A MITOCHONDRIAL-LIKE TARGETING SIGNAL ON THE HYDROGENOSOMAL MALIC ENZYME FROM THE ANAEROBIC FUNGUS NEOCALLIMASTIX FRONTALIS - SUPPORT FOR THE HYPOTHESIS THAT HYDROGENOSOMES ARE MODIFIED MITOCHONDRIA

The hydrogenosomal malic enzyme (ME) was purified from the anaerobic f ungus Neocallimastix frontalis. Using reverse genetics, the correspond ing cDNA was isolated and characterized. The deduced amino acid sequen ce of the ME showed high similarity to ME from metazoa, plants and pro tists. Putative functional domains for malate and NAD(+)/NADP(+) bindi ng were identified. Phylogenetic analysis of the deduced amino acid se quence of the new ME suggests that it is homologous to reference bacte rial and eukaryotic ME. Most interestingly, the cDNA codes for a prote in which contains a 27-amino-acid N-terminus which is not present on t he purified mature protein. This presequence shares features with know n mitochondrial targeting signals, including an enrichment in Ala, Leu , Ser, and Arg, and the presence of an Arg at position -2 relative to amino acid 1 of the mature protein. This is the first report of a mito chondrial-like targeting signal on a hydrogenosomal enzyme from an ana erobic fungus and provides support for the hypothesis that hydrogenoso mes in Neocallimastix frontalis might be modified mitochondria.