Le T H, Blair D, McManus D P
Molecular Parasitology Unit, Australian Centre for International and Tropical Health and Nutrition, Queensland Institute of Medical Research and University of Queensland, 300 Herston Road, Brisbaner, Qld 4029, Australia.
Biochim Biophys Acta. 2001 Apr 7;1546(2):435-43. doi: 10.1016/s0167-4838(01)00156-x.
Sequence-specific DNA-binding proteins are characterised by short coiled-coil structural domains classified as zinc finger/RING finger, leucine zipper (L-Zip) or helix-loop-helix (HLH) motifs. The L-Zip proteins are defined by a pattern of at least four leucine (L) residues repeated every seventh amino acid that mediates protein dimerisation through the formation of parallel alpha-helical dimers. Usually the zipper is incorporated into a helix-loop-helix conformation called the basic helix-loop-helix-leucine zipper (bHLH/Zip). To date, all of the several hundred proteins reported as containing the L-Zip and/or bHLH/Zip motifs are nuclear-encoded. No leucine zipper polypeptide has, hitherto, been reported as mitochondrial in origin. Here we report such a polypeptide, the nicotinamide dehydrogenase subunit 4L (nad4L). We first identified this in human blood flukes of the genus Schistosoma (phylum Platyhelminthes; class Trematoda) but show that this is a common feature in other eucaryotes as well. Therefore, in addition to their well recognised role in oxidative phosphorylation, nad4L proteins may be pivotally involved in a range of other biological processes such as transcription and/or replication activation or as signal transmitters in communication with the nucleus and other cellular organelles. This may indicate a link between transcription regulation and respiration in mitochondria. We have also identified L-Zip-like motifs in nuoK, the procaryotic equivalent of the nad4L mitochondrial protein.
