Chlamydomonas carries out fatty acid β‐oxidation in ancestral peroxisomes using a bona fide acyl‐CoA oxidase

Abstract

SummaryPeroxisomes are thought to have played a key role in the evolution of metabolic networks of photosynthetic organisms by connecting oxidative and biosynthetic routes operating in different compartments. While the various oxidative pathways operating in the peroxisomes of higher plants are fairly well characterized, the reactions present in the primitive peroxisomes (microbodies) of algae are poorly understood. Screening of a Chlamydomonas insertional mutant library identified a strain strongly impaired in oil remobilization and defective in Cre05.g232002(CrACX2), a gene encoding a member of the acyl-CoA oxidase/dehydrogenase superfamily. The purified recombinant CrACX2 expressed in Escherichia coli catalyzed the oxidation of fatty acyl-CoAs into trans-2-enoyl-CoA and produced H 2 O 2 . This result demonstrated that CrACX2 is a genuine acyl-CoA oxidase, which is responsible for the first step of the peroxisomal fatty acid (FA) β-oxidation spiral. A fluorescent protein-tagging study pointed to a peroxisomal location of CrACX2. The importance of peroxisomal FA β-oxidation in algal physiology was shown by the impact of the mutation on FA turnover during day/night cycles. Moreover, under nitrogen depletion the mutant accumulated 20% more oil than the wild type, illustrating the potential of β-oxidation mutants for algal biotechnology. This study provides experimental evidence that a plant-type FA β-oxidation involving H 2 O 2 -producing acyl-CoA oxidation activity has already evolved in the microbodies of the unicellular green alga Chlamydomonas reinhardtii.

Lipid catabolism in microalgae

“…Differences in the compartmentation of FA β‐oxidation enzymes have been suggested as a consequence of different phylogenetic development. Owing to the limited literature on microalgal β‐oxidation, we focus our discussion here only on green microalgae, where peroxisomal FA β‐oxidation has recently been demonstrated through study of a Chlamydomonas mutant knocked‐out for an acyl‐CoA oxidase (Kong et al ., ).…”

“…We have recently isolated and characterized a knockout mutant for ACX2. The acx2 mutant is impaired in oil remobilization upon N resupply (Kong et al ., ). Oil remobilization is severely (60–80%) but not completely blocked in acx2 , suggesting functional redundancy with the other four ACXs (Li‐Beisson et al ., ).…”

“…During the N recovery, lipid catabolism is important to degrade TAG storage to supply cells with carbon precursors for synthesis of structural membranes. Moreover, FA β‐oxidation is found to be important in regulating the amount of FAs during day/night cycles, and is essential for FA utilization upon carbon starvation (Kong et al ., ). In addition, lipid turnover has also been found to contribute to resource allocation during aging or senescence in land plants (Troncoso‐Ponce et al ., ).…”

Metabolic modelling and simulation of the light and dark metabolism of Chlamydomonas reinhardtii

“…In iCre1355 metabolic network the first reaction in β‐oxidation is assigned to acyl‐CoA oxidase (EC 1.3.3.6). This is consistent with the recently observed impaired oil remobilization in an isolate of C. reinhardtii having a defective gene for an enzyme of the acyl‐CoA oxidase/dehydrogenase superfamily (Kong et al ., ). For this defective isolate, the first step of fatty acid β‐oxidation was shown to be due to H 2 O 2 ‐producing oxidation of acyl‐CoA (Kong et al ., ).…”

“…This is consistent with the recently observed impaired oil remobilization in an isolate of C. reinhardtii having a defective gene for an enzyme of the acyl‐CoA oxidase/dehydrogenase superfamily (Kong et al ., ). For this defective isolate, the first step of fatty acid β‐oxidation was shown to be due to H 2 O 2 ‐producing oxidation of acyl‐CoA (Kong et al ., ). Although the acyl‐CoA oxidases require FAD, as considered in iCre1355, the model omits the oxidative half of the reaction.…”