Euglena gracilis and Trypanosomatids possess common patterns in predicted mitochondrial targeting presequences

Area of Science:

• * Eukaryotic cell biology
• * Protist molecular biology
• * Mitochondrial biogenesis

Background:

• * Euglenozoa, including Euglena gracilis and trypanosomatids, represent early eukaryotic lineages with ancestral traits.
• * The last eukaryotic common ancestor (LECA) likely possessed mitochondria derived from endosymbiotic α-proteobacteria.
• * Understanding mitochondrial protein import in Euglenozoa provides insights into early eukaryotic evolution.

Purpose of the Study:

• * To identify homologs of mitochondria-targeted proteins in Euglena gracilis.
• * To analyze common motifs in N-terminal presequences of mitochondria-targeted proteins in Euglenozoa.
• * To investigate the role of these motifs in mitochondrial import.

Main Methods:

• * Searched EST datasets for mitochondria-targeted protein homologs in Euglena gracilis.
• * Analyzed N-terminal presequence motifs and compared them across Euglenozoa (E. gracilis, Trypanosoma brucei, Trypanosoma cruzi, Leishmania major).
• * Included analysis of trypanosomatid mitochondrial protein precursors, such as those involved in RNA editing.

Main Results:

• * Mitochondrial presequences in Euglenozoa exhibit significant length variability (5-118 amino acids) but share similarities.
• * A common (M/L)RR motif is frequently found at the N-terminus, likely mediating mitochondrial outer membrane import.
• * This motif can be located within the presequence, and is often followed by a hydrophobic region rich in alanine, leucine, and valine.

Conclusions:

• * Mitochondrial import signals in Euglenozoa are not solely dependent on presequence length.
• * The N-terminal (M/L)RR motif or an arginine-rich region within hydrophobic amino acids are sufficient for mitochondrial import.
• * These findings shed light on the conserved yet flexible mechanisms of mitochondrial protein targeting in early eukaryotes.