Breaking the Chain of Resistance: LL-37_Renalexin, a New Antimicrobial Peptide Against Superbugs


The rapid evolution of antibiotic resistance in bacteria like Enterococcus faecium, Staphylococcus aureus, and Klebsiella pneumoniae, among others, has rendered many standard treatments ineffective. These pathogens have developed intrinsic and extrinsic mechanisms to resist traditional antibiotics such as gentamycin, ciprofloxacin, and ampicillin. The failure of these drugs leads to complications in treating infections, posing a significant threat to public health. Antimicrobial peptides (AMP) have recently been recognized as potential alternatives to traditional antibiotics due to their unique modes of action. These peptides are usually cationic and amphipathic, comprising 10-100 amino acid residues. They exert their antimicrobial effects by disrupting bacterial cell walls and membranes or inhibiting DNA replication and protein synthesis. AMPs like defensins, LL-37, gramicidins D, and Renalexin have shown efficacy against resistant bacterial strains.

A new study published in the Journal Applied Microbiology and Biotechnology by Julius Kwesi Narh, Professor Nestor Casillas-Vega and led by Professor Xristo Zarate from the Autonomous University of Nuevo Leon in Mexico, designed a novel hybrid AMP named LL-37_Renalexin, which demonstrated potent antibacterial properties against various clinically relevant pathogens. The researchers used advanced bioengineering techniques to combine two known AMPs, LL-37 and Renalexin, using a GS peptide linker. This innovative design aimed to harness the strengths of both peptides in one potent compound. They expressed the new hybrid peptide using carrier proteins SmbP and CusF3H+. These proteins were used to enhance the stability and expression levels of LL-37_Renalexin in bacterial systems. The team employed Escherichia coli strains BL21(DE3) and SHuffle T7(DE3) as hosts for peptide expression. These strains are known for their efficiency in protein production. They used immobilized metal affinity chromatography for the purification of LL-37_Renalexin, ensuring high purity and yield.

The researchers synthesized DNA encoding the hybrid peptide and cloned it into expression vectors for production in E. coli. They conducted small-scale expressions to verify the presence of the peptide in the soluble cell lysate, followed by large-scale expression to produce sufficient quantities for testing. The fusion proteins were purified using chromatography techniques, ensuring that the peptide was isolated in its pure form. To obtain the tag-free peptide, they utilized enterokinase to cleave off the carrier proteins from the hybrid peptide.

The team tested the antimicrobial efficacy of LL-37_Renalexin against various bacterial strains, including S. aureus, E. coli, MRSA, and K. pneumoniae. The authors demonstrated that LL-37_Renalexin has a significant reduction in bacterial colony-forming units, showcasing its effectiveness against multiple bacterial strains. The hybrid peptide required lower concentrations to inhibit bacterial growth compared to its individual components, suggesting greater potency. LL-37_Renalexin exhibited a broad spectrum of activity against both Gram-positive and Gram-negative bacteria. The hybrid peptide’s mechanism involves disruption of the bacterial membrane, pore formation, and possible inhibition of vital cellular processes. The study emphasizes the multifunctional nature of LL-37_Renalexin, highlighting its ability to target various bacterial strains effectively. One key advantage of the design is the GS linker and carrier proteins which contributed to the stable and soluble expression of the hybrid peptide. Another advantage is  safety where LL-37_Renalexin did not exhibit toxicity to human cells, indicating its potential for safe therapeutic use.

According to the authors, the newly developed hybrid peptide offers several advantages. Firstly, it addresses the urgent need for new antimicrobial agents in the face of rising antibiotic resistance. Secondly, its method of production via recombinant DNA technology makes it a viable option for large-scale production. Lastly, the peptide’s efficacy at lower concentrations could reduce potential side effects, making it a safer therapeutic option. In conclusion, the findings of Professor Xristo Zarate and colleagues are significant in the field of antimicrobial research and offer a promising avenue for developing new treatments for antibiotic-resistant infections. This research could pave the way for more effective, safe, and targeted antimicrobial therapies. Professor Xristo Zarate  said “We’ve created a new superbug-fighting weapon: LL-37_Renalexin, a hybrid antimicrobial peptide that’s like a one-two punch for drug-resistant bacteria. It’s got the power of two existing AMPs, LL-37 and Renalexin, combined into one potent package. And the best part? It works at lower doses than either of its parent peptides, meaning less chance of side effects. This is a game-changer for the fight against antibiotic resistance”.

Breaking the Chain of Resistance: LL-37_Renalexin, a New Antimicrobial Peptide Against Superbugs - Medicine Innovates
Figure: Recombinant hybrid antimicrobial peptide LL-37_Renalexin-mediated antibacterial extracellular and intracellular actions.

