such as S-(2-succino)cysteine (2SC) are considered oncometabolites and biomarkers for human disease. No disposal routes for S-(2-succino)-compounds have been reported prior to this study. Here, we show that Bacillus subtilis metabolizes 2SC to cysteine using a pathway encoded by the yxe operon. The first step is N-acetylation of 2SC followed by an oxygenation that we propose results in the release of oxaloacetate and N-acetylcysteine, which is deacetylated to give cysteine. Knockouts of the genes predicted to mediate each step in the pathway lose the ability to grow on 2SC as the sulfur source and accumulate the expected upstream metabolite(s). We further show that N-acetylation of 2SC relieves toxicity. This is the first demonstration of a metabolic disposal route for any S-(2-succino)-compound, paving the way toward the identification of corresponding pathways in other species.

Differential association for N-acetyltransferase 2 genotype and phenotype with bladder cancer risk in Chinese population

BACKGROUND

N-acetyltransferase 2 (NAT2) is involved in both carcinogen detoxification through hepatic N-acetylation and carcinogen activation through local O-acetylation. NAT2 slow acetylation status is significantly associated with increased bladder cancer risk among European populations, but its association in Asian populations is inconclusive.

METHODS

NAT2 acetylation status was determined by both single nucleotide polymorphisms (SNPs) and caffeine metabolic ratio (CMR), in a population-based study of 494 bladder cancer patients and 507 control subjects in Shanghai, China.

RESULTS

The CMR, a functional measure of hepatic N-acetylation, was significantly reduced in a dose-dependent manner among both cases and controls possessing the SNP-inferred NAT2 slow acetylation status (all P-values<5.0×10-10). The CMR-determined slow N-acetylation status (CMR<0.34) was significantly associated with a 50% increased risk of bladder cancer (odds ratio = 1.50, 95% confidence interval = 1.10-2.06) whereas the SNP-inferred slow acetylation statuses were significantly associated with an approximately 50% decreased risk of bladder cancer. The genotype-disease association was strengthened after the adjustment for CMR and was primarily observed among never smokers.

CONCLUSIONS

The apparent differential associations for phenotypic and genetic measures of acetylation statuses with bladder cancer risk may reflect dual functions of NAT2 in bladder carcinogenesis because the former only measures the capacity of carcinogen detoxification pathway while the latter represents both carcinogen activation and detoxification pathways. Future studies are warranted to ascertain the specific role of N- and O-acetylation in bladder carcinogenesis, particularly in populations exposed to different types of bladder carcinogens.

Role of N-acetyltransferase 2 acetylation polymorphism in 4, 4'-methylene bis (2-chloroaniline) biotransformation

Arylamine N-acetyltransferase 1 (NAT1) and 2 (NAT2) catalyze the acetylation of arylamine carcinogens. Single nucleotide polymorphisms in the NAT2 coding exon present in NAT2 haplotypes encode allozymes with reduced N-acetyltransferase activity towards the N-acetylation of arylamine carcinogens and the O-acetylation of their N-hydroxylated metabolites. NAT2 acetylator phenotype modifies urinary bladder cancer risk following exposures to arylamine carcinogens such as 4-aminobiphenyl. 4, 4'-methylene bis (2-chloroaniline) (MOCA) is a Group 1 carcinogen for which a role of the NAT2 acetylation polymorphism on cancer risk is unknown. We investigated the role of NAT2 and the genetic acetylation polymorphism on both MOCA N-acetylation and N-hydroxy-MOCA O-acetylation. MOCA N-acetylation exhibited a robust gene dose response in rabbit liver cytosol and in cryopreserved human hepatocytes derived from individuals of rapid, intermediate and slow acetylator NAT2 genotype. MOCA exhibited about 4-fold higher affinity for recombinant human NAT2 than NAT1. Recombinant human NAT2*4 (reference) and 15 variant recombinant human NAT2 allozymes catalyzed both the N-acetylation of MOCA and the O-acetylation of N-hydroxy-MOCA. Human NAT2 5, NAT2 6, NAT2 7 and NAT2 14 allozymes catalyzed MOCA N-acetylation and N-hydroxy-O-acetylation at rates much lower than the reference NAT2 4 allozyme. In conclusion, our results show that NAT2 acetylator genotype has an important role in MOCA metabolism and suggest that risk assessments related to MOCA exposures consider accounting for NAT2 acetylator phenotype in the analysis.

N-terminal acetylation and replicative age affect proteasome localization and cell fitness during aging

Specific degradation of proteins is essential for virtually all cellular processes and is carried out predominantly by the proteasome. The proteasome is important for clearance of damaged cellular proteins. Damaged proteins accumulate over time and excess damaged proteins can aggregate and induce the death of old cells. In yeast, the localization of the proteasome changes dramatically during aging, possibly in response to altered proteasome activity requirements. We followed two key parameters of this process: the distribution of proteasomes in nuclear and cytosolic compartments, and the formation of cytoplasmic aggregate-like structures called proteasome storage granules (PSGs). Whereas replicative young cells efficiently relocalized proteasomes from the nucleus to the cytoplasm and formed PSGs, replicative old cells were less efficient in relocalizing the proteasome and had less PSGs. By using a microscopy-based genome-wide screen, we identified genetic factors involved in these processes. Both relocalization of the proteasome and PSG formation were affected by two of the three N-acetylation complexes. These N-acetylation complexes also had different effects on the longevity of cells, indicating that each N-acetylation complex has different roles in proteasome location and aging.

