Expression and purification of lacticin Q by small ubiquitin-related modifier fusion in Escherichia coli

Functional expression of diverse post-translational peptide-modifying enzymes in Escherichia coli under uniform expression and purification conditions

RiPPs (ribosomally-synthesized and post-translationally modified peptides) are a class of pharmaceutically-relevant natural products expressed as precursor peptides before being enzymatically processed into their final functional forms. Bioinformatic methods have illuminated hundreds of thousands of RiPP enzymes in sequence databases and the number of characterized chemical modifications is growing rapidly; however, it remains difficult to functionally express them in a heterologous host. One challenge is peptide stability, which we addressed by designing a RiPP stabilization tag (RST) based on a small ubiquitin-like modifier (SUMO) domain that can be fused to the N- or C-terminus of the precursor peptide and proteolytically removed after modification. This is demonstrated to stabilize expression of eight RiPPs representative of diverse phyla. Further, using Escherichia coli for heterologous expression, we identify a common set of media and growth conditions where 24 modifying enzymes, representative of diverse chemistries, are functional. The high success rate and broad applicability of this system facilitates: (i) RiPP discovery through high-throughput “mining” and (ii) artificial combination of enzymes from different pathways to create a desired peptide.

Design and in silico analysis of a whole-cell biosensor able to kill methicillin-resistant Staphylococcus aureus

The rise of methicillin-resistant Staphylococcus aureus (MRSA) infections has gained concern throughout the world over the past decades. Alternative therapeutic agents to antibiotics are rapidly growing to impede the proliferation of MRSA-caused infections. Lately, synthetic biology techniques have developed whole-cell biosensors by designing gene circuitry capable of sensing quorum-sensing (QS) molecules of pathogens and triggering expression of an antimicrobial moiety that kills MRSA and therefore prevents its further proliferation. Here, an E. coli was engineered in silico to act as a whole-cell biosensor that senses QS molecules from MRSA and triggers the expression of a bacteriocin that kills MRSA. To achieve this functionality, biosensor and bacteriocin modules were constructed and assembled into a vector. Both modules were codon-optimized to increase the yield production of the recombinant proteins. We then demonstrate in silico that the construction of a dual biosensor-killer plasmid, which holds two genetical modules known as biosensor and bacteriocin modules, enables the recombinant host to sense QS molecules from MRSA. Our designed whole-cell biosensor demonstrates in silico its ability to produce and secrete the bacteriocin as a function of the external concentration of autoinducer peptide from MRSA. These in silico results unravel the possibility of designing antimicrobial smarter therapeutics against resistant pathogens.

Mining, heterologous expression, purification, antibactericidal mechanism, and application of bacteriocins: A review

Bacteriocins are generally considered as low-molecular-weight ribosomal peptides or proteins synthesized by G⁺ and G^- bacteria that inhibit or kill other related or unrelated microorganisms. However, low yield is an important factor restricting the application of bacteriocins. This paper reviews mining methods, heterologous expression in different systems, the purification technologies applied to bacteriocins, and identification methods, as well as the antibacterial mechanism and applications in three different food systems. Bioinformatics improves the efficiency of bacteriocins mining. Bacteriocins can be heterologously expressed in different expression systems (e.g., Escherichia coli, Lactobacillus, and yeast). Ammonium sulfate precipitation, dialysis membrane, pH-mediated cell adsorption/desorption, solvent extraction, macroporous resin column, and chromatography are always used as purification methods for bacteriocins. The bacteriocins are identified through electrophoresis and mass spectrum. Cell envelope (e.g., cell permeabilization and pore formation) and inhibition of gene expression are common antibacterial mechanisms of bacteriocins. Bacteriocins can be added to protect meat products (e.g., beef and sausages), dairy products (e.g., cheese, milk, and yogurt), and vegetables and fruits (e.g., salad, apple juice, and soybean sprouts). The future research directions are also prospected.

