Mitochondria are essential constituents of every eukaryotic cell. Like many other cellular compartments the molecular structure of the secluded interior of mitochondria is difficult to study by conventional structural biology approaches. Recent revolutionary technological and methodological developments now enable detailed structural studies of macromolecular complexes in their native settings using cryo-electron tomography (Cryo-ET). This approach allows studying processes that are difficult to analyze in isolation, in particular those involving membrane-associated complexes, and it can reveal the native supramolecular organization of macromolecular machines. Mitochondria with their limited proteome of ~1,000 proteins and their restricted spatial dimensions are uniquely suited to establish a groundbreaking ‘holistic’ approach to structural biology.
Key to mining biological information from CET images (tomograms), which have a very low signal-to-noise ratio, is computational analysis. We actively develop a computational workflow for in situ structural biology, involving localization of macromolecules in tomograms with high specificity and determining their high-resolution structure by subtomogram averaging. We apply this approach to elucidate the biogenesis of proteins of the inner mitochondrial membrane (IMM) in yeast and humans. In addition to its importance for basic biology we anticipate that our structural data will contribute to our mechanistic understanding of age-related pathologies, including neurodegenerative diseases, diabetes mellitus and cancer.