FUNGAL FERRITINS

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As relatively simple eukaryotes, fungi appear to have aspects to their iron metabolism that are related to both other microbial (prokaryotic) systems as well as those of the higher eukaryotes. Thus its study can tell us something of the evolutionary development of iron metabolism as well as providing a simpler model of mammalian iron transport and storage and regulation. In addition, the Zygomycetes group of fungi that we plan to study, contains a number of human fungal pathogens hence a more detailed knowledge of this important part of their metabolism may lead to advances in therapy. In our preliminary work, two distinct ferritin-like iron containing proteins have been identified and isolated from the fungus Absidia spinosa; one from the spores and another from the mycelia. The mycelial protein has been purified and consists of two subunits of Ca. 20 kD molecular weight. Based on the presence of a heme spectrum and the high degree of sequence homology found, it is established that the mycelial protein is a bacterioferritin. This is the first example demonstrating the presence of a bacterioferritin in a eukaryotic organism. The spore protein has not yet been purified to homogeneity but it is distinct by gel electrophoresis from the mycelial ferritin, does not appear to contain heme, and has Mossbauer parameters suggestive of a "mammalian" like ferritin core. We plan to isolate the genes coding for both forms of the fungal ferritins, overexpress them and study some of their biophysical properties related to iron core formation. The observation that the "bacterio" type and "conventional" types of ferritin both exist in fungi but in different developmental forms also opens the way for detailed study of the function and regulation of these two proteins in a way that has not been possible in other classes of organisms.