Research Group Leaders

Research

Biological membranes exhibit function-related shapes, leading to a plethora of complex and beautiful cell and cell organellar morphologies. Most if not all of these structures have evolved for a particular physiological reason. The shapes of these structures are formed by physical forces that operate on membranes. To create particular shaped cells and cell organelles, membranes must undergo deformations which are determined by the structure and elasticity of the membrane and this process is most probable driven by proteins, lipids and/or interplay of both. Therefore, an important question of current cell biology in conjunction with physics and mathematics is to elucidate the functional cause for these different membrane morphologies as well as how they are formed.
One of the most peculiar membrane shapes is observed in mitochondria. These organelles are surrounded by two membranes and especially the convoluted inner membrane displays a complex ultra-structure. A molecular understanding of how this membrane is shaped is missing to a large extent. Major structure giving elements of the inner membrane are the so-called cristae junctions. This short, tubular membrane segments connect the flat inner boundary membrane with the morphological dynamic cristae membranes. Cristae junctions are rather uniform with inner diameters between 15 – 35 nm and hence display high degrees of membrane curvature. They are thought to be important for cellular physiology as they help to maintain specific protein composition of inner membrane sub-domains. They are further implicated to play a major role during the intrinsic apoptotic pathway. Here, cristae junctions need to open to mobilize cytochrome c that is usually stored in intra-cristae spaces. Understanding how cristae junctions are formed and maintained or in other words, unraveling the molecular mechanisms of membrane remodeling at cristae junctions, is therefore of utmost importance. Unlike membrane remodeling in classical curvature-dependent processes like clathrin-mediated endocytosis, cristae junctions are most likely shaped by integral membrane proteins. At least some of these proteins are likely to be found within the MICOS complex (mitochondrial contact site and cristae organizing system). In recent years we were able to identify two inner membrane proteins that are part of the MICOS, with the ability to bend membranes at cristae junctions