ITRAQ-coupled 2-D LC-MS/MS analysis of membrane protein profile in Escherichia coli incubated with apidaecin IB.
ABSTRACT: Apidaecins are a series of proline-rich, 18- to 20-residue antimicrobial peptides produced by insects. They are predominantly active against the gram-negative bacteria. Previous studies mainly focused on the identification of their internal macromolecular targets, few addressed on the action of apidaecins on the molecules, especially proteins, of bacterial cell membrane. In this study, iTRAQ-coupled 2-D LC-MS/MS technique was utilized to identify altered membrane proteins of Escherichia coli cells incubated with one isoform of apidaecins--apidaecin IB. Cell division protease ftsH, an essential regulator in maintenance of membrane lipid homeostasis, was found to be overproduced in cells incubated with apidaecin IB. Its over-expression intensified the degradation of cytoplasmic protein UDP-3-O-acyl-N- acetylglucosamine deacetylase, which catalyzes the first committed step in the biosynthesis of the lipid A moiety of LPS, and thus leaded to the further unbalanced biosynthesis of LPS and phospholipids. Our findings suggested a new antibacterial mechanism of apidaecins and perhaps, by extension, for other proline-rich antimicrobial peptides.
Project description:Drug resistance is a major problem in antibacterial chemotherapy. Apidaecins, which refer to a series of small, proline-rich antimicrobial peptides, are predominantly active against many drug-resistant bacteria. The apidaecins have special antibacterial mechanisms, and are non-toxic for human cells, a prerequisite for using them as novel antibiotic drugs. However, no efficient non-tagged apidaecin expression system has been reported, which is the limiting factor for their application. Here we successfully generated a Pichia pastoris transformant expressing and secreting apidaecin. However, expression was unstable and poor. Analysis of this revealed that the integration plasmid was frequently lost and that apidaecin expression resulted in cell death. Using N-methyl-N-nitro-N-nitroso-guanidine mutagenesis and selection, a mutant strain Apmu4 was derived, in which the rate of loss of the integration plasmid was much lower after induction, and which produced improved titres of apidaecin. Additionally, we discovered that using glucose as the sole carbon source to pre-culture the strain before induction could greatly enhance apidaecin production. A pilot-scale 10?L fermentation yielded 418?mg/L of recombinant apidaecin, which represents the highest reported yield of apidaecin. Consequently, this study reports the first super heterologous expression and secretion of apidaecin in yeast.
Project description:Proline-rich antimicrobial peptides (PrAMPs) represent promising alternative therapeutic options for the treatment of multidrug-resistant bacterial infections. PrAMPs are predominantly active against Gram-negative bacteria by inhibiting protein expression via at least two different modes of action, i.e., blocking the ribosomal exit tunnel of 70S ribosomes (oncocin-type binding) or inhibiting the assembly of the 50S ribosomal subunit (apidaecin-type binding). The in vivo efficacy and favorable biodistribution of oncocins confirmed the therapeutic potential of short PrAMPs for the first time, whereas the in vivo evaluation of apidaecins is still limited despite the promising efficacy of apidaecin-analog Api88 in an intraperitoneal murine infection model. Here, the in vivo efficacy of apidaecin-analog Api137 was studied, which rescued all NMRI mice from a lethal intraperitoneal infection with E. coli ATCC 25922 when administered three times intraperitoneal at doses of 0.6 mg/kg starting 1 h after infection. When Api88 and Api137 were administered intravenous or intraperitoneal at doses of 5 and 20 mg/kg, their plasma levels were similarly low (<3 ?g/mL) and four-fold lower than for oncocin-analog Onc72. This contradicted earlier expectation based on the very low serum stability of Api88 with a half-life time of only ~5 min compared to ~6 and ~3 h for Api137 and Onc72, respectively. Pharmacokinetic data relying on a sensitive mass spectrometry method utilizing multiple reaction monitoring and isotope-labeled peptides revealed that Api88 and Api137 were present in blood, urine, and kidney, and liver homogenates at similar levels accompanied by the same major metabolites comprising residues 1-16 and 1-17. The pretended discrepancy was solved, when all peptides were incubated in peritoneal lavage. Api137 was rapidly degraded at the C-terminus, while Api88 was rather stable despite releasing the same degradation products. Onc72 was very stable explaining its higher plasma levels compared to Api88 and Api137 after intraperitoneal administration illuminating its good in vivo efficacy. The data indicate that the degradation of therapeutic peptides should be studied in serum and further body fluids. Moreover, the high efficacy in murine infection models and the fast clearance of Api88 and Api137 within ~60 min after intravenous and ~90 min after intraperitoneal injections indicate that their in vivo efficacy relates to the maximal peptide concentration achieved in blood.
