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Updated: Jun 27, 2025
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Analysis of Protein Folding, Transport, and Degradation in Living Cells by Radioactive Pulse Chase
Published on: February 12, 2019
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HOPS-Dependent Endosomal Escape Demands Protein Unfolding
Madeline Zoltek1, Angel L Vázquez Maldonado2, Xizi Zhang2
1Department of Molecular and Cell Biology, University of California, Berkeley, California 94720, United States.
ACS Central Science
|April 29, 2024
Summary
Protein delivery into cells is challenging. This study reveals that cargo unfolding is key for efficient endosomal escape using the ZF5.3 delivery system, guiding therapeutic design.
Area of Science:
- Biotechnology
- Cell Biology
- Drug Delivery
Background:
- Protein translocation across membranes is crucial for therapeutics but often inefficient.
- Endosomal escape is a major bottleneck in protein delivery, limiting cytosolic or nuclear access.
- Current delivery methods struggle with cargo variability and predictable efficiency.
Purpose of the Study:
- To elucidate the mechanism governing ZF5.3-mediated protein delivery efficiency.
- To identify cargo properties that dictate successful endosomal escape.
- To provide design principles for optimizing therapeutic protein translocation.
Main Methods:
- Utilized ZF5.3 mini-protein for cargo conjugation and delivery.
- Employed fluorescence correlation spectroscopy (FCS) for single-molecule analysis of intracytosolic concentration.
- Investigated the role of cargo unfolding properties (e.g., melting temperature, Tm) and size/pI.
Main Results:
- Cargo unfolding ability, not just size or charge, is critical for efficient ZF5.3-mediated delivery.
- Low-Tm cargoes (including intrinsically disordered proteins) utilize a high-efficiency pathway dependent on the homotypic fusion and protein sorting (HOPS) complex.
- Small protein domains achieve moderate delivery via the HOPS pathway, irrespective of their Tm.
Conclusions:
- ZF5.3 exploits a novel, HOPS-dependent endosomal escape pathway.
- Cargo unfolding is a critical determinant for efficient cytosolic delivery.
- These findings offer a rational basis for selecting or engineering therapeutic proteins for improved delivery.
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