CRAMP18-35 peptide conjugated to chitosan via click chemistry retained activity against Gram-negative bacteria but lost activity against Gram-positive species.
Selective Gram-negative activityConjugation to chitosan changed the peptide's spectrum from broad-spectrum to Gram-negative-only
What the researchers found
CRAMP18-35 (a fragment of mouse cathelicidin) was conjugated to chitosan and hydroxypropyl chitosan using copper-catalyzed azide-alkyne cycloaddition (CuAAC, a click chemistry reaction). The degree of substitution was 0.20 for chitosan and 0.13 for HPC conjugates.
The conjugates showed selective antibacterial activity against Gram-negative bacteria (E. coli and P. aeruginosa) and lacked activity against Gram-positive bacteria (S. aureus and E. faecalis). This selectivity was a notable finding because the free peptide is typically active against both types.
Why it matters
Antibiotic resistance is a global crisis. Gram-negative bacteria are especially hard to treat because of their double membrane. Combining antimicrobial peptides with chitosan could create wound dressings or coatings that kill resistant bacteria. Chitosan itself is biocompatible and biodegradable.
The numbers in context
- Peptide: CRAMP18-35 (mouse cathelicidin fragment)
- Degree of substitution: 0.20 (chitosan), 0.13 (HPC)
- Active against: E. coli, P. aeruginosa (Gram-negative)
- Inactive against: S. aureus, E. faecalis (Gram-positive)
- Conjugation method: CuAAC click chemistry
How the study worked
Chitosan azide and HPC-azide were prepared by reacting with imidazole sulfonyl azide hydrochloride. CRAMP18-35 with an N-terminal pentynoyl group was conjugated via CuAAC. Conjugates were characterized by IR spectroscopy and proton NMR. Antibacterial activity was tested against two Gram-positive and two Gram-negative bacterial species.
Who was studied
In vitro testing against four bacterial species: E. coli, P. aeruginosa, S. aureus, E. faecalis
What this study cannot tell us
The selectivity change (losing Gram-positive activity after conjugation) was not explained mechanistically. The conjugation may alter the peptide's ability to interact with Gram-positive cell walls. In vitro antibacterial testing does not predict in vivo wound healing efficacy. Copper catalyst residues from click chemistry could be a biocompatibility concern. No cytotoxicity testing was reported.
How to read the evidence
Rated preliminary: in vitro antibacterial testing showing proof of concept for the conjugation chemistry.
When this study was published
Published in 2024. Part of the growing field of peptide-polymer conjugates for antimicrobial applications.
The bigger picture
Antibiotic resistance is a global crisis, particularly for Gram-negative bacteria. Combining antimicrobial peptides with chitosan could create wound dressings or coatings that resist bacterial growth.
Questions still open
- Why did conjugation eliminate Gram-positive activity?
- Could different conjugation strategies preserve broader-spectrum activity?
Common questions
What are antimicrobial peptides?
Why combine peptides with chitosan?
Read the original research
Conjugation of CRAMP18-35 Peptide to Chitosan and Hydroxypropyl Chitosan via Copper-Catalyzed Azide-Alkyne Cycloaddition and Investigation of Antibacterial Activity.
International journal of molecular sciences, 25(17)
Citation
Rathinam, Sankar; Sørensen, Kasper K; Hjálmarsdóttir, Martha Á; Thygesen, Mikkel B; Másson, Már. (2024). Conjugation of CRAMP18-35 Peptide to Chitosan and Hydroxypropyl Chitosan via Copper-Catalyzed Azide-Alkyne Cycloaddition and Investigation of Antibacterial Activity.. International journal of molecular sciences, 25(17). https://doi.org/10.3390/ijms25179440