This review describes emerging methods — including cell-penetrating peptides — for delivering custom-built synthetic proteins into living cells to study biological processes that genetic tools alone cannot access.
Beyond the plasma barrierCell-penetrating peptides and other delivery methods now allow custom-built synthetic proteins to cross cell membranes and be studied in their natural biological environment for the first time.
What the researchers found
The review highlights two main delivery strategies compatible with synthetic proteins: cell-penetrating peptides (CPPs) and multiplexed bead loading (MBL). CPPs are short peptide sequences that can transport synthetic proteins across the cell membrane, while MBL uses physical methods to introduce proteins into cells.
These delivery methods enable the study of posttranslational modifications (PTMs) — chemical changes that happen to proteins after they are made — in living cells. This is significant because PTMs regulate critical cellular processes but cannot be precisely controlled through genetic manipulation alone. The authors demonstrate applications including tracking protein localization, degradation, folding, interactions, and involvement in liquid-liquid phase separation organelles.
Why it matters
Many diseases involve errors in how proteins are chemically modified after they are made. Understanding these modifications requires studying custom-built proteins inside living cells — something genetic tools cannot fully achieve. By advancing delivery methods, particularly using cell-penetrating peptides, this field opens new possibilities for understanding disease mechanisms and potentially developing targeted therapies.
How the study worked
This is a review article (Account) in which the authors survey recent developments in protein delivery methods, evaluate their compatibility with chemically synthesized proteins, and describe their own work using cell-penetrating peptides and multiplexed bead loading. The review compares strengths and weaknesses of different delivery approaches for both protein introduction and subsequent biological studies.
What this study cannot tell us
As a review article, this paper synthesizes existing work rather than presenting new experimental data. The delivery methods discussed still face challenges including limited efficiency, potential cytotoxicity, and difficulty achieving consistent delivery across different cell types. Many of the applications described are still in early research stages and have not been validated in therapeutic contexts.
How to read the evidence
This is a review article (Account) published in a high-impact chemistry journal, summarizing the state of the field rather than presenting new experimental results. It provides a comprehensive overview of methods and applications but should be interpreted as expert perspective rather than primary evidence.
When this study was published
Published in 2022, this review captures the state of protein delivery research up to that point. The field continues to evolve rapidly, with new delivery strategies and applications being developed regularly.
The bigger picture
Cell-penetrating peptides are themselves a major class of peptide therapeutics and research tools. This review sits at the intersection of peptide chemistry, protein engineering, and cell biology, illustrating how peptide-based tools can solve fundamental problems in studying cellular processes. The ability to deliver precisely engineered proteins into cells could transform drug development, disease research, and our understanding of basic biology.
Questions still open
- Can cell-penetrating peptide delivery be scaled efficiently enough for therapeutic protein delivery in patients?
- How do different delivery methods affect the biological activity of the synthetic proteins once inside cells?
- Could these approaches be combined with CRISPR and other genetic tools to create more comprehensive research platforms?
Common questions
What are cell-penetrating peptides and how do they deliver proteins into cells?
Why can't scientists just use genetic engineering to study all protein modifications?
Read the original research
Synthetic Proteins behind the Plasma Barrier: Molecular Spies.
Accounts of chemical research, 55(15), 2055-2067
Citation
Mann, Guy; Sadhu, Pradeep; Brik, Ashraf. (2022). Synthetic Proteins behind the Plasma Barrier: Molecular Spies.. Accounts of chemical research, 55(15), 2055-2067. https://doi.org/10.1021/acs.accounts.2c00236