Furan-based acetylating agent for the chemical modification of proteins

We have synthesized a furan-based acetylating agent, 2,5-bisacetoxymethylfuran (BAMF) from carbohydrate derived 5-hydroxymethylfurfural (HMF) and studied its acetylation activity with amines and cytochrome c. The results show that BAMF can modify proteins in biological conditions without affecting their structure and function. The modification of cytochrome c with BAMF occurred through the reduction of heme center, but there was no change in the coordination property of iron and the tertiary structure of cytochrome c. Further analysis using MALDI-TOF-MS spectrometer suggests that BAMF selectively targeted lysine amino acid of cytochrome c under our experimental conditions. Kinetics study revealed that the modification of cytochrome c with BAMF took place at faster rates than aspirin.

Characterization of N-terminal protein modifications in Pseudomonas aeruginosa PA14

Even though protein initiator methionine excision (NME) and N-terminal acetylation (NTA) have been relatively well investigated in eukaryotic proteomes, few studies were dedicated to these modifications in bacteria up to now. In this work, we investigated, for the first time, the N-terminal proteome of the bacterium Pseudomonas aeruginosa PA14 by studying the NME and NTA processes using proteomic approaches. For NME, most of proteins had their initiator Met cleaved (63%) and the nature of the penultimate residue seems to be essential for this cleavage. Concerning NTA, two methods were applied (protein fractionation and peptide enrichment). This allowed us to identify 117 Nα-acetylated proteins, among them 113 have not yet been described as modified in bacteria. Most often, the non-acetylated form was over-represented compared to the acetylated form, arguing that this latter was a minor part of the total abundance of a given protein. Furthermore, some proteins with acetylated initiator methionine were observed. The present work significantly enlarges the number of N-terminally modified proteins in bacteria and confirms that these modifications are a general and fundamental process, not only restricted to eukaryotes.

BIOLOGICAL SIGNIFICANCE

Protein modifications in prokaryotes have been detected more recently than in eukaryotes. Methionine cleavage and N-terminal acetylation are two common protein N-terminal modifications. Despite their importance in bacterial processes, they are less investigated. The characterization of N-terminal acetylation in bacteria is a challenge because no antibody exists and it is a less frequent modification than in eukaryotes. We used proteomic approaches (enrichment, fractionation, nanoLC-MS/MS, and bioinformatic analyses) to investigate the N-terminal methionine excision and to profile the N-terminal acetylome of P. aeruginosa strain PA14. From our results, around 60% of the proteins had their iMet cleaved. In total, 117 proteins were identified constituting the largest dataset in prokaryotes. Among them, proteins kept their initiator methionine and were acetylated. These results may facilitate the design of experiments to better understand the role of acetylation at the protein N-terminus of P. aeruginosa PA14.

Human disposition, metabolism and excretion of etamicastat, a reversible, peripherally selective dopamine β-hydroxylase inhibitor

AIMS

Etamicastat is a reversible dopamine-β-hydroxylase inhibitor that decreases noradrenaline levels in sympathetically innervated tissues and slows down sympathetic nervous system drive. In this study, the disposition, metabolism and excretion of etamicastat were evaluated following [(14)C]-etamicastat dosing.

METHODS

Healthy Caucasian males (n = 4) were enrolled in this single-dose, open-label study. Subjects were administered 600 mg of unlabelled etamicastat and 98 µCi weighing 0.623 mg [(14)C]-etamicastat. Blood samples, urine and faeces were collected to characterize the disposition, excretion and metabolites of etamicastat.

RESULTS

Eleven days after administration, 94.0% of the administered radioactivity had been excreted; 33.3 and 58.5% of the administered dose was found in the faeces and urine, respectively. Renal excretion of unchanged etamicastat and its N-acetylated metabolite (BIA 5-961) accounted for 20.0 and 10.7% of the dose, respectively. Etamicastat and BIA 5-961 accounted for most of the circulating radioactivity, with a BIA 5-961/etamicastat ratio that was highly variable both for the maximal plasma concentration (19.68-226.28%) and for the area under the plasma concentration-time curve from time zero to the last sampling time at which the concentration was above the limit of quantification (15.82- 281.71%). Alongside N-acetylation, metabolism of etamicastat also occurs through oxidative deamination of the aminoethyl moiety, alkyl oxidation, desulfation and glucuronidation.

CONCLUSIONS

Etamicastat is rapidly absorbed, primarily excreted via urine, and its biotransformation occurs mainly via N-acetylation (N-acetyltransferase type 2), although glucuronidation, oxidation, oxidative deamination and desulfation also take place.