TRISAFA · Transport of Reaction Intermediates in the Stepwise Assembly of Fatty Acids

Transport of Reaction Intermediates in the Stepwise Assembly of Fatty Acids

De novo fatty acid synthesis is crucial for metabolism, supplying molecules for energy storage, cell wall structure, and signaling. Saturated fatty acids are synthesized through sequential enzymatic reactions, adding two carbons at a time. In animals, fungi, and some bacteria, these enzymes form type I fatty acid synthases (FAS), large multifunctional assemblies with high efficiency. This has motivated extensive research into the use of FAS for biotechnological applications, in particular the production of medium-chain fatty acids, precursors for the production of biofuels. The structural organization of the FAS is critical for its catalytic turnover rate. In the fungal FAS, the enzymatic domains are expressed on two distinct polypeptides, the α- and β-subunits. These subunits assemble into a barrel-shaped α6β6 oligomer. The oligomer is bisected by a central disk formed by the α-subunits, while the β-subunits are arranged on either side of the central disk enclosing two hemispherical reaction chambers. The catalytic sites are located in the lumen of the reaction chamber. An integral acyl carrier protein (ACP) facilitates the transfer of reaction intermediates between the catalytic sites. This ensures that there is a sufficient local concentration of the reaction intermediates and allows the synthesis to proceed in an efficient manner. Although substrate transfer is essential for enzymatic activity, very little is known about the process and how it is regulated at the molecular level. This is because substrate transfer is an inherently dynamic process, whereas traditional structural methods require stable intermediates. Thus, crucial transition between the enzymatic domains and the flexible hinge regions that connect the ACP to the FAS remain "invisible". Molecular dynamics (MD) simulations make it possible to simulate these processes. However, the size of the FAS and lack of well resolved intermediate states have made studies infeasible. However, recent advances in cryogenic electron microscopy have made it possible to resolve structures of the FAS with ACP bound to all enzymatic domains. These structures provide structural details about all functional intermediates of the fatty acid biosynthetic cycle and are an ideal starting point for large-scale molecular dynamics simulations. Specifically, the goal of this project was to address central questions of fatty acid biosynthesis: 1) How do conformational changes prime fatty acid synthesis? 2) What factors influence the stochastic motion of ACP during elongation? These questions are not only central to understanding the function of the FAS. They can also provide the basis for further exploitation of the FAS for biotechnological applications.

Data: CORDIS, © European Union