Project description:The conjugation of the cationic antimicrobial peptide, apidaecin Ib, to the anionic photosensitizer, 5(4'-carboxyphenyl)-10,15,20-triphenylporphyrin (cTPP), afforded a new antibacterial agent effective, under light activation, against both Gram-positive and Gram-negative bacteria. At low concentrations (1.5-15 ?M) the conjugate was able to reduce the survival of Escherichia coli cells by 3-4 log10, and most notably, it resulted photoactive also against hard-to-treat Pseudomonas aeruginosa, although at higher concentration (60 ?M). Under similar conditions, the photosensitizer alone was only photoactive against Staphylococcus aureus while the unconjugated peptide was inactive against all the bacterial strains tested. This study shows the possibility of obtaining new broad-spectrum apidaecin-photosensitizer conjugates with potent antibacterial activity.
Project description:We investigated the importance of protein nutrition for honey bee immunity. Different protein diets (monofloral pollen of Helianthus spp., Sinapis spp., Asparagus spp., Castanea spp., a mixture of the four different pollen and the pollen substitute FeedbeeTM) were fed to honey bees in cages ad libitum. After 18 days of feeding, apidaecin 1 isoforms concentration in the thorax were measured using nanoflow liquid chromatography coupled with mass spectrometry. Expression levels of genes, coding for apidaecins and abaecin in the abdomen were determined using quantitative PCR. The results indicate that protein-containing nutrition in adult worker honey bees can trigger certain metabolic responses. Bees without dietary protein showed lower apidaecin 1 isoforms concentrations. The significantly lowest concentration of apidaecin 1 isoforms was found in the group that was fed no pollen diet when compared to Asparagus, Castanea, Helianthus, and Sinapis pollen or the pollen supplement FeedBeeTM. Expression levels of the respective genes were also affected by the protein diets and different expression levels of these two antimicrobial peptides were found. Positive correlation between concentration and gene expression of apidaecins was found. The significance of feeding bees with different protein diets, as well as the importance of pollen nutrition for honey bee immunity is demonstrated.
Project description:Identifying the target molecules of antimicrobial agents is essential for assessing their mode of action. Here, we propose Acquired Resistance induced by Gene Overexpression (ARGO) as a novel in vivo approach for exploring target proteins of antimicrobial agents. The principle of the method is based on the fact that overexpression of the expected target protein leads to reduced sensitivity to the antimicrobial agent. We applied this approach to identify target proteins of the antimicrobial peptide apidaecin, which is specifically effective against Gram-negative bacteria. To this end, a set of overexpression Escherichia coli clones was tested, and peptide chain release factor 1, which directs the termination of translation, was found as a candidate, suggesting that apidaecin inhibits the termination step of translation. This finding was confirmed in vivo and in vitro by evaluating the inhibitory activity of apidaecin towards lacZ reporter gene expression, which is tightly dependent on its stop codon. The results of this study demonstrate that apidaecin exerts its antimicrobial effects partly by inhibiting release factors.
Project description:Apidaecins are cationic, proline-rich antimicrobial peptides originally isolated from honeybees and exhibit high Gram-negative activity by inhibiting bacterial protein translation. Pharmacokinetics of apidaecin derivative Api137 was studied using single and multiple intravenous or subcutaneous injections as well as continuous subcutaneous infusion and correlated to its efficacy in a lethal murine Escherichia coli infection model. Survival rates of infected CD-1 mice were monitored and Api137 and its metabolites were quantified in plasma of uninfected CD-1 mice and Sprague Dawley rats using reversed-phase chromatography coupled online to mass spectrometry. The highest Api137 plasma levels of 23 mg/L were obtained after a single intravenous injection of 20 mg/kg body weight, which declined fast over the next 120 min (half-life time < 30 min). In contrast, continuous subcutaneous infusion of a similar dose over an hour (19.2 mg/kg/h) lead to stable plasma levels of ?6 mg/L, which was above the minimal inhibitory concentration against E. coli ATCC 25922 (4 mg/L). The increased exposure by continuous subcutaneous administration of Api137 at 19.2 mg/kg/h over 48 h improved efficacy in the murine intraperitoneal sepsis model with survival rates of 67% over 5 days compared to 33% after intravenous and subcutaneous administration in different dosing schemes. To the best of our knowledge, continuous subcutaneous infusion using osmotic pumps was successfully utilized for delivery of an antimicrobial peptide for the first time. Additionally, the potential of apidaecin analogs as novel antibiotics is demonstrated even in a scenario where the infection site is clearly separated from the route of administration.
Project description:Proline-rich antimicrobial peptides (PrAMPs) kill bacteria via a nonlytic mechanism in which they permeate through the outer membrane, utilize protein-mediated transport across the inner membrane, and target the ribosome to inhibit protein synthesis. We previously reported that substitutions of oncocin ( VDKPPYLPRPRPPRRIYNR-NH2 ) with a pair of cationic residues improved the antimicrobial activity. In this study, we applied the design protocol to three other PrAMPs: apidaecin-1b, pyrrhocoricin, and bactenecin 7(1-16) and found that the substitutions (R4K and I8K/R) for apidaecin-1b improve the activity by twofold (p?<?.05) against nonpathogenic Escherichia coli. Moreover, the substitutions (L7K/R and R14K) for pyrrhocoricin improve the activity by 2-10-fold (p?<?.05) against some strains of E. coli and Salmonella Typhimurium. We also performed activity tests against inner membrane protein (SbmA or YgdD) knockout strains. The result is consistent with previous studies that SbmA is the major transporter for apidaecin-1b and pyrrhocoricin derivatives. However, bactenecin 7(1-16) functions independently of these transporters. In addition, several apidaecin-1b derivatives exhibit enhanced activity relative to wild-type only in the absence of SbmA, which is consistent with mutations that enhance transport across the inner membrane. A high performance liquid chromatography-based kinetic assay for cellular association and internalization demonstrates that the selected cationic mutations can improve cellular association in minimal media, but this enhanced association is not required for increased activity, which suggests the importance of inner membrane transport. These functional studies on cationic mutants of PrAMPs advance understanding of potency and mechanism and advance the ability to engineer improved antimicrobials as evidenced by the identification of the pyrrhocoricin mutant (L7R and R14K) with 10-fold elevated potency against pathogenic E. coli.
