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The Core MICOS Complex Subunit mic60 has Been Substituted by Two Cryptic Mitofilin-containing Proteins in Euglenozoa.

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Summary

Mitochondrial MICOS complex protein Mic60 is replaced by Mic34 and Mic40 in Euglenozoa. These new proteins are crucial for mitochondrial and crista biogenesis, expanding our understanding of the mitofilin protein family.

Keywords:
MICOScristaemembrane remodelingmitochondrion

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Area of Science:

  • Cell Biology
  • Mitochondrial Biology
  • Evolutionary Biology

Background:

  • Cristae are mitochondrial subcompartments essential for cellular respiration, formed with the help of the Mitochondrial contact site and Cristae Organizing System (MICOS) complex.
  • The core MICOS protein, Mic60, is conserved from alphaproteobacterial ancestors and is vital for crista formation in most eukaryotes.
  • Euglenozoa, including trypanosomes, lack Mic60, suggesting an alternative mechanism for MICOS complex assembly and crista maintenance.

Purpose of the Study:

  • To investigate the replacement of Mic60 in Euglenozoa and identify the proteins responsible for MICOS complex function.
  • To elucidate the evolutionary divergence and functional roles of novel MICOS subunits in Euglenozoa.
  • To understand the impact of these divergent proteins on mitochondrial structure and biogenesis.

Main Methods:

  • Comparative genomics to identify Mic60 homologs in Euglenozoa.
  • Reverse genetics and protein interaction studies to characterize Mic34 and Mic40.
  • In vitro phospholipid binding assays.
  • Heterologous expression in bacteria and yeast to assess membrane remodeling.
  • Analysis of mitochondrial morphology in Trypanosoma brucei under varying conditions.

Main Results:

  • Mic60 is replaced by two distinct, divergent MICOS subunits, Mic34 and Mic40, in Euglenozoa.
  • Mic34 and Mic40 are not integral membrane proteins but are involved in the oxidative protein folding pathway essential for mitochondrial and crista biogenesis.
  • Mic34 binds phospholipid bilayers and, upon overexpression, elaborates the mitochondrion in Trypanosoma brucei, indicating a role in membrane remodeling.
  • Mutations in Mic34's mitofilin domain abolish its function, highlighting conserved functional motifs.

Conclusions:

  • The mitofilin protein family exhibits greater diversity than previously known, with Mic34 and Mic40 representing highly divergent members.
  • Euglenozoan MICOS complex assembly relies on these novel subunits, which have adapted to maintain mitochondrial function and crista structure.
  • This study reveals an alternative evolutionary trajectory for mitochondrial membrane organization and the MICOS complex.