The Structure of an Aldehyde Decarbonylase from Prochlorococcus Marinus Implicated in Biofuel Synthesis Indicates an Octadecanoic Acid Ligand Coordinated to a Di-Iron Catalytic Center∗

Abstract

Prochlorococcus marinus, a prevalent marine cyanobacterium, can use sunlight and atmospheric CO2 to convert fatty-acid like precursors into alkane biofuels. Schirmer et al. (Science, 2010) showed that alkane production in cyanobacteria entails a two-enzyme process in which the acyl-CoA moiety is reduced to an aldehyde followed by decarbonylation to an alkane. The structure of the aldehyde decarbonylase has been determined by the Joint Center for Structural Genomics (PDB ID 2oc5). Here, we have identified the bound metals at the catalytic site as Fe and, based on the results of crystallographic refinement, have assigned a previously unidentified ligand as an octadecanoic acid. The metal identity was determined from X-ray fluorescence and anomalous difference Fourier maps. The oxygen atoms of the octadecanoic acid are within coordination distance of the Fe atoms and the hydrocarbon tail extends into the interior of the protein. Previous studies showed the enzyme can use octadecanal as a substrate, but the structure raises the question if it can directly catalyze alkane formation from octadecanoic acid ∗Supported by NIGMS PSI grants U54 GM094586 and GM074898View Large Image | View Hi-Res Image | Download PowerPoint Slide