Oral Presentation 2014 International Biophysics Congress

Mechanistic insight into mitofusin-mediated membrane fusion (#7)

Xiaoyu Hu 1 , Xiaofang Huang 1 , Quan Chen 1 , Junjie Hu 1
  1. Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, Tianjin, China

In eukaryotic cells, mitochondria divide and fuse constantly to maintain proper functions. The homotypic fusion of the outer mitochondrial membranes requires the mitofusin (MFN) proteins, a family of dynamin-like GTPases. MFN is anchored in the membrane by a hairpin of two closely spaced transmembrane (TM) segments, exposing both the N-terminal GTPase domain and the C-terminal tail (CT) to the cytosol. Such arrangement is very similar to that of the atlastin (ATL) GTPases, which mediates the homotypic fusion of the endoplasmic reticulum (ER) membranes. Here, we engineer various MFN-ATL chimeras to gain mechanistic insight into MFN-mediated fusion. We show that when the GTPase domain of MFN1 is replaced by the N-terminal cytosolic domain of ATL1, mitochondria fusion activities are retained. Similarly, when the cytosolic domains of MFN1 are anchored to the ER by the TMs of ATL1, ER morphology defects, caused by the lack of yeast ER fusogen, are restored in yeast cells. In addition, the TM segments of MFN1 form homotypic interactions, and the CT of MFN1 is exchangeable with that of ATL1, but does not mediate anti-parallel tethering as previously proposed. These results suggest that MFN is sufficient to mediate homotypic membrane fusion, utilizing conserved mechanisms similar to ATL.