Structures of Tetrahymena’s respiratory chain reveal the diversity of eukaryotic core metabolism

Big complexes from single-celled eukaryoteMitochondria use a series of membrane-embedded enzymes to transform chemical energy first into an electrochemical gradient and then into ATP. The series of chemical steps that take place are conserved in aerobic organisms, but there is considerable structural divergence in different lineages. Working with extracted mitochondrial membranes, Zhou et al. determined structures of mitochondrial electron transfer chain complexes from a model ciliate (see the Perspective by Huynen and Elurbe). Complex I and a dimer of complex III form a supercomplex as in many other eukaryotes, but both have important fundamental differences in architecture and functional apparatus. Complex IV is massive relative to previously known structures, with more than half of the mass composed of components not seen in homologous structures, including mitochondrial carrier proteins and a translocase that may be involved in assembly or may be a relic of such components. —MAF