This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Removing a single amino acid can determine whether new proteins assemble into stable complexes within mitochondria. An enzyme carries out this precise trimming at the start of mitochondrial proteins.
Without it, numerous protein complexes lose their stability, according to a study led by Dr. Nora Vögtle of Heidelberg University and Dr. Pitter Huesgen of the University of Freiburg.
In their work published in Nature Structural & Molecular Biology, the scientists identified a previously unknown mechanism by which human cells maintain the balance of proteins in their mitochondria. Human cells contain various organelles that perform vital tasks. Mitochondria are central to energy production and are also involved in numerous metabolic and signaling processes.
Most mitochondrial proteins are made outside the organelle and then transported into it. For this journey, they carry a molecular address sequence at one end—the so-called N-terminus—which specialized enzymes remove after import. The proteins can then assemble into stable complexes and assume their mature, functional form.
An enzyme called ICP55 is involved in this maturation process. After another enzyme removes the address sequence at the N-terminus, ICP55 cleaves off exactly one additional amino acid. Until now, researchers did not know which proteins undergo both steps or what significance the second step has for human mitochondrial function.
The team led by Vögtle and Huesgen systematically investigated which imported proteins ICP55 processes and what happens when the enzyme is absent. Using proteomic methods, the researchers identified the mature N-termini of 446 mitochondrial proteins. They found 107 proteins that are targeted for processing by ICP55.
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