Fe-S Cluster Assembly in Oxymonads and Related Protists

Area of Science:

• Evolutionary biology
• Microbiology
• Biochemistry

Background:

• Monocercomonoides exilis, an oxymonad, is the first known eukaryote lacking mitochondria.
• Mitochondrial loss may have been facilitated by acquiring the prokaryotic SUF iron-sulfur (Fe-S) cluster assembly pathway, rendering the mitochondrial ISC pathway obsolete.

Purpose of the Study:

• To investigate the presence and distribution of Fe-S cluster biosynthesis pathways in oxymonads and related Preaxostyla species.
• To understand the evolutionary history and potential prokaryotic donors of the SUF pathway in these organisms.

Main Methods:

• Genomic and transcriptomic data analysis of six oxymonad species and relatives.
• Phylogenetic analyses to identify Fe-S cluster biosynthesis enzymes (ISC and SUF pathways).
• Examination of gene fusions, specifically SufDSU.

Main Results:

• No studied oxymonad or Preaxostyla species possesses the mitochondrial ISC pathway.
• All examined species contain the SUF pathway, indicating its acquisition preceded their last common ancestor.
• SufDSU proteins are fused in oxymonads and Paratrimastix pyriformis, suggesting specific prokaryotic donors like Firmicutes or Thermotogae.
• The downstream CIA pathway remains unaffected, implying the SUF pathway efficiently supports cytosolic and nuclear Fe-S protein maturation.

Conclusions:

• The transition from the ISC to the SUF Fe-S cluster assembly pathway is a conserved feature in Preaxostyla, preceding the loss of mitochondria in some lineages.
• The SUF pathway, potentially acquired from specific bacterial groups, successfully replaced the mitochondrial pathway without disrupting downstream processes.