Abstract
Cryptosporidium is a protozoan, apicomplexan, parasite that poses significant risk to humans and animals, as a common cause of potentially fatal diarrhea in immunodeficient hosts. The parasites have evolved a number of unique biological features that allow them to thrive in a highly specialized parasitic lifestyle. For example, the genome of Cryptosporidium parvum is highly reduced, encoding only 3,805 proteins, which is also reflected in its reduced cellular and organellar content and functions. As such, its remnant mitochondrion, dubbed a mitosome, is one of the smallest mitochondria yet found. While numerous studies have attempted to discover the function(s) of the C. parvum mitosome, most of them have been focused on in silico predictions. Here, we have localized components of a biochemical pathway in the C. parvum mitosome, in our investigations into the functions of this peculiar mitochondrial organelle. We have shown that three proteins involved in the mitochondrial iron‐sulfur cluster biosynthetic pathway are localized in the organelle, and one of them can functionally replace its yeast homolog. Thus, it seems that the C. parvum mitosome is involved in iron‐sulfur cluster biosynthesis, supporting the organellar and cytosolic apoproteins. These results spearhead further research on elucidating the functions of the mitosome and broaden our understanding in the minimalistic adaptations of these organelles.
Highlights
IntroductionRecent reports have functionally characterized these proteins in other protists, including Blastocystis (Tsaousis et al 2012) and microsporidia (Freibert et al 2017; Goldberg et al 2008)
Using BLASTP approach against various databases, we have identified a wide range of the components of the mitochondrial in the mitochondrial Fe-S cluster (ISC) machinery encoded by the C. parvum genome (Table S1)
ISC proteins were analyzed using four different prediction programs (Table S2). These analyses revealed that all algorithms were abled to predict localization of IscS and IscU proteins in the mitochondria of all Cryptosporidium species, with the exception of MitoProt, and Frataxin was not predicted to be mitochondrial
Summary
Recent reports have functionally characterized these proteins in other protists, including Blastocystis (Tsaousis et al 2012) and microsporidia (Freibert et al 2017; Goldberg et al 2008). To the best of our knowledge, the only studies on Fe-S cluster assembly machineries in apicomplexans have been focused on the apicoplast-localized SUF machinery in Plasmodium species (Charan et al 2017). With regard to the Fe-S cluster assembly machinery, the only published study demonstrated heterologous localization of the C. parvum sulfur donor protein IscS and the scaffold protein IscU in Saccharomyces cerevisiae mitochondria (LaGier et al 2003). Direct localization studies of this machinery in Cryptosporidium are nonexistent
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