Potential Role of Lysine Acetylation in Antibiotic Resistance of Escherichia coli.

Antibiotic resistance is increasingly becoming a challenge to public health. The regulation of bacterial metabolism by post-translational modifications (PTMs) has been widely studied. However, the mechanism underlying the regulation of acetylation in bacterial resistance to antibiotics is still unknown. Here, we performed a quantitative analysis of the acetylated proteome of a wild-type (WT) Escherichia coli (E. coli) sensitive strain and ampicillin- (Re-Amp), kanamycin- (Re-Kan), and polymyxin B-resistant (Re-Pol) strains. Based on bioinformatics analysis combined with biochemical validations, we found a common regulatory mechanism between the different resistant strains. Our results showed that protein acetylation negatively regulates bacterial metabolism to regulate antibiotic resistance and positively regulates bacterial motility. Further analyses revealed that key enzymes in various metabolic pathways were differentially acetylated. In particular, pyruvate kinase (PykF), a glycolytic enzyme that regulates bacterial metabolism, and its acetylated form were highly expressed in the three resistant strains and were identified as reversibly acetylated by the deacetylase CobB and the acetyl-transferase PatZ (peptidyl-lysine N-acetyltransferase). Results showed that PykF also could be acetylated by nonenzymatic acetyl phosphatase (AcP) in vitro. Furthermore, the deacetylation of Lys413 in PykF increased PykF enzymatic activity by changing the conformation of its ATP binding site, resulting in an increase in energy production which, in turn, increased the sensitivity of drug-resistant strains to antibiotics. This study provides novel insights for understanding bacterial resistance and lays the foundation for future research on the regulation of acetylation in antibiotic-resistant strains. IMPORTANCE The misuse of antibiotics has resulted in the emergence of many antibiotic-resistant strains which seriously threaten human health. Protein post-translational modifications, especially acetylation, tightly control bacterial metabolism. However, the comprehensive mechanism underlying the regulation of acetylation in bacterial resistance remains unexplored. Here, acetylation was found to positively regulate bacterial motility and negatively regulate energy metabolism, which was common in all antibiotic-resistant strains. Moreover, the acetylation and deacetylation process of PykF was uncovered, and deacetylation of the Lys 413 in PykF was found to contribute to bacterial sensitivity to antibiotics. This study provides a new direction for research on the development of bacterial resistance through post-translational modifications and a theoretical basis for developing antibacterial drugs.

The mechanism of iron-compensation for manganese deficiency of Streptococcus pneumoniae.

Given their involvement in catalysis, infection, and biofilm formation, Fe and Mn are essential for bacterial survival and virulence. In this study, we found that Streptococcus pneumoniae (S. pneumoniae) could grow in the Mn-deficient medium (MDCM). Furthermore, findings showed that the Fe concentration in the bacterium increased when the Mn concentration decreased. In addition, it was noted that supplementing MDCM with Fe resulted in the recovery of bacterial growth. Quantitative proteomics using stable-isotope dimethyl labeling was performed to investigate the adaptive growth mechanism of S. pneumoniae under Mn-deficient conditions. It was found that the expression levels of 25 proteins were downregulated, whereas those of 54 proteins were upregulated in S. pneumoniae grown in MDCM. It was also noted that several of the downregulated proteins were involved in cell energy metabolism, amino acid synthesis, and reduction of oxidation products. More importantly, several ATP-binding cassette transporters related to Fe uptake, such as PiuA, PiaA, PitA, and SPD_1609, were overexpressed for increased Fe uptake from the MDCM. The results suggest that Mn deficiency disturbs multiple metabolic processes in S. pneumoniae. Furthermore, it causes a compensatory effect of Fe for Mn, which is beneficial for the survival of the bacterium in extreme environments. SIGNIFICANCE: The relationship between manganese and iron metabolism in S. pneumoniae has not been clearly revealed. In this paper, we suggest that Mn limitation disturbs multiple metabolic processes and evidently decreases the ATP level in the bacterium. In order to survive in this extreme environment, bacteria upregulated three type of Fe ion transporters PiuABC (heme), PiaABC (ferrichrome) and PitABC (Fe3+) to uptake enough Fe ions to response to Mn deficiency. Therefore, this study reveals a bacterial mechanism of Fe compensation for Mn, and provides new insight for investigating the relativeness of Fe and Mn metabolism of bacteria.

Comprehensive analysis of the lysine acetylome and its potential regulatory roles in the virulence of Streptococcus pneumoniae.

Protein lysine acetylation is a well-known modification with vital regulatory roles in various biological processes. Currently, the acetylated proteome in Streptococcus pneumoniae (S. pneumoniae) is not yet clear. Combining immune-affinity enrichment with mass spectrometry-based proteomics, we identified the first lysine acetylome of S. pneumoniae. In total, 653 lysine acetylated sites on 392 proteins were identified, which are involved in diverse important biological pathways, including gene expression and central metabolism. S. pneumoniae has a relatively high acetylation level, implying its prominent and diverse roles in the regulation of biological processes. In the acetylome of S. pneumoniae, the most frequently occurring motifs of acetylation are KacK, KacR, KacxK, KacxxK and KacH. Compared with the reported acetylation motifs in various bacterial species, the motif unique to S. pneumoniae is KacT, indicating that species-specific characteristics, regulations and molecular mechanisms of acetylation may exist in this bacterium. Notably, many proteins directly or indirectly contributing to virulence are prevalently acetylated, suggesting that acetylation may coordinate bacterial virulence. This work presented here provides the first system-wide analysis of lysine acetylation in Streptococcus species, which may facilitate a deeper understanding on the regulatory roles of acetylation in the bacteria. BIOLOGICAL SIGNIFICANCE: S. pneumoniae causes a series of serious human diseases. Protein acetylation regulates many important biological pathways in bacteria. In this study, the first lysine acetylome of S. pneumoniae was identified and comprehensively analyzed with bioinformatics methods. One unique acetylated motif (KacT) was identified, suggesting that specific characteristics of lysine acetylation reaction may exist in S. pneumoniae. Besides, our data suggest that lysine acetylation closely regulates bacterial virulence. Further study focusing on the biological functions of these acetylproteins may provide important clues for the therapy of S. pneumoniae infection.

An FGF8b-mimicking peptide with potent antiangiogenic activity.

Fibroblast growth factor (FGF) 8b interacts with its receptors and promotes angiogenesis in hormone­dependent tumors. In the present study, we demonstrated that a short peptide, termed 8b­13, which mimics part of the FGF8b structure, significantly inhibited the proliferation and migration of human umbilical vein endothelial cells (HUVECs) triggered by FGF8b using 3­(4,5­dimethylthiazol­2­yl)­2,5­diphenyltetrazolium bromide (MTT), flow cytometry and an in vitro scratch assay. In addition, the findings from western blotting and reverse transcription­quantitative polymerase chain reaction revealed that 8b­13 appeared to counteract the effects of FGF8b on the expression of cyclin D1, the activation of signaling cascades, and the expression of proangiogenic factors; these actions may be involved in the mechanism underlying the inhibitory effects of 8b­13 on FGF8b­induced HUVEC proliferation and migration. The present results suggested that 8b­13 may be considered a potent FGF8b antagonist with antiangiogenic activity, and may have potential as a novel therapeutic agent for the treatment of cancer characterized by abnormal FGF8b upregulation.