About the author

Néstor G. Casillas Vega, Ph. D.
Professor and Researcher in Medical Microbiology

  • Professor and Principal Investigator at the Universidad Autónoma de Nuevo León, Mexico.
  • Master and Doctor of Science with orientation in Medical Microbiology.
  • Leader of the academic body “Laboratory of Clinical Pathology” (UANL-CA-447), Secretary of Public Education (SEP).
  • CEO and founder of GEMMBIOMA – Molecular Diagnostic Laboratory.
  • Member of:
    • National System of Researchers Level II of the Consejo Nacional de Humanidades Ciencias y Tecnologías, CONAHCYT.
    • Academic Committee of the General Exam for the graduation of the degree of Clinical Chemistry, Centro Nacional de Evaluación para la Educación Superior, CENEVAL.
    • Mexican Association of Infectology and Clinical Microbiology, A.C.
    • European Society of Clinical Microbiology and Infectious Diseases.
    • International Union Against Sexually Transmitted Infections.
  • Participation as a professor at the Faculty of Medicine of the University of Monterrey, UDEM.
  • Recognition Desirable Profile PROMEP of the Ministry of Public Education.
  • Certification by the Centers for Disease Control and Prevention (CDC), World Health Organization (WHO), and Pan American Health Organization (PAHO).
  • Research stays in Virology at the Universidad Autónoma de Madrid, Spain.
  • Diplomas in tutor training and university teaching.
  • Editor of national and international scientific journals of high prestige.
  • Author of books, manuals, and multiple scientific articles in indexed journals.
  • A jury of evaluation in postgraduate exams in different faculties.
  • Training of human resources: doctorate, master’s degree, specialty, and bachelor’s degree.
  • Principal investigator of multiple research papers on microbiology, molecular epidemiology of sexually transmitted infections, gastrointestinal infections, and clinical laboratory.
  • Evaluator of CONAHCYT (Frontier Science, postgraduate scholarships abroad – Doctorates in Sciences and Humanities).
  • More than 100 conferences and papers in microbiology were presented at national and international congresses.




About the author

Julius Kwesi Narh      


As a self-motivated and first-generation scientist at the early stage of my scientific research career, I am interested in the molecular and cellular mechanisms underlying bacterial pathogenesis, bacterial genomics, mRNA stability, and resistance under antibacterial and reactive oxygen and chlorine species (RO/CS) stress conditions. Additionally, I am keenly interested in the design, production, and purification of novel therapeutic peptide-based (AMPs) drugs against infection and cancer.

I just completed a two-year Master of Science (MRes) degree in Applied Microbiology from the Autonomous University of Nuevo Leon, Mexico (2023), where my research delves into the areas of antimicrobial peptide design, recombinant therapeutic peptide production and purification, and its bioassays (Dr. Xristo’s Laboratory) yielding a scientific manuscript accepted for publication in the Journal of Applied Microbiology and Biotechnology, Springer.

I hold a Bachelor of Science degree in Biotechnology and Molecular Biology (First Class) from the University for Development Studies, Ghana (2019), where my research delves into the areas of molecular parasitology (Dr. Addy’s Laboratory) yielding two research publications as a co-author.

Currently, I enjoy playing with immunoinformatic tools for the design and development of peptide-based microbial vaccines and diagnostics kits for the detection of infectious agents and cancer biomarkers.

About the author

Xristo Zarate Kalfopulos, Ph.D

Dr. Xristo stands as an esteemed Associate Professor and the Graduate Program Coordinator in the Department of Applied Microbiology within the School of Chemical Sciences (FCQ) at the Autonomous University of Nuevo Leon (UANL) in Mexico. As the lead and Principal Investigator (PI) at the Protein Expression and Purification Laboratory, Dr. Xristo has garnered recognition for his notable contributions to the realm of recombinant protein production and purification, along with expertise in cell-free expression systems.

Renowned for his achievements, Prof. Xristo boasts an array of research publications and patented innovations. Among his notable accomplishments, he has conceived and developed two innovative protein tags, enabling efficient cytosolic and periplasmic expression of recombinant proteins and peptides with antibacterial and anticancer properties. Furthermore, he has mastered the purification of these proteins using state-of-the-art immobilized metal affinity chromatography techniques.

Prof. Xristo’s research group has not only amassed numerous research grants but has also been honored with awards over the years, solidifying their position at the pinnacle of advanced research within the University. Dr. Xristo’s laboratory is equipped with cutting-edge technology, fostering a conducive environment for rigorous research. Here, he dedicates himself to mentoring and training both Master’s (MSc.) and Doctorate (Ph.D.) students enrolled in the Applied Microbiology and Pharmacy programs, shaping the future leaders in these fields.

Laboratory website


Julius Kwesi Narh, Nestor G Casillas-Vega and Xristo Zarate. LL-37_Renalexin hybrid peptide exhibits antimicrobial activity at lower MICs than its counterpart single peptides. Applied Microbiology and Biotechnology 108, 126 (2024)