Structure of mitochondrial creatine kinase

CREATINE kinase (CK; EC 2.7.3.2), an enzyme important for energy metabolism in cells of high and fluctuating energy requirements, catalyses the reversible transfer of a phosphoryl goup from phosphocreatine to ADP1–3. We have solved the structure of the octameric mitochondrial isoform, Mib-CK, which is located in the intermembrane compartment and along the cristae membranes. Mib-CK consumes ATP produced in the mitochondria for the production of phosphocreatine, which is then exported into the cytosol for fast regeneration of ATP by the eytosolic CK isoforms. The octamer has 422 point-group symmetry, and appears as a cube of side length 93 Å with a channel 20 Å wide extending along the four-fold axis. Positively charged amino acids at the four-fold faces of the octamer possibly interact with negatively charged mitochondrial membranes. Each monomer consists of a small α-helical domain and a large domain containing an eight-stranded antiparallel β-sheet flanked by seven α-helices. The conserved residues of the CK family form a compact cluster that covers the active site between the domains