Euglena gracilis and Trypanosomatids Possess Common Patterns in Predicted Mitochondrial Targeting Presequences

Abstract

Euglena gracilis possessing chloroplasts of secondary green algal origin and parasitic trypanosomatids Trypanosoma brucei, Trypanosoma cruzi and Leishmania major belong to the protist phylum Euglenozoa. Euglenozoa might be among the earliest eukaryotic branches bearing ancestral traits reminiscent of the last eukaryotic common ancestor (LECA) or missing features present in other eukaryotes. LECA most likely possessed mitochondria of endosymbiotic α-proteobacterial origin. In this study, we searched for the presence of homologs of mitochondria-targeted proteins from other organisms in the currently available EST dataset of E. gracilis. The common motifs in predicted N-terminal presequences and corresponding homologs from T. brucei, T. cruzi and L. major (if found) were analyzed. Other trypanosomatid mitochondrial protein precursor (e.g., those involved in RNA editing) were also included in the analysis. Mitochondrial presequences of E. gracilis and these trypanosomatids seem to be highly variable in sequence length (5-118 aa), but apparently share statistically significant similarities. In most cases, the common (M/L)RR motif is present at the N-terminus and it is probably responsible for recognition via import apparatus of mitochondrial outer membrane. Interestingly, this motif is present inside the predicted presequence region in some cases. In most presequences, this motif is followed by a hydrophobic region rich in alanine, leucine, and valine. In conclusion, either RR motif or arginine-rich region within hydrophobic aa-s present at the N-terminus of a preprotein can be sufficient signals for mitochondrial import irrespective of presequence length in Euglenozoa.

Role of Δ1-Pyrroline-5-Carboxylate Dehydrogenase Supports Mitochondrial Metabolism and Host-Cell Invasion of Trypanosoma cruzi

“…In eukaryotes, these enzymes are located in the mitochondria and may participate in other redox processes that occur inside this organelle (70). Although the TcP5CDH N terminus could not be accurately predicted as an mTP using conventional bioinformatic tools, a detailed analysis revealed an N-terminal region (MLRR and FAFAYA motifs and an ␣-helix spanning the mitochondrial membrane) with protein fingerprints that are characteristic of an mTP for mitochondrial proteins in trypanosomes (67). Once imported, this mTP can be removed by mitochondrial peptidases (Gi: 71655600, 71420779 in Table 4 our mitochondrial preparations.…”

The Mitochondrion of Euglena gracilis

“…The presequences in E. gracilis can be divided into two types: i) short (up to 10 amino acids long) and ii) long (10-30 amino acids) -although some presequences can be longer (up to 118 amino acids). It was not possible to find predicted cleaved presequences in all analyzed mitochondrial proteins of E. gracilis, although they were predicted to be targeted to mitochondria (Krnáčová et al 2012), similar to hydrogenosomes of Trichomonas vaginalis, where the majority of hydrogenosomal proteins do not harbor an N-terminal targeting sequence (Garg et al 2015).…”

“…Recently a protein assumed to have the same function as Tom40 in eukaryotes (Zársky et al 2012) was found in trypanosomes: ATOM (Pusnik et al 2011), but it was not found in the transcriptomes of euglenids (Krnáčová et al 2012). The mitochondrial proteins of Euglena possess presequences with a common (M/L)RR motif at the N-terminus or within the presequence for the organellar targeting (Krnáčová et al 2012), as in some trypanosomatid mitochondrial proteins (Häusler et al 1997). The presequences seem to be highly variable in sequence length (5-118 amino acids) with an average size of 31-41 amino acids, but apparently share statistically significant similarities.…”

“…The mitochondrial import apparatus of Euglenozoa is supposed to be primitive; most components of the canonical mitochondrial import machinery could not be identified in euglenozoan sequences -including Tom40 (Schneider et al 2008). Recently a protein assumed to have the same function as Tom40 in eukaryotes (Zársky et al 2012) was found in trypanosomes: ATOM (Pusnik et al 2011), but it was not found in the transcriptomes of euglenids (Krnáčová et al 2012). The mitochondrial proteins of Euglena possess presequences with a common (M/L)RR motif at the N-terminus or within the presequence for the organellar targeting (Krnáčová et al 2012), as in some trypanosomatid mitochondrial proteins (Häusler et al 1997).…”

“…The presequences seem to be highly variable in sequence length (5-118 amino acids) with an average size of 31-41 amino acids, but apparently share statistically significant similarities. In most presequences the (M/L)RR motif is followed by a positively charged, hydrophobic region rich in alanine, leucine, and valine (Krnáčová et al 2012). The presequences in E. gracilis can be divided into two types: i) short (up to 10 amino acids long) and ii) long (10-30 amino acids) -although some presequences can be longer (up to 118 amino acids).…”