Project description:Biochemical studies suggested that the antimicrobial peptide apidaecin (Api) inhibits protein synthesis by binding in the nascent peptide exit tunnel and trapping the release factor associated with a terminating ribosome. The mode of Api action in bacterial cells had remained unknown. Here genome-wide analysis reveals that in bacteria, Api arrests translating ribosomes at stop codons and causes pronounced queuing of the trailing ribosomes. By sequestering the available release factors, Api promotes pervasive stop codon bypass, leading to the expression of proteins with C-terminal extensions. Api-mediated translation arrest leads to the futile activation of the ribosome rescue systems. Understanding the unique mechanism of Api action in living cells may facilitate the development of new medicines and research tools for genome exploration.
Project description:Proline-rich antimicrobial peptides (PrAMPs) from insects and mammals have recently been evaluated for their pharmaceutical potential in treating systemic bacterial infections. Besides the native peptides, several shortened, modified, or even artificial sequences were highly effective in different murine infection models. Most recently, we showed that the 18-residue-long peptide Api88, an optimized version of apidaecin 1b, was efficient in two different animal infection models using the pathogenic Escherichia coli strains ATCC 25922 and Neumann, with a promising safety margin. Here, we show that Api88 is degraded relatively fast upon incubation with mouse serum, by cleavage of the C-terminal leucine residue. To improve its in vitro characteristics, we aimed to improve its serum stability. Replacing the C-terminal amide by the free acid or substituting Arg-17 with l-ornithine or l-homoarginine increased the serum stabilities by more than 20-fold (half-life, ?4 to 6 h). These analogs were nontoxic to human embryonic kidney (HEK 293), human hepatoma (HepG2), SH-SY5Y, and HeLa cells and nonhemolytic to human erythrocytes. The binding constants of all three analogs with the chaperone DnaK, which is proposed as the bacterial target of PrAMPs, were very similar to that of Api88. Of all the analogs tested, Api137 (Gu-ONNRPVYIPRPRPPHPRL; Gu is N,N,N',N'-tetramethylguanidino) appeared most promising due to its high antibacterial activity, which was very similar to Api88. Positional alanine and d-amino acid scans of Api137 indicated that substitutions of residues 1 to 13 had only minor effects on the activity against an E. coli strain, whereas substitutions of residues 14 to 18 decreased the activity dramatically. Based on the significantly improved resistance to proteolysis, Api137 appears to be a very promising lead compound that should be even more efficient in vivo than Api88.
Project description:Background:Antibiotic growth promoters (AGPs) have been used as growth promoters to maintain animal intestinal health and improve feed efficiency in broilers by inhibiting pathogen proliferation. In view of the growing emergence of antibiotic-resistant pathogen strains and drug residue issues, novel treatments are increasingly required. This study aimed to compare two antimicrobial approaches for managing pathogen infection and maintaining animal intestinal health in broilers by supplying Apidaecin Api-PR19 and AGPs over 42?d of a feeding trial. Results:Compared with the broilers that were only fed a corn-soybean basal diet (CON group), supplementation with Api-PR19 and AGP (respectively named the ABP and AGP groups) both increased the feed conversion efficiency. When compared with the AGP group, Api-PR19 supplementation could significantly increase the organ index of the bursa of fabricius and subtype H9 antibody level in broiler chickens. Moreover, when compared with the CON group, the intestinal villus height, intestinal nutrient transport, and intestinal sIgA content were all increased in the Api-PR19 group, while AGP supplementation was harmful to the intestinal villus height and intestinal nutrient transport. By assessing the antibacterial effect of Api-PR19 and antibiotics in vitro and in vivo, we found that Api-PR19 and antibiotics both inhibited the growth of pathogens, including Escherichia coli and Campylobacter jejuni. Furthermore, by using 16S rRNA gene sequencing, the beneficial bacteria and microbiota in broilers were not disturbed but improved by apidaecin Api-PR19, including the genera of Eubacterium and Christensenella and the species of uncultured_Eubacterium_sp, Clostridium_asparagiforme, and uncultured_Christensenella_sp, which were positively related to improved intestinal development, absorption, and immune function. Conclusion:Apidaecin Api-PR19 treatment could combat pathogen infection and had little negative impact on beneficial bacteria in the gut compared to antibiotic treatment, subsequently improving intestinal development, absorption, and immune function.