The Crystal Structure of a Mammalian Fatty Acid Synthase

Abstract

Mammalian fatty acid synthase is a large multienzyme that catalyzes all steps of fatty acid synthesis. We have determined its crystal structure at 3.2 angstrom resolution covering five catalytic domains, whereas the flexibly tethered terminal acyl carrier protein and thioesterase domains remain unresolved. The structure reveals a complex architecture of alternating linkers and enzymatic domains. Substrate shuttling is facilitated by flexible tethering of the acyl carrier protein domain and by the limited contact between the condensing and modifying portions of the multienzyme, which are mainly connected by linkers rather than direct interaction. The structure identifies two additional nonenzymatic domains: (i) a pseudo-ketoreductase and (ii) a peripheral pseudo-methyltransferase that is probably a remnant of an ancestral methyltransferase domain maintained in some related polyketide synthases. The structural comparison of mammalian fatty acid synthase with modular polyketide synthases shows how their segmental construction allows the variation of domain composition to achieve diverse product synthesis.

Structure and function of eukaryotic fatty acid synthases

“…The two regions are centrally connected and define two lateral clefts (Maier et al , 2008. The arrangement of domains in the 3D structure does not follow their linear order at the sequence level (Figs 12 and 16).…”

“…Crystals belong to the monoclinic space group P2 1 with unit cell dimensions of a=96 Å , b=245 Å , c=134 Å and b=101x, yielding a theoretical solvent content of 57 %. In spite of extensive optimization of crystallization conditions, the largest crystals obtained were thin plates and only 25 mm thick (Maier et al 2008). …”

“…15 a) and optimization of crystal stabilization that included temperature shifts prior to crystal freezing was required to obtain data to 3Á2 Å resolution necessary for building of an atomic model and refinement (Maier et al 2008). Furthermore, due to the small size and radiation sensitivity of crystals even when frozen, a multi-crystal data collection strategy was required to obtain a complete dataset : crystals were translated multiple times collecting about 5-10x of rotation per position, and data from several isomorphous crystals ) used for the rigid-body fitting of template domains, while the right panel depicts the experimental density after phase extension to 3Á2 Å resolution (Maier et al 2008) with alternative views of the same regions. This map was used for initial atomic model building of porcine FAS.…”

“…The animal FAS, in contrast to the fungal multienzyme, has no scaffold that tightly embeds the core enzymatic domains (Maier et al 2008). While the fungal FAS invests about 50 % of its total length into forming this scaffold, only 9 % of the total sequence are present in the form of linker regions in animal FAS.…”

Parsing Physiological Functions of Erythropoietin One Domain at a Time

“…This biologic strategy is actually employed in certain proteins with enzymatic activity. For example, fatty acid synthases are highly flexible proteins, where different domains actually move to accomplish interaction of the substrate with a key portion of the enzyme [9]. Molecular motors like dynein may have individual domains that are critical for certain tasks as they transport cargo down axons [10].…”