Recently, a research team led by Prof. Xiaohong Fang from the Hangzhou Institute of Medicine of Chinese Academy of Sciences has developed a mitochondrial protease targeting chimera (MtPTAC) to address the challenge of protein regulation without ubiquitin-proteasome or lysosomal systems in membrane organelles such as mitochondria.
This study was published in Journal of the American Chemical Society.
MtPTAC is a bifunctional small molecule that can bind to mitochondrial caseinolytic protease P (ClpP) at one end and target protein at the other. Mechanistically, MtPTAC activates the hydrolase activity of ClpP while simultaneously bringing target proteins into proximity with ClpP. Taking mitochondrial RNA polymerase (POLRMT) as a model protein, this work demonstrated the powerful proteolytic ability and antitumor application prospects of MtPTAC, both in vivo and in vitro. This is the first modularly designed strategy that specifically hydrolyze target proteins inside mitochondria.
Protein expression level in eukaryotic cells is related to cell function and disease development. Targeted protein degradation (TPD) is an emerging technique for protein regulation. Currently, all TPD developed in eukaryotic cells relies on either ubiquitin-proteasome or lysosomal systems, thus are powerless against target proteins in membrane organelles lacking proteasomes and lysosomes, such as mitochondria. The mitochondrion is a double membrane organelle with a unique protein quality control system, and its matrix is proteasome-deficient. More than 1000 different proteins have been identified inside mitochondria. Numerous studies have confirmed that dysfunction of mitochondrial matrix protein plays a pivotal role in the occurrence and progression of several fatal diseases, such as neurodegenerative diseases and cancer. Developing new methods to degrade pathogenic proteins inside the mitochondrion is of great importance.
In this work, the researchers designed and developed a mitochondrial protease targeting chimera (MtPTAC) which consists of two small-molecule ligands linked by a PEG chain, to achieve the target degradation of a model protein in the mitochondrial matrix, the human mitochondrial RNA polymerase (POLRMT). Through MtPTAC, they explored a different approach from the existing degradation techniques. Regarding the protein degradation enzyme, the caseinolytic mitochondrial matrix peptidase proteolytic subunit (ClpP) was chosen, a serine protease widely distributed in mitochondria rather than the reported lysosome and ubiquitin-proteasome. Regarding the degradation mechanism, current degraders only bring the target protein into proximity to the degradation machine, but the ClpP ligand used in MtPTAC also directly enhances the hydrolytic activity of ClpP. The degradation of mitochondrial protein POLRMT led to tumor cell inhibition both in vitro and in vivo. In this work, a modular system was successfully established for mitochondrial protein proteolysis, which facilitates the general design as a platform strategy. Up to now, this is the first modular targeted degradation technique based on the protease system in eukaryotic cells.
Schematic diagram of the protein regulation of modular targeted degradation technique MtPTAC inside mitochondria
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