Two parameters improve efficiency of mitochondrial uptake of adenylate kinase: decreased folding velocity and increased propensity of N-terminal alpha-helix formation.
The long isoform of eukaryotic adenylate kinase has a dual subcellular location in the cytoplasm and in the mitochondrial intermembrane space. Protein sequences and modifications are identical in both locations. In yeast, the bulk of the major form of adenylate kinase (Aky2p) is in the cytoplasm and, in the steady state, only 5-8% is sorted to the mitochondrial intermembrane space. Since the reasons for exclusion from mitochondrial import are unclear, we have constructed aky2 mutants with elevated mitochondrial uptake efficiency of Aky2p in vivo and in vitro. We have analyzed the effect of the mutations on secondary structure prediction in silico and have tested folding velocity and folding stability. One type of mutants displayed decreased proteolytic stability and retarded renaturation kinetics after chaotropic denaturation implying that deterioration of folding leads to prolonged presentation of target information to mitochondrial import receptors, thereby effecting improved uptake. In a second type of mutants, increased import efficiency was correlated with an increased probability of formation of an alpha-helix with increased amphipathic moment at the N-terminus suggesting that targeting interactions with mitochondrial import receptors had been improved at the level of binding affinity.
Angermayr
M
M
Institut für Genetik und Mikrobiologie der Universität München, Maria-Ward-Strasse 1a, D-80638, Munich, Germany.
Strobel
G
G
Zollner
A
A
Korber
D
D
Bandlow
W
W
D000263:Adenylate Kinase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004792:Enzyme Precursors / Q000378:metabolism; D004795:Enzyme Stability; D007425:Intracellular Membranes / Q000201:enzymology; D008564:Membrane Potentials; D008928:Mitochondria / Q000201:enzymology*; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D011489:Protein Denaturation; D017510:Protein Folding; D020673:Protein Renaturation; D017433:Protein Structure, Secondary; D021381:Protein Transport; D014634:Valinomycin / Q000494:pharmacology; D015003:Yeasts / Q000201:enzymology / Q000235:genetics
D004792:Enzyme Precursors; D014634:Valinomycin; D000263:Adenylate Kinase