WRAP peptide is a 15-amino acid-long transfecting agent that can WRAP'n ROLL around nucleic acids to form nanoparticles. Those nanoparticles can easily penetrate the cells and deliver their precious cargoes such as plasmids or siRNA
A few years ago... How I met WRAP (and its publication)
When I was an intern within the public/private joint unit Sys2Diag I met with Gudrun, a peptide chemist with plenty of promising peptide based projects. Among them were the WRAP peptide series : short peptides (less than 16 amino acids, mostly made of leucine, tryptophan and arginine residues) with an impressive potential as transfection reagent.
Peptide-Based Nanoparticles to Rapidly and Efficiently “Wrap ’n Roll” siRNA into Cells Bioconjugate Chem. 2019, 30, 592−603
For a quick overview, allow me now to introduce you to those tiny peptidic vectors!
First, why are transfection peptides important?
When I study a research tool I am always wondering: what challenge is awaking these scientists every morning? What unmet need drives them to innovate?
In the case of WRAPs, the challenge is: breaking into the cell unnoticed!
Entering the cell and delivering a cargo is a central aspect in plenty of biotechnologies, say for example: RNA intefererence, Plasmid Transfection, Crisp-Cas9 gene editing, the COVID-19 vaccine (!). A few techniques exist to achieve that (see on the left).
Ideally, you want your entry method to be cheap, efficient while also being minimally disruptive for the cells. Easier said than done...
Calcium phospate and electroporation are simple methods, yet can only be applied in vitro. Lipofectamine and viral methods are compatible with in vivo models but are trickier to produce and handle.
Being composed of natural amino-acids, peptidic transfecting agents are : i) stable in solution ii) able to transfect many cell types with nearly no toxicity iii) open for chemical modification to increase specificity or stability in vivo .
All this added-up makes them very interesting vector molecules.
How do they work?
WRAP peptides work in a 3-step process: 1. Assembly into nanoparticles; 2. Internalization and 3. Delivery of the siRNA/plasmid
1. Nanoparticle Assembly
Thanks to their structure and amino acid composition, WRAP peptides bind the nucleic acids in a non-covalent fashion. They self-assemble into small nanoparticles (100 nm) which can be observed using Transmission Electron Microscopy (TEM).
When added to cells, the nanoparticles enter the cell by direct translocation. This process is spontaneous due to the positive charges of the nanoparticle surface.
The internalization can be visualized using epifluorescence microscopy. Here, a fluorescent siRNA (red) highlights the internalization of the nanoparticle within the cell (nucleus in blue)
3. Gene Knock Down with siRNA
Once inside the cell, the siRNA is released and could quickly silence the targeted gene expression as seen in the graphs on the right. 20nM siRNA targeting the CDK4 protein loaded in WRAP nanoparticles were incubated (5 min to 60 min) and CDK4 expression was recorded showing a net decrease in protein expression even after only 5 min incubation.