Structural Studies on the Mitochondrial Fission Protein Fis1 Suggest a Mechanism of TPR Protein Self-Association

Abstract

Tetratricopeptide repeat (TPR) domains are protein-protein interaction domains present in all kingdoms of life and mutations of human TPR domains have been linked to disease. The TPR protein fission 1 (Fis1) is conserved in all species that contain mitochondria. In S. cerevisiae, Fis1 is essential for mitochondrial fission, acting as a scaffold for other fission proteins through its TPR domain. It remains unclear if the function of Fis1 is conserved in mammals. Fis1 oligomers exist in high molecular weight complexes on isolated mitochondria. However, the structural basis of these Fis1 oligomers remains largely unknown. The TPR and transmembrane domains of Fis1 have been shown to be essential for Fis1 oligomer formation on the mitochondrial membrane. We hypothesize that the ability of Fis1 to self-associate on the membrane is mediated by dimerization of the cytoplasmic domain and dimerization of the transmembrane domain. Here, we use biophysical and structural techniques to test this hypothesis. We demonstrate that Fis1 is able to self-associate via its cytoplasmic TPR domain and have developed reagents in order to reconstitute Fis1 in a membrane environment. This project will address the structure of the Fis1 oligomer on the membrane, which is an outstanding question in the field.