Mitochondrial Chemical Biology: New Probes Elucidate the Secrets of the Powerhouse of the Cell  Simon Wisnovsky, Eric K. Lei, Sae Rin Jean, Shana O. Kelley  Cell Chemical Biology  Volume 23, Issue 8, Pages 917-927 (August 2016) DOI: 10.1016/j.chembiol.2016.06.012 Copyright © 2016 Terms and Conditions

Figure 1 Potential Target Pathways for Mitochondrial Chemical Probes (1) Mitochondria encode for specific mitochondrial genes on a multi-copy circular genome, which is replicated and transcribed by mitochondrial specific machinery. Currently, our understanding of the factors involved in mtDNA replication and repair is incomplete. (2) Mitochondrial mRNAs are translated by the mitochondrial-specific translation machinery. A better understanding of mitochondrial translation could have an impact on the development of new therapeutics. (3) Proteins marked for degradation are digested by the mitochondrial protease ClpXP; little is known about the regulation of this pathway. (4) Proteins required for mitochondrial function not encoded by mtDNA are imported by the TIM/TOM import complex. By making other systems for import available, a more versatile arsenal of probes can be developed. (5) Mitochondrial energy production and membrane polarization are mediated by the electron transport chain. While this set of pathways has been characterized extensively, new probes that can interact with the ETC could be of use therapeutically. (6) Reactive oxygen species are produced by electron leaking from the ETC; characterizing the cellular reaction to mitochondrial ROS will enable us to better characterize the mechanisms of disease that are linked with ROS production. Cell Chemical Biology 2016 23, 917-927DOI: (10.1016/j.chembiol.2016.06.012) Copyright © 2016 Terms and Conditions

Figure 2 Mitochondria-Targeting Modalities for Delivery of Small-Molecule Probes (A) Mitochondria-penetrating peptides (MPPs). (B) Triphenylphosphonium (TPP). (C) Polymeric nanoparticle displaying TPP. Cell Chemical Biology 2016 23, 917-927DOI: (10.1016/j.chembiol.2016.06.012) Copyright © 2016 Terms and Conditions

Figure 3 Indicators of Mitochondrial Health Detectable with Chemical Probes (1) Mitochondrial superoxide and peroxide are normally detoxified but accumulate in damaged cells. (2) Exogenous overproduction of HClO can damage mitochondria. (3) High levels of peroxynitrite derived from the reaction of superoxide and nitric oxide can damage mitochondrial components. (4) Metal ions such as copper, zinc, iron, or magnesium, which are required as protein cofactors, can be released as free metal ions and contribute to mitochondrial damage. (5) Mitochondrial membrane potential is dissipated as a result of mitochondrial membrane disruption and mitochondrial dysfunction. Cell Chemical Biology 2016 23, 917-927DOI: (10.1016/j.chembiol.2016.06.012) Copyright © 2016 Terms and Conditions

Figure 4 New Strategies for High-Throughput Annotation of the Mitochondrial Proteome (A) Proximity-based ligation allows tagging of mitochondrial proteins with affinity labels and subsequent identification by mass spectrometry. (B) High-throughput genetic knockdown screening using small-molecule modulators of mitochondrial processes allows for identification of proteins with mitochondrial function. Cell Chemical Biology 2016 23, 917-927DOI: (10.1016/j.chembiol.2016.06.012) Copyright © 2016 Terms and Conditions