Fatty acid photodecarboxylase is an ancient photoenzyme that forms hydrocarbons in the thylakoids of algae

Abstract

Fatty acid photodecarboxylase (FAP) is one of the few enzymes that require light for their catalytic cycle (photoenzymes). FAP was first identified in the microalga Chlorella variabilis NC64A, and belongs to an algae-specific subgroup of the glucose-methanol-choline oxidoreductase family. While the FAP from C. variabilis and its Chlamydomonas reinhardtii homolog CrFAP have demonstrated in vitro activities, their activities and physiological functions have not been studied in vivo. Furthermore, the conservation of FAP activity beyond green microalgae remains hypothetical. Here, using a C. reinhardtii FAP knockout line (fap), we showed that CrFAP is responsible for the formation of 7-heptadecene, the only hydrocarbon of this alga. We further showed that CrFAP was predominantly membrane-associated and that >90% of 7-heptadecene was recovered in the thylakoid fraction. In the fap mutant, photosynthetic activity was not affected under standard growth conditions, but was reduced after cold acclimation when light intensity varied. A phylogenetic analysis that included sequences from Tara Ocean identified almost 200 putative FAPs and indicated that FAP was acquired early after primary endosymbiosis. Within Bikonta, FAP was retained in secondary photosynthetic endosymbiosis lineages but absent from those that lost the plastid. Characterization of recombinant FAPs from various algal genera (Nannochloropsis, Ectocarpus, Galdieria, Chondrus) provided experimental evidence that FAP photochemical activity was present in red and brown algae, and was not limited to unicellular species. These results thus indicate that FAP was conserved during the evolution of most algal lineages where photosynthesis was retained, and suggest that its function is linked to photosynthetic membranes.

Salt induced oxidative stress alters physiological, biochemical and metabolomic responses of green microalga Chlamydomonas reinhardtii

“…Alkanes and alkenes are known as the main component of cuticular waxes in plants, preventing water loss and pathogen attacks etc ( Wicker-Thomas and Chertemps, 2010 ; Sorigué et al., 2016 ). Furthermore, microalgae alkanes and alkenes are synthesized in the chloroplast and are accumulated in membranes showing their different roles in cell growth, cell division, photosynthesis and stress tolerance to various stress factors including salinity ( Yamamori and Kageyama, 2018 ; Wichmann et al., 2020 ; Moulin et al., 2021 ).…”

Fatty Acid Photodecarboxylase Is an Interfacial Enzyme That Binds to Lipid–Water Interfaces to Access Its Insoluble Substrate

“…Because FAPv2 showed a preference for PA embedded in lipid bilayers (LUVs) and at the surface of a microemulsion, we further tested its ability to bind to model membranes consisting of monomolecular lipid films spread at the air−water interface and whose surface pressure was measured using a Langmuir film balance (Figure 7A). Because C. variabilis FAP is in vivo a chloroplast-localized enzyme that can partly associate with the thylakoid membrane fraction, 49 FAPv2 adsorption was first tested on a monolayer of total thylakoid lipids isolated from this microalga. FAPv2 was indeed found to adsorb onto thylakoid lipids (Figure 7B).…”

“…Thus, this plateau could be the IRS of FAP, involved in the interaction of FAP with ionized fatty acids and negatively charged interfaces like chloroplast membranes, 56 where FAP is partly located. 49 From the IRS location on one side of FAP and the direction of the dipolar moment vector, one can predict the possible orientation of FAP bound to membranes.…”

“…Specific experiments with increasing concentrations of a FA showing some solubility in water should be performed to demonstrate a putative interfacial activation of FAP. Nevertheless, because short to medium chain FAs are not found in C. variabilis from which FAP was isolated and because FAP was found to partition between the chloroplast stroma and thylakoid membranes, 49 FAP is likely to act exclusively as an interfacial enzyme in vivo.…”

Greenland Ice Sheet Surfaces Colonized by Microbial Communities Emit Volatile Organic Compounds

“…Recently, an enzyme belonging to an algae-specific subgroup of the glucose-methanol-choline oxidoreductase family, fatty acid photodecarboxylase (FAP), was identified ( Sorigué et al, 2017 ). FAP is one of the few known enzymes that requires light for their catalytic cycle and operates independently of photosystem II ( Moulin et al, 2021 ). Hence, both the stress caused by high levels of irradiance and the fact that a light-driven enzyme plays a role in hydrocarbon production point toward higher microbial volatile (hydrocarbon) production when irradiance is high.…”