Organelle-localized Self-assembly Of A Peptide Amphiphile

A new method to target the mitochondria of a cancer cell has been developed by researchers affiliated with the Ulsan National Institute of Science and Technology(UNIST). The research team expects that their study could pave way for new generation of anti-cancer drugs.

In-situ assembly of amphiphilic peptides with accompanying cellular functions inside a living cell (i.e., intracellular assembly) and their interaction with cellular components have been emerging as a versatile strategy in controlling cellular fate. However, achieving spatiotemporal control (i.e., inside cellular organelles or other sub-compartments) over the self-assembly of synthetic molecules inside the cell is challenging because of the difficulty of studying their behaviors in the complex intracellular environment.

In the study, led by Professor of Chemistry Ja-Hyoung Ryu at UNIST, the joint research team has introduced, for the first time, the organelle-localized self-assembly of a peptide amphiphile as a powerful strategy for controlling cellular fate.

Critical Aggregation Concentration

Self-assembly is an equilibrium process between the individual building units and their aggregated state, and the concentration of the molecules should be over the critical value to induce assembly (i.e., the critical aggregation concentration (CAC).

In living cells, achieving the CAC is also required to form assemblies of individual molecules, but has a limitation because the chemical complexity of cellular environments disrupts interactions among synthetic building units.

mitochondria

TEM images of mitochondria within the HeLa cell showing the morphological damage induced by Mito-FF.
Credit: UNIST

Intracellular self-assembly, thus, requires a higher concentration of the molecules than the CAC, which may limit the practical implementations of self-assembling molecules. Transformation of the molecular structure from hydrophilic to hydrophobic units inside the cell (or pericellular space) through external stimuli (chemical, or physical) is a powerful strategy to reduce the CAC by increasing the propensity for self-assembly.

However, chemical and physical stimuli (e.g., light, temperature, pH, and redox) are not relevant for intracellular assembly because they induce severe damage to cell.

Organelle-localization Induced Supramolecular Self-assembly

Professor Ryu’s research team introduced a specific cellular organelle-localization induced supramolecular self-assembly (OLISA) system could be a general strategy to induce self-assembly by raising local concentrations of the self-assembling molecules without additional treatment.

The small molecules readily diffuse through the cell membrane, reach to the target site (organelle or subcellular compartment depending on the targeting moiety), and then they undergo self-assembly inside the targeted organelle as a result of increased local concentration. The accumulation of molecules inside an organelle like mitochondria is ~500-1,000 times higher than that of extracellular space.

“OLISA is more general and direct strategy for achieving intracellular assembly and is entirely novel, it is a promising approach for controlling the cellular fate like apoptosis, cell proliferation etc. and is a useful strategy for their in depth investigations” says professor Ryu.

The design consists of mitochondria-accumulating amphiphilic peptide (Mito-FF), which consists of diphenylalanine as a β-sheet-forming building block, TPP as a mitochondrial targeting moiety, and pyrene as a fluorescent probe.

Mito-FF favorably accumulated in the mitochondria of cancer cells because of the high negative membrane potential and the increased concentration caused Mito-FF to self-assemble into a fibrous structure, whereas lack of fibril formation was observed in normal cells. The stiff Mito-FF fibrils destroyed the mitochondrial membrane and activated the intrinsic apoptotic pathway against cancer cells. This OLISA system offers a new approach for targeted cancer chemotherapy.

M.T. Jeena of Chemistry at UNIST, the lead author of the study, expects the new method to set the foundations for a new series of treatments that could maximize the healing process while minimizing side effects.

The work was funded by the National Research Foundation of Korea, and the Ulsan National Institute of Science and Technology research fund.

M. T. Jeena, L. Palanikumar, Eun Min Go, Inhye Kim, Myoung Gyun Kang, Seonik Lee, Sooham Park, Huyeon Choi, Chaekyu Kim, Seon-Mi Jin, Sung Chul Bae, Hyun Woo Rhee, Eunji Lee, Sang Kyu Kwak & Ja-Hyoung Ryu
Mitochondria localization induced self-assembly of peptide amphiphiles for cellular dysfunction
Nature Communications 8, Article number: 26 (2017) doi:10.1038/s41467-017-00047-z

Image: Intra-mitochondrial assembly of Mito-FF. Credit: UNIST

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