Research Article

An algal photoenzyme converts fatty acids to hydrocarbons

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Science  01 Sep 2017:
Vol. 357, Issue 6354, pp. 903-907
DOI: 10.1126/science.aan6349
  • Fig. 1 Identification of an alkane synthase in C. variabilis.

    (A) Number of proteins found after the final step in three independent purifications and list of the 10 proteins in common found by means of proteomic analysis. Proteins are ranked by decreasing spectral counts. (B) Predicted domains of the C. variabilis GMC oxidoreductase. (C) Chromatogram of the hydrocarbons produced (left) and immunoblot of the total proteins (right) in an E. coli strain expressing the C. variabilis GMC oxidoreductase (alkane synthase).

  • Fig. 2 Fatty acid decarboxylase activity of the C. variabilis alkane synthase.

    (A) Relative quantification of 13CO2 released upon incubation of 1-13C-palmitate with the purified recombinant enzyme. S, substrate; E, enzyme. (B) Relative activity of the purified recombinant enzyme on various free fatty acid substrates. Mean ± SD (n = 3 repeats).

  • Fig. 3 Light dependency of the C. variabilis alkane synthase.

    (A) Absorption spectrum and action spectrum of the purified enzyme. Mean ± SD (n = 3 repeats). The position of the flavin absorption maximum in the enzyme (467 nm) deviates from typical values (445 to 450 nm for most flavoproteins and free flavins). (B) Activity of the purified enzyme under successive light conditions. Activity on 1-13C-palmitate was monitored via release of 13CO2 by using membrane inlet mass spectrometry. (C) Dependence of the activity of the purified enzyme on white light intensity. Mean ± SD (n = 3 repeats). (D) Variation of total hydrocarbons in C. reinhardtii cells grown in a photobioreactor under blue and then red light. Mean ± SD (n = 3 repeats). FAMEs, fatty acid methyl esters.

  • Fig. 4 Structural features of the C. variabilis FAP.

    (A) Overall architecture of the enzyme in complex with FAD and palmitate (PLM). The structure is represented as an illustration colored from blue to red from the N to the C terminus, with the FAD and palmitic acid represented in stick. The long N-terminal helix is projected toward a noncrystallographic symmetry–related molecule that is not represented here for clarity. (B) Slice through the surface representation of the fatty acid photodecarboxylase. For clarity, small cavities in the interior of the enzyme are not shown. (C) Details of the palmitic acid–binding site with the side chains of residues within 4 Å of the substrate shown in stick. The omit map electron density associated to palmitic acid is also shown and contoured at 0.5σ (2Fo-Fc; blue) and 2σ (Fo-Fc; green). Single-letter abbreviations for the amino acid residues are as follows: A, Ala; C, Cys; D, Asp; E, Glu; F, Phe; G, Gly; H, His; I, Ile; K, Lys; L, Leu; M, Met; N, Asn; P, Pro; Q, Gln; R, Arg; S, Ser; T, Thr; V, Val; W, Trp; and Y, Tyr. (D) Distances (angstroms) between palmitic acid and FAD.

  • Fig. 5 Characterization of C. variabilis FAP by means of time-resolved spectroscopy.

    (A) Time-resolved fluorescence of FAP in the presence or absence of palmitic acid. (B) Absorption spectra of FAD•− [in glucose oxidase (31); red line] and oxidized FAD in FAP (solid black line), scaled assuming a molar absorption coefficient of 11 300 M−1cm−1 for the maximum of the absorption band in the blue (32). A red-shifted blue band of FAD in FAP (dotted black line) is shown to demonstrate the effect on the absorption at 515 nm. (C) Examples of transient absorption changes of FAP in the presence of excess substrate. Complementary data are shown in fig. S6. (D) Suggested model of the FAP photocycle. Directly observed intermediates and kinetics are shown in red.

  • Fig. 6 Unrooted phylogenetic tree of the GMC oxidoreductase family.

    The neighbor joining method was used. Species are abbreviated to three letters (one for the genus and two for the species epithet) (table S2). Proteins with demonstrated biochemical activity are indicated by three additional capital letters: AAO, aryl alcohol oxidase; AOX, alcohol oxidase; FAP, fatty acid photodecarboxylase; CBQ, cellobiose dehydrogenase; CHD, choline dehydrogenase; COX, cholesterol oxidase; CKO, compound K oxidase; FDH, fructose dehydrogenase; FOX, fructose oxidase; GDH, glucose dehydrogenase; GOX, glucose oxidase; HFO, hydroxy fatty acid oxidase (genetic evidence only); HNL, hydroxynitrile lyase; and POX, pyranose oxidase.

Supplementary Materials

  • An algal photoenzyme converts fatty acids to hydrocarbons

    D. Sorigué, B. Légeret, S. Cuiné, S. Blangy, S. Moulin, E. Billon, P. Richaud, S. Brugière, Y. Couté, D. Nurizzo, P. MuÌ^ller, K. Brettel, D. Pignol, P. Arnoux, Y. Li-Beisson, G. Peltier, F. Beisson*

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods
    • Figs. S1 to S12
    • Table S1
    • References

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