A Computational Guide for Choosing the Best Cell-Penetrating Peptides to Deliver Therapeutic Proteins Inside Cells | Research

The takeaway

A systematic bioinformatics pipeline screened 1,155 cell-penetrating peptides and identified 17 optimal candidates for delivering a therapeutic enzyme into cells, with N-terminal attachment working best.

1,155 → 17 CPPs
systematic computational screening narrowed over a thousand cell-penetrating peptides to 17 optimal candidates for protein delivery

What the researchers found

Researchers developed a systematic bioinformatics workflow for selecting optimal cell-penetrating peptides (CPPs) for covalent conjugation to therapeutic proteins. From 1,155 CPPs, 70 with the highest predicted uptake efficiency were screened. N-terminal conjugation produced significantly higher-quality constructs than C-terminal conjugation (p<0.05). Seventeen CPP conjugates were identified as the most promising based on translational efficacy, thermodynamic stability, aggregation risk, folding rate, flexibility, and protease susceptibility.

Why it matters

Getting therapeutic proteins inside cells is one of the biggest challenges in drug delivery. Cell-penetrating peptides can solve this but choosing the wrong CPP can damage the protein's structure and function. This systematic computational guide eliminates trial-and-error, making it faster and cheaper to design effective CPP-protein therapeutics.

The numbers in context

1,155 CPPs screened · 70 top candidates selected · 17 final promising constructs · N-terminal > C-terminal conjugation (p<0.05)

How the study worked

Computational bioinformatics workflow: 70 CPPs with the highest predicted uptake efficiency were selected from a database of 1,155. Each was computationally conjugated to the N- or C-terminus of CPG2 (glucarpidase). Constructs were evaluated for translational efficacy, thermodynamic properties, aggregation probability, folding rate, backbone flexibility, and protease susceptibility. N- vs C-terminal position effects were compared using unpaired t-tests.

Who was studied

Computational analysis of 1,155 cell-penetrating peptides and their conjugates with CPG2 enzyme

What this study cannot tell us

Entirely computational — no experimental validation of the predicted CPP-protein conjugates was performed. The workflow was demonstrated on a single model protein (CPG2), so generalizability to other cargo proteins is assumed but not proven. Computational predictions of uptake efficiency and stability may not perfectly reflect real-world behavior.

How to read the evidence

This is a computational bioinformatics study that provides a rational design framework without experimental validation. While the methodology is systematic and reproducible, the predicted constructs need experimental testing to confirm their real-world performance.

When this study was published

Published in 2019, this workflow remains relevant as computational peptide design tools continue to advance. The approach could now be enhanced with machine learning methods that have emerged since publication.

The bigger picture

Intracellular protein delivery is a holy grail in drug development. Many diseases (cancers, genetic disorders) have intracellular targets that current drugs can't reach. CPPs bridge this gap, and having a computational pipeline to rationally design CPP-protein conjugates could accelerate development of an entire class of new therapeutics — from enzymes to gene-editing proteins — that need to work inside cells.

Questions still open

Would the top 17 CPP-CPG2 constructs actually penetrate cells effectively when tested experimentally?
Can this workflow be automated into a web tool that any researcher could use for their protein of interest?
How well do the computational predictions correlate with actual cell-penetration efficiency in live cells?

Common questions

What are cell-penetrating peptides and why are they needed?

Cell-penetrating peptides (CPPs) are short peptides (typically 5-30 amino acids) that can cross cell membranes, carrying attached cargo like proteins or drugs inside cells. They're needed because most therapeutic proteins are too large and charged to enter cells on their own, yet many disease targets are located inside cells where these proteins need to act.

Why does it matter whether the peptide is attached to the front or back of the protein?

Attaching a CPP to different ends of a protein can affect how the protein folds, whether it remains functional, and how efficiently the CPP can pull it through the membrane. This study found that N-terminal (front) attachment consistently produced better constructs — more stable, better folded, and less likely to aggregate — providing a general design rule for CPP-protein conjugates.

Read the original research

Considerations on the Rational Design of Covalently Conjugated Cell-Penetrating Peptides (CPPs) for Intracellular Delivery of Proteins: A Guide to CPP Selection Using Glucarpidase as the Model Cargo Molecule.

Molecules (Basel, Switzerland), 24(23)

View on PubMed ↗Publisher’s paper ↗

Citation

Behzadipour, Yasaman; Hemmati, Shiva. (2019). Considerations on the Rational Design of Covalently Conjugated Cell-Penetrating Peptides (CPPs) for Intracellular Delivery of Proteins: A Guide to CPP Selection Using Glucarpidase as the Model Cargo Molecule.. Molecules (Basel, Switzerland), 24(23). https://doi.org/10.3390/molecules24234318