The mitochondrial outer membrane protein hFis1 regulates mitochondrial morphology and fission through self-interaction

Mitochondrial fission in mammals is mediated by at least two proteins, DLP1/Drp1 and hFis1. DLP1 mediates the scission of mitochondrial membranes through GTP hydrolysis, and hFis1 is a putative DLP1 receptor anchored at the mitochondrial outer membrane by a C-terminal single transmembrane domain. The cytosolic domain of hFis1 contains six alpha-helices (alpha 1-alpha 6) out of which alpha 2-alpha 5 form two tetratricopeptide repeat (TPR) folds. In this study, by using chimeric constructs, we demonstrated that the cytosolic domain contains the necessary information for hFis1 function during mitochondrial fission. By using transient expression of different mutant forms of the hFis1 protein, we found that hFis1 self-interaction plays an important role in mitochondrial fission. Our results show that deletion of the alpha 1 helix greatly increased the formation of dimeric and oligomeric forms of hFis1, indicating that alpha 1 helix functions as a negative regulator of the hFisI self-interaction. Further mutational approaches revealed that a tyrosine residue in the alpha 5 helix and the linker between alpha 3 and alpha 4 helices participate in hFis1 oligomerization. Mutations causing oligomerization defect greatly reduced the ability to induce not only mitochondrial fragmentation by full-length hFis1 but also the formation of swollen ball-shaped mitochondria caused by alpha 1-deleted hFis1. Our data suggest that oligomerization of hFis1 in the mitochondrial outer membrane plays a role in mitochondrial fission, potentially through participating in fission factor recruitment. (C) 2008 Elsevier Inc. All rights reserved.