Study on activation mechanism and cleavage sites of recombinant butelase-1 zymogen derived from Clitoria ternatea

An efficient and easily obtainable butelase variant for chemoenzymatic ligation and modification of peptides and proteins

The expanding field of site-specific ligation of proteins and peptides has catalyzed the development of novel methods that enhance molecular modification. Among these methods, enzymatic strategies have emerged as dominant due to their specificity and efficiency in modifying proteins under mild conditions. Asparaginyl endopeptidase is a group of cyclotide-producing cysteine proteases from plants. These plant cysteine proteases, known for their specificity, effectively recognize the tripeptide motif (Asx-Xaa-Yaa) and cleave at the C-terminal side of Asx residues, forming acyl-enzyme intermediates that facilitate transpeptidation. Butelase 1 stands out as the most efficient AEP for protein engineering, yet challenges in its expression and purification limit its accessibility for widespread research and industrial use. To address these challenges, we engineered a new, catalytically efficient variant of Butelase 1, Butelase AY, by mutating the gatekeeping residues Val237Ala and Thr238Tyr within the LAD-1 region. These modifications significantly enhanced the stability and yield of Butelase AY, allowing for successful application in various peptide and protein engineering tasks. Butelase AY was tested on the peptide GLGKY, the globular protein GFP, and the intrinsically disordered protein α-synuclein, effectively labeling them with a fluorescent probe. Notably, Butelase AY maintained its efficiency with substrates containing unnatural amino acids, making it a promising candidate for biorthogonal applications. Importantly, the mutations did not compromise the enzyme's specificity, as it continued to process model peptides and native protein substrates with N-term NHV recognition motifs effectively. In conclusion, Butelase AY presents a novel recombinant tool for diverse protein labeling and modifications, particularly in biorthogonal strategies. This innovation has the potential to expand applications in biotechnology and therapeutic development, ultimately revolutionizing protein engineering and its utility in synthetic biology.

Total Biosynthesis of Circular Bacteriocins by Merging the Genetic Engineering and Enzymatic Catalysis

Circular bacteriocins are known for their structural stability and effective antimicrobial properties, positioning them as potential natural food preservatives. However, their widespread application is impeded by restricted availability. This research developed a total biosynthesis platform for circular bacteriocins, with a focus on AS-48 by involving recombinant production of the linear precursor in Escherichia coli, followed by enzymatic cyclization of the precursor into cyclic AS-48 using the ligase butelase-1 in vitro. An important discovery is that, aside from fusion tags, the C-terminal motif LE and LEKKK also could affect the expression yield of the precursor. This biosynthesis platform is both versatile and high-yielding, achieving yields of 10-20 mg/L of AS-48. Importantly, the biosynthetic AS-48 exhibited a secondary structure and antimicrobial activities comparable to those of the native molecules. As such, this work proposes an effective synthetic approach for circular bacteriocins, facilitating their advancement and application in the food industry.

"Top-down" overexpression optimization of butelase-1 in Escherichia coli and its application in anti-tumor peptides

Butelase-1, the fastest known Asn/Asp-specific peptide ligase capable of catalyzing peptide ligation and cyclization, holds promising application prospects in the fields of food and biology. However, limited research exists on its recombinant expression and potential applications in peptide drugs. In this study, the activity of recombinantly-produced butelase-1 was enhanced by co-expressing it with a molecular chaperone in the SHuffle T7 strain. By introducing single or multiple synonymous rare codons at the beginning of the coding regions of beta-strand or alpha-helix, in combination with ribosomal binding site engineering, the activity of butelase-1 could be further improved. Consequently, the butelase-1 with a specific activity of 386.93 U/mg and a catalytic efficiency of 11,048 M-1 s-1 was successfully prepared in E. coli, resulting in a total activity of 8183.54 U/L and a yield of about 100 mg/L. This optimized butelase-1 was then used to efficiently cyclize the redesigned anti-cancer peptide lunasin, leading to enhanced bioavailability and anti-cancer effects. Overall, this study not only provided valuable biotechnology strategies for improving the recombinant expression of butelase-1 but also demonstrated a successful application for enhancing the biological efficacy of anti-cancer peptides.

Consensus design and engineering of an efficient and high-yield peptide asparaginyl ligase for protein cyclization and ligation

Plant legumains are Asn/Asp-specific endopeptidases that have diverse functions in plants. Peptide asparaginyl ligases (PALs) are a special legumain subtype that primarily catalyze peptide bond formation rather than hydrolysis. PALs are versatile protein engineering tools but are rarely found in nature. To overcome this limitation, here we describe a two-step method to design and engineer a high-yield and efficient recombinant PAL based on commonly found asparaginyl endopeptidases. We first constructed a consensus sequence derived from 1500 plant legumains to design the evolutionarily stable legumain conLEG that could be produced in E. coli with 20-fold higher yield relative to that for natural legumains. We then applied the ligase-activity determinant hypothesis to exploit conserved residues in PAL substrate-binding pockets and convert conLEG into conPAL1-3. Functional studies showed that conLEG is primarily a hydrolase, whereas conPALs are ligases. Importantly, conPAL3 is a superefficient and broadly active PAL for protein cyclization and ligation.

Butelase 1-Mediated Enzymatic Cyclization of Antimicrobial Peptides: Improvements on Stability and Bioactivity

Antimicrobial peptides (AMPs) have broad-spectrum antibacterial properties and safety as food preservatives, whereas the stability and antibacterial activity require improvement. Here, the "head-to-tail" cyclization of linear AMP GKE was catalyzed by butelase 1, which resulted in an improved pronouncedly antibacterial effect. Cell morphology and propidium iodide uptake revealed that the increased membrane permeability was one of the bacteriostatic mechanisms of GKE and could be enhanced after cyclization. As cyclic GKE (cGKE) exhibited more stability than the linear counterpart under the microorganism culture environment, the increase in effective bacteriostatic concentration should be a reason for the superior antibacterial effect. Moreover, cGKE exhibited the ordered secondary structure, while GKE possessed a similar structure only in sodium dodecyl sulfate micelles. The structure was also beneficial to improve the antibacterial activity caused by the increased affinity of cGKE to the membranes. Overall, butelase 1-mediated cyclization is a promising strategy for enhancing the antibacterial activity of linear AMPs.