Integrative structural modelling reveals the human Mic60-Mic19 subcomplex as a diffusion barrier in mitochondria

Abstract

Mitochondrial crista junctions (CJs) operate as regulated gateways into the cristae microenvironment, whose protein, metabolite, and ion compositions are finely tuned for mitochondrial function. The Mic60-Mic19 complex of the mitochondrial contact site and cristae organizing system (MICOS) complex was suggested to span across CJs and act as a diffusion barrier, but little is known of how its dynamic architecture facilitates this task. To address this question, we determine the crystal structure of an amino-terminal dimeric helical bundle of human Mic60. These and previous structural and biochemical data are harnessed in molecular dynamic (MD) simulations to develop a dynamic model of the human tetrameric Mic60-Mic19 subcomplex in the CJ environment, to validate its architecture using in organello and in vitro cross-linking data and to computationally characterize its function as a diffusion barrier. Our integrative structural biology approach enables the functional investigation of flexible, multidomain protein complexes which escape conventional structural methods. Mitochondrial crista junctions serve as entry points to cristae, with MICOS governing their form and composition. Here, authors resolve the dynamic structure of the human Mic60 subcomplex and how it spans across CJs to act as a diffusion barrier.