THE STRUCTURE OF BOVINE MITOCHONDRIAL ADENYLATE KINASE - COMPARISON WITH ISOENZYMES IN OTHER COMPARTMENTS

In vertebrates, there are different adenylate kinases in the compartme nts cytosol, mitochondrial intermembrane space, and mitochondrial matr ix. Here, we report the spatial structure of the intermembrane species established in two crystal forms by X-ray diffraction analyses at 1.9 2 and 2.1 Angstrom resolution. In both structures, the enzyme is unlig ated, and thus in an ''open'' conformation. The enzyme was prepared fr om bovine liver, containing at least five variants arisen from posttra nscriptional and posttranslational modifications. It could only be cry stallized after removing some of these variants. A comparison with the known structures of the adenylate kinases from cytosol and mitochondr ial matrix reveals structural differences that should play a role in p rotein targeting because none of these enzymes contains a cleavable si gnal peptide. A further comparison with adenylate kinases from Grampos itive bacteria showed that the structural Zn2+ ion of these species is replaced by a strictly conserved assembly of hydrogen bonded residues .