A quantitative method to track protein translocation between intracellular compartments in real-time in live cells using weighted local variance image analysis

A High-Resolution Luminescent Assay for Rapid and Continuous Monitoring of Protein Translocation across Biological Membranes

Protein translocation is a fundamental process in biology. Major gaps in our understanding of this process arise due the poor sensitivity, low time resolution and irreproducibility of translocation assays. To address this, we applied NanoLuc split-luciferase to produce a new strategy for measuring protein transport. The system reduces the timescale of data collection from days to minutes and allows for continuous acquisition with a time resolution in the order of seconds, yielding kinetics parameters suitable for mechanistic elucidation and mathematical fitting. To demonstrate its versatility, we implemented and validated the assay in vitro and in vivo for the bacterial Sec system and the mitochondrial protein import apparatus. Overall, this technology represents a major step forward, providing a powerful new tool for fundamental mechanistic enquiry of protein translocation and for inhibitor (drug) screening, with an intensity and rigor unattainable through classical methods.

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Conventional methods for monitoring protein translocation are laborious and discontinuous and lack kinetic detail.

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A split NanoLuc system was adapted for real-time monitoring of protein translocation through the bacterial Sec system and the mitochondrial Tim23 complex.

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The new assay reduces the timescale of data acquisition from days to minutes.

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It produces high-quality results suitable for kinetic fitting and model derivation.

Geometric compensation applied to image analysis of cell populations with morphological variability: a new role for a classical concept

Immunofluorescence is the gold standard technique to determine the level and spatial distribution of fluorescent-tagged molecules. However, quantitative analysis of fluorescence microscopy images faces crucial challenges such as morphologic variability within cells. In this work, we developed an analytical strategy to deal with cell shape and size variability that is based on an elastic geometric alignment algorithm. Firstly, synthetic images mimicking cell populations with morphological variability were used to test and optimize the algorithm, under controlled conditions. We have computed expression profiles specifically assessing cell-cell interactions (IN profiles) and profiles focusing on the distribution of a marker throughout the intracellular space of single cells (RD profiles). To experimentally validate our analytical pipeline, we have used real images of cell cultures stained for E-cadherin, tubulin and a mitochondria dye, selected as prototypes of membrane, cytoplasmic and organelle-specific markers. The results demonstrated that our algorithm is able to generate a detailed quantitative report and a faithful representation of a large panel of molecules, distributed in distinct cellular compartments, independently of cell’s morphological features. This is a simple end-user method that can be widely explored in research and diagnostic labs to unravel protein regulation mechanisms or identify protein expression patterns associated with disease.

Hexokinase II-derived cell-penetrating peptide targets mitochondria and triggers apoptosis in cancer cells

Overexpression of mitochondria-bound hexokinase II (HKII) in cancer cells plays an important role in their metabolic reprogramming and protects them against apoptosis, thereby facilitating their growth and proliferation. Here, we show that covalently coupling a peptide corresponding to the mitochondrial membrane–binding N-terminal 15 aa of HKII (pHK) to a short, penetration-accelerating sequence (PAS) enhances the cellular uptake, mitochondrial localization, and cytotoxicity of the peptide in HeLa cells. Further analysis revealed that pHK-PAS depolarized mitochondrial membrane potential, inhibited mitochondrial respiration and glycolysis, and depleted intracellular ATP levels. The effects of pHK-PAS were correlated with dissociation of endogenous full-length HKII from mitochondria and release of cytochrome c. Of significance, pHK-PAS treatment of noncancerous HEK293 cells resulted in substantially lower cytotoxicity. Thus, pHK-PAS effectively disrupted the mitochondria-HKII association in cancer cells, which led to mitochondrial dysfunction and, finally, apoptosis. Our results demonstrate the potential of the pHK-PAS cell-penetrating peptide as a novel therapeutic strategy in cancer.—Woldetsadik, A. D., Vogel, M. C., Rabeh, W. M., Magzoub, M. Hexokinase II–derived cell-penetrating peptide targets mitochondria and triggers apoptosis in cancer cells.