Abstract 1522 A dynamin-like pseudoenzyme coordinates with MICOS to promote mitochondrial cristae architecture

Mitochondrial respiratory function is highly dependent on the organization of the inner membrane into morphological domains, including the organelle's hallmark cristae membranes. Cristae are formed in part by the highly conserved Mitochondrial Contact Site and Cristae Organizing System (MICOS) complex. However, the precise mechanistic role of each MICOS subunit and how MICOS coordinates with other cristae shaping factors remains poorly understood. Here, we examine the MICOS complex in Schizosaccharomyces pombe, a minimal model whose genome only encodes for four core subunits. Using an unbiased proteomics approach, we identify a poorly characterized inner mitochondrial membrane protein that interacts with MICOS and is required to maintain cristae morphology, which we name Mmc1. We demonstrate that Mmc1 localizes with MICOS at cristae junctions and additively works in concert with MICOS to promote normal mitochondrial morphology and respiratory function. Bioinformatic analyses reveal that Mmc1 is a distant relative of the Dynamin-Related Protein (DRP) family of GTPases, which are well established to shape and remodel membranes. We find that, like DRPs, Mmc1 self-associates and forms high molecular weight assemblies. Interestingly, however, Mmc1 is a pseudoenzyme that lacks key residues required for GTP binding and hydrolysis, suggesting it does not dynamically remodel membranes. Instead, we speculate that Mmc1 adopts an assembled DRP-like fold to generate or stabilize local membrane curvature. These data are consistent with a model in which Mmc1 stabilizes cristae architecture by acting as a scaffold to support cristae ultrastructure on the matrix side of the inner membrane. Our study reveals a new class of cristae-maintaining proteins and highlights the possibility that functionally analogous proteins work with MICOS to establish cristae morphology in metazoans. J.R.F. is supported by a grant from the NIH (R35GM137894) and the UT Southwestern Endowed Scholars Program. M.L.R. is supported by grants from the NIH (R21AI171227 & R01AI150715), Welch foundation (I-2075-20210327), and a Burroughs Wellcome Fund PATH award (1021959).