Euglena Central Metabolic Pathways and Their Subcellular Locations

Abstract

Euglenids are a group of algae of great interest for biotechnology, with a large and complex metabolic capability. To study the metabolic network, it is necessary to know where the component enzymes are in the cell, but despite a long history of research into Euglena, the subcellular locations of many major pathways are only poorly defined. Euglena is phylogenetically distant from other commonly studied algae, they have secondary plastids bounded by three membranes, and they can survive after destruction of their plastids. These unusual features make it difficult to assume that the subcellular organization of the metabolic network will be equivalent to that of other photosynthetic organisms. We analysed bioinformatic, biochemical, and proteomic information from a variety of sources to assess the subcellular location of the enzymes of the central metabolic pathways, and we use these assignments to propose a model of the metabolic network of Euglena. Other than photosynthesis, all major pathways present in the chloroplast are also present elsewhere in the cell. Our model demonstrates how Euglena can synthesise all the metabolites required for growth from simple carbon inputs, and can survive in the absence of chloroplasts.

A Uniquely Complex Mitochondrial Proteome from Euglena gracilis

“…2005 ). Recent investigations into the subcellular compartmentalization of metabolic pathways in E. gracilis have been lacking extensive proteomic information on the mitochondria ( Inwongwan et al. 2019 ), which we hope to rectify here.…”

Metabolic quirks and the colourful history of the Euglena gracilis secondary plastid

“…A direct Blast search of the whole transcriptome confirmed that the enzymes of amino acid biosynthesis are indeed present ( E. gracilis does not require supplementation by any amino acid when grown autotrophically on minimal medium; Hall & Schoenborn, ), but their localisation is nonplastidial, in agreement with the previous in silico prediction (Ebenezer et al ., ). Possible exceptions are shikimate kinase (seqid 11810) (Inwongwan et al ., ), which exhibits the typical plastidial targeting signal, and an enzyme in the shikimate pathway, 5‐enolpyruvylshikimate‐3‐phosphate synthase, which has been previously shown to localise in the E. gracilis plastid (Reinbothe et al ., ). However, the former was not detected in the plastid fraction, and the latter is absent from the transcriptome.…”

“…The current state of knowledge regarding metabolic pathway localisation in Euglena is largely based on biochemical experiments and in silico prediction (recently reviewed by Inwongwan et al, 2019). In this study, we rely on a comprehensive proteomic dataset to reconstruct metabolic pathways localised in the E. gracilis plastid.…”

Glycosylated proteins identified for the first time in the alga Euglena gracilis

“…In order to identify the likely subcellular location of these abundant proteins, protein targeting predictions were performed, using bioinformatic tools that have previously been used for Euglena proteins. 4 Protein transport into Euglena chloroplasts occurs first via the secretory pathway and the Golgi apparatus using a secretion signal, followed by targeting to the chloroplast using a plastid targeting signal. 20 Therefore, to confirm whether a protein was truly secreted or sent to the chloroplast, any predicted signal peptides were removed and the prediction repeated, revealing any masked plastid targeting signal.…”

“…3 Uniquely among plastid containing cells, the chloroplast can be lost from photosynthetic Euglena without compromising their viability, due to duplication of all major pathways present in the chloroplast elsewhere in the cell. 4 Euglenids are related to the well-known Kinetoplastid unicellular parasites Trypanosoma and Leishmania , as part of the phylum Euglenozoa. 5 Euglena have been subject to scientific study for hundreds of years, but have recently become more intensely researched due to their considerable potential for biotechnological exploitation.…”