Unique C-terminal extension and interactome of Mycobacterium tuberculosis GlmU impacts it's in vivo function and the survival of pathogen

N-acetyl glucosamine-1-phosphate uridyltransferase (GlmU) is a bifunctional enzyme involved in the biosynthesis of Uridine diphosphate N-acetylglucosamine (UDP-GlcNAc). UDP-GlcNAc is a critical precursor for the synthesis of peptidoglycan and other cell wall components. The absence of a homolog in eukaryotes makes GlmU an attractive target for therapeutic intervention. Mycobacterium tuberculosis GlmU (GlmUMt) has features, such as a C-terminal extension, that are not present in GlmUorthologs from other bacteria. Here, we set out to determine the uniqueness of GlmUMt by performing in vivo complementation experiments using RvΔglmU mutant. We find that any deletion of the carboxy-terminal extension region of GlmUMt abolishes its ability to complement the function of GlmUMt. Results show orthologs of GlmU, including its closest ortholog, from Mycobacterium smegmatis, cannot complement the function of GlmUMt. Furthermore, the co-expression of GlmUMt domain deletion mutants with either acetyl or uridyltransferase activities failed to rescue the function. However, co-expression of GlmUMt point mutants with either acetyl or uridyltransferase activities successfully restored the biological function of GlmUMt, likely due to the formation of heterotrimers. Based on the interactome experiments, we speculate that GlmUMt participates in unique interactions essential for its in vivo function.

Degrasyn exhibits antibiotic activity against multi-resistant Staphylococcus aureus by modifying several essential cysteines

Degrasyn inhibits deubiquitination enzymes and has anti-cancer activity. We here show that it also exhibits antimicrobial activity against multi-resistant Staphylococcus aureus. Structure activity relationship studies demonstrate an important role of the electrophilic α-cyanoacrylamide moiety as a Michael acceptor. A suite of chemical proteomic techniques unraveled binding of this moiety to various cysteine residues of essential proteins in a reversibly covalent manner.

Rapid and efficient production of cecropin A antibacterial peptide in Escherichia coli by fusion with a self-aggregating protein

BACKGROUND

Cecropin A (CeA), a natural cationic antimicrobial peptide, exerts potent antimicrobial activity against a broad spectrum of Gram-positive and Gram-negative bacteria, making it an attractive candidate substitute for antimicrobials. However, the low production rate and cumbersome, expensive processes required for both its recombinant and chemical synthesis have seriously hindered the exploitation and application of CeA. Here, we utilized a short β-structured self-aggregating protein, ELK16, as a fusion partner of CeA, which allowed the efficient production of high-purity CeA antibacterial peptide with a simple inexpensive process.

RESULTS

In this study, three different approaches to the production of CeA peptide were investigated: an affinity tag (His-tag)-fused protein expression system (AT-HIS system), a cell-free protein expression system (CF system), and a self-assembling peptide (ELK16)-fused protein expression system (SA-ELK16 system). In the AT-HIS and CF systems, the CeA peptide was obtained with purities of 92.1% and 90.4%, respectively, using one or more affinity-chromatographic purification steps. The procedures were tedious and costly, with CeA yields of only 0.41 and 0.93 μg/mg wet cell weight, respectively. Surprisingly, in the SA-ELK16 system, about 6.2 μg/mg wet cell weight of high-purity (approximately 99.8%) CeA peptide was obtained with a simple low-cost process including steps such as centrifugation and acetic acid treatment. An antimicrobial test showed that the high-purity CeA produced in this study had the same antimicrobial activity as synthetic CeA peptide.

CONCLUSIONS

In this study, we designed a suitable expression system (SA-ELK16 system) for the production of the antibacterial peptide CeA and compared it with two other protein expression systems. A high yield of high-purity CeA peptide was obtained with the SA-ELK16 system, which greatly reduced the cost and time required for downstream processing. This system may provide a platform for the laboratory scale production of the CeA antibacterial peptide.