Bacterial Enoyl-Reductases: The Ever-Growing List of Fabs, Their Mechanisms and Inhibition

Enoyl-ACP reductases (ENRs) are enzymes that catalyze the last step of the elongation cycle during fatty acid synthesis. In recent years, new bacterial ENR types were discovered, some of them with structures and mechanisms that differ from the canonical bacterial FabI enzymes. Here, we briefly review the diversity of structural and catalytic properties of the canonical FabI and the new FabK, FabV, FabL, and novel ENRs identified in a soil metagenome study. We also highlight recent efforts to use the newly discovered Fabs as targets for drug development and consider the complex evolutionary history of this diverse set of bacterial ENRs

Overall structural comparison of xoFabV and ecFabI.

<p>The two structures differ dramatically. The β-sheet and the flanking α-helices are shifted, and xoFabV has additional secondary structures, including helices α1 and α11 – α13 and strands β5 – β8 and β11, which are shown in yellow. Other parts of xoFabV are shown in green; ecFabI is shown in magenta. (A) Side view. (B) Top view.</p

Full-length sequence alignment of three enoyl-ACP reductase enzymes from different organisms.

<p>The sequences are from <i>V. cholerae, B. mallei</i> and <i>X. oryzae</i>. Y226, Y236 and K245 of xoFabV and their corresponding residues in the other two enzymes are labelled with asterisks. V246 of xoFabV and its corresponding residues are labelled with a colon. The sequence alignment was performed using T-Coffee, and the figure was made using ESPript <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0026743#pone.0026743-Gouet1" target="_blank">[34]</a>.</p

Kinetic parameters for the wild-type xoFabV enzyme.

<p>Kinetic parameters for the wild-type xoFabV enzyme.</p

Structural comparison of the Y-X₈-K motif of xoFabV and the Y-X₆-K motif of ecFabI.

<p>Despite the fact that the Y-X₈-K motif of xoFabV has two more residues than the Y-X₆-K motif of ecFabI, the conformations of the conserved tyrosine and lysine residues are similar. The distance between the conserved tyrosine (Y236) and lysine (K245) residues in the Y-X₈-K motif of xoFabV (shown in green) is 10.4 Å, while the distance between Y156 and K163 in the Y-X₆-K motif of ecFabI (magenta) is 4.5 Å.</p

<i>In vivo</i> plasmid complementation test.

<p>The functions of the wild-type and mutant <i>xoFabV</i> genes were validated in the <i>E. coli fabI</i> (Ts) strain JP1111. Growth conditions at 30°C are before induction with arabinose; growth conditions at 42°C are after induction with arabinose.</p

Crystal structure of xoFabV.

<p>The structure consists of 13 α-helices and 11 β-strands, representing a classic Rossmann fold architecture. The secondary structures are shown in different colours and are labelled with the corresponding numbers. (A) Side view. (B) Top view. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0026743#pone-0026743-g001" target="_blank">Figures 1</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0026743#pone-0026743-g002" target="_blank"></a><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0026743#pone-0026743-g003" target="_blank"></a><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0026743#pone-0026743-g004" target="_blank">4</a> were made using PyMOL (DeLano Scientific, Palo Alto, California, USA; <a href="http://www.pymol.org" target="_blank">http://www.pymol.org</a>).</p

Progress curve analysis of the wild-type and mutant xoFabV variants in the NADH oxidation assay.

<p>The enzyme activity of wild-type and mutant xoFabV was determined by monitoring the oxidation of NADH to NAD⁺ at 340 nm. The reaction was initiated by adding the substrate crotonyl-CoA and was monitored for 10 min at 25°C.</p