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.

The Crystal Structure of a Mammalian Fatty Acid Synthase

Nonribosomal peptide synthetases: structures and dynamics.

Biosynthesis of polyketides by trans-AT polyketide synthases

Certain bacterial enzymes are packaged within protein chambers that provide a confined environment for their reactions to take place. Ban and colleagues now identify a family of proteins that form nanocompartments, similar to bacterial microcompartments such as the carboxysome, and show that the enzymes within are anchored by their C-terminal extensions to binding sites on the inner surface of the chamber. Compartmentalization is an important organizational feature of life. It occurs at varying levels of complexity ranging from eukaryotic organelles and the bacterial microcompartments, to the molecular reaction chambers formed by enzyme assemblies. The structural basis of enzyme encapsulation in molecular compartments is poorly understood. Here we show, using X-ray crystallographic, biochemical and EM experiments, that a widespread family of conserved bacterial proteins, the linocin-like proteins, form large assemblies that function as a minimal compartment to package enzymes. We refer to this shell-forming protein as 'encapsulin'. The crystal structure of such a particle from Thermotoga maritima determined at 3.1-A resolution reveals that 60 copies of the monomer assemble into a thin, icosahedral shell with a diameter of 240 A. The interior of this nanocompartment is lined with conserved binding sites for short polypeptide tags present as C-terminal extensions of enzymes involved in oxidative-stress response.

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Structural basis of enzyme encapsulation into a bacterial nanocompartment

Triacylglycerols are among the most attractive alternative raw materials for biofuel development. Current oil plant-based technologies are limited in terms of triacylglycerol production capacity and rate. These limitations may be circumvented by biotransformation of carbohydrates into lipids; however, our understanding of microbial oleaginicity remains limited. Here we present the results of a multi-omic analysis of Rhodosporidium toruloides, a robust triacylglycerol-producing fungus. The assembly of genome and transcriptome sequencing data reveals a genome of 20.2 Mb containing 8,171 protein-coding genes, the majority of which have multiple introns. Genes including a novel fatty acid synthase are predicted to participate in metabolic pathways absent in non-oleaginous yeasts. Transcriptomic and proteomic data suggest that lipid accumulation under nitrogen-limited conditions correlates with the induction of lipogenesis, nitrogenous compound recycling, macromolecule metabolism and autophagy. The multi-omic map of R. toruloides therefore provides a valuable resource for efforts to rationally engineer lipid-production pathways. The ability of oleaginous fungi to produce lipids for biofuels remains untapped, in part due to a lack of genetic information required to engineer industrial strains. Zhuet al. present the genome of R. toruloides, and identify transcriptomic and proteomic changes associated with lipid production.

/pdf/a-multi-omic-map-of-the-lipid-producing-yeast-rhodosporidium-3jw9kq0dan.pdf

A multi-omic map of the lipid-producing yeast Rhodosporidium toruloides

We report crystal structures of the 2.6-megadalton α6β6 heterododecameric fatty acid synthase from Thermomyces lanuginosus at 3.1 angstrom resolution. The α and β polypeptide chains form the six catalytic domains required for fatty acid synthesis and numerous expansion segments responsible for extensive intersubunit connections. Detailed views of all active sites provide insights into substrate specificities and catalytic mechanisms and reveal their unique characteristics, which are due to the integration into the multienzyme. The mode of acyl carrier protein attachment in the reaction chamber, together with the spatial distribution of active sites, suggests that iterative substrate shuttling is achieved by a relatively restricted circular motion of the carrier domain in the multifunctional enzyme.

https://science.sciencemag.org/content/sci/316/5822/254.full.pdf

Bohdan Mikolásek

Papers

Structure of fungal fatty acid synthase and implications for iterative substrate shuttling.