Fighting biofilms with lantibiotics and other groups of bacteriocins

Biofilms are sessile communities of bacteria typically embedded in an extracellular polymeric matrix. Bacterial cells embedded in biofilms are inherently recalcitrant to antimicrobials, compared to cells existing in a planktonic state, and are notoriously difficult to eradicate once formed. Avenues to tackle biofilms thus far have largely focussed on attempting to disrupt the initial stages of biofilm formation, including adhesion and maturation of the biofilm. Such an approach is advantageous as the concentrations required to inhibit formation of biofilms are generally much lower than removing a fully established biofilm. The crisis of antibiotic resistance in clinical settings worldwide has been further exacerbated by the ability of certain pathogenic bacteria to form biofilms. Perhaps the most notorious biofilm formers described from a clinical viewpoint have been methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis, Pseudomonas aeruginosa, Gardnerella vaginalis and Streptococcus mutans, the latter of which is found in oral biofilms. Due to the dearth of novel antibiotics in recent decades, compounded by the increasing rate of emergence of resistance amongst pathogens with a propensity for biofilm formation, solutions are urgently required to mitigate these crises. Bacteriocins are a class of antimicrobial peptides, which are ribosomally synthesised and often are more potent than their antibiotic counterparts. Here, we review a selection of studies conducted with bacteriocins with the ultimate objective of inhibiting biofilms. Overall, a deeper understanding of the precise means by which a biofilm forms on a substrate as well as insights into the mechanisms by which bacteriocins inhibit biofilms is warranted.

Design, characterization and expression of a novel hybrid peptides melittin (1-13)-LL37 (17-30)

Hybridizing of different antimicrobial peptides (AMPs) has been a common practice for obtaining novel hybrid AMPs with elevated antibacterial activity but minimized cytotoxicity. The hybrid peptides melittin (1-13)-LL37 (17-30) (M-L) combining the hydrophobic N-terminal fragment of melittin (M) with the core antibacterial fragment of LL37 (L), was designed for the first time to explore its antibacterial activity and hemolytic activity against bacteria and sheep erythrocyte respectively. Results showed that M-L had an even more potent antibacterial activity against all indicator strains (especially gram-positive bacteria) than M and L, whereas didn't exhibit hemolytic activity to sheep erythrocytes, implying M-L can be served as a potential therapeutic drug to substitute traditional antibiotics. However the high expense of biosynthesis limited its further research, therefore fusion expression of M-L was carried out in Escherichia coli (E. coli) for overproducing the hybrid peptide so as to solve the problem. The DNA sequence encoding M-L with preferred codons was cloned into the pET-SUMO vector for protein expression in E. coli BL21 (DE3). After IPTG induction, approximately 165 mg soluble fusion protein SUMO-M-L was recovered per liter supernatant of the fermentation ultrasonic lysate using Ni-NTA Sepharose column (92 % purity). And 23 mg recombinant M-L was obtained per liter culture after cleavage of SUMO protease and purification of Ni-NTA Sepharose column. In sum, this research not only supplied an effective approach for overproducing hybrid peptide M-L, but paved the way for its further exploration on pharmaceutical potential and medical importance.

Secretory expression of lacticin Q fused with SUMO in Bacillus subtilis

Lacticin Q is a 53-amino acid Class II bacteriocin produced by Lactococcus lactis QU 5. It shows antibacterial activity comparable to that of nisin A in terms of both spectrum and intensity. Moreover, it remains stable at alkaline pH values, while nisin A was inactivated. It may possibly be employed as an alternative to or in combination with nisin A. The objective of this study was to express lacticin Q extracellularly with Small ubiquitin-related modifier (SUMO) fusion technology in Bacillus subtilis. Secretory SUMO-lacticin Q fusion protein was efficiently produced in B. subtilis WB600 transformed with the recombinant expression plasmid and accounted for 19% of the culture supernatant proteins. Fusion SUMO-lacticin Q was purified by nickel nitrilotriacetate (Ni-NTA) affinity chromatography and digested with SUMO protease to release lacticin Q. Lacticin Q was further purified by Ni-NTA chromatography to yield about 2.5 mg of lacticin Q with more than 93% purity from 1L of supernatant of fermentation culture. An activity assay indicated that the recombinant bacteriocin exhibited excellent antimicrobial activity against indicator strains. The results obtained suggest that the secretory lacticin Q was efficiently expressed using SUMO fusion technology in B. subtilis. The expression and purification system could promote the application of lacticin Q in food and medicine.