Reconstruction of a fatty acid synthesis cycle from acyl carrier protein and cofactor structural snapshots

MTD: A cloud-based omics database and interactive platform for Myceliophthora thermophila

Nowadays, biological databases are playing an increasingly critical role in biological research. Myceliophthora thermophila is an excellent thermophilic fungal chassis for industrial enzyme production and plant biomass-based chemical synthesis. The lack of a dedicated public database has made access to and reanalysis of M. thermophila data difficult. To bridge this gap, we developed MTD (https://mtd.biodesign.ac.cn/), a cloud-based omics database and interactive platform for M. thermophila. MTD integrates comprehensive genome annotations, sequence-based predictions, transcriptome data, curated experimental descriptions, and bioinformatics analysis tools, offering a comprehensive, one-stop solution with a 'top-down' search strategy to streamline M. thermophila research. The platform supports data reproduction, rapid querying, and in-depth mining of existing transcriptome datasets. Based on analyses using data and tools in MTD, we identified shifts in metabolic allocation in a glucoamylase hyperproduction strain of M. thermophila, highlighting changes in fatty acid biosynthesis and amino acids biosynthesis pathways, which provide new insights into the underlying phenotypic alterations. As a pioneering resource, MTD marks a key advancement in M. thermophila research and sets the model for developing similar databases for other species.

Structural dynamics of human fatty acid synthase in the condensing cycle

Long-chain fatty acids are the building blocks of fat in human bodies. In mammals, fatty acid synthase (FASN) contains multiple enzymatic domains to catalyse all chemical reactions needed for de novo fatty acid synthesis1. Although the chemical reactions carried out by these enzymatic domains are well defined, how the dimeric FASN with an open architecture continuously catalyses such reactions to synthesize a complete fatty acid remains elusive. Here, using a strategy of tagging and purifying endogenous FASN in HEK293T cells for single-particle cryo-electron microscopy studies, we characterized the structural dynamics of endogenous human FASN. We captured conformational snapshots of various functional substates in the condensing cycle and developed a procedure to analyse the particle distribution landscape of FASN with different orientations between its condensing and modifying wings. Together, our findings reveal that FASN function does not require a large rotational motion between its two main functional domains during the condensing cycle, and that the catalytic reactions in the condensing cycle carried out by the two monomers are unsynchronized. Our data thus provide a new composite view of FASN dynamics during the fatty acid synthesis condensing cycle.

Snapshots of acyl carrier protein shuttling in human fatty acid synthase

The mammalian fatty acid synthase (FASN) enzyme is a dynamic multienzyme that belongs to the megasynthase family. In mammals, a single gene encodes six catalytically active domains and a flexibly tethered acyl carrier protein (ACP) domain that shuttles intermediates between active sites for fatty acid biosynthesis1. FASN is an essential enzyme in mammalian development through the role that fatty acids have in membrane formation, energy storage, cell signalling and protein modifications. Thus, FASN is a promising target for treatment of a large variety of diseases including cancer, metabolic dysfunction-associated fatty liver disease, and viral and parasite infections2,3. The multi-faceted mechanism of FASN and the dynamic nature of the protein, in particular of the ACP, have made it challenging to understand at the molecular level. Here we report cryo-electron microscopy structures of human FASN in a multitude of conformational states with NADPH and NADP+ plus acetoacetyl-CoA present, including structures with the ACP stalled at the dehydratase (DH) and enoyl-reductase (ER) domains. We show that FASN activity in vitro and de novo lipogenesis in cells is inhibited by mutations at the ACP-DH and ACP-ER interfaces. Together, these studies provide new molecular insights into the dynamic nature of FASN and the ACP shuttling mechanism, with implications for developing improved FASN-targeted therapeutics.

Advancing time-resolved structural biology: latest strategies in cryo-EM and X-ray crystallography

Structural biology offers a window into the functionality of molecular machines in health and disease. A fundamental challenge lies in capturing both the high-resolution structural details and dynamic changes that are essential for function. The high-resolution methods of X-ray crystallography and electron cryo-microscopy (cryo-EM) are mainly used to study ensembles of static conformations but can also capture crucial dynamic transition states. Here, we review the latest strategies and advancements in time-resolved structural biology with a focus on capturing dynamic changes. We describe recent technology developments for time-resolved sample preparation and delivery in the cryo-EM and X-ray fields and explore how these technologies could mutually benefit each other to advance our understanding of biology at the molecular and atomic scales.

The structure of full-length AFPK supports the ACP linker in a role that regulates iterative polyketide and fatty acid assembly

The polyketide synthases (PKSs) in microbes and the cytoplasmic fatty acid synthases in humans (FASs) are related enzymes that have been well studied. As a result, there is a paradigm explaining in general terms how FASs repeatedly use a set of enzymatic domains to produce simple fats, while PKSs use the domains in a much more complex manner to produce pharmaceuticals and other elaborate molecules. However, most animals also have PKSs that do not conform to the rules described in microbes, including a large family of enzymes that bridge fatty acid and polyketide metabolism, the animal FAS-like PKSs (AFPKs). Here, we present the cryoelectron microscopy structures of two AFPKs from sea slugs. While the AFPK resemble mammalian FASs, their chemical products mimic those of PKSs in complexity. How then does the architecture of AFPKs facilitate this structural complexity? Unexpectedly, chemical complexity is controlled not solely by the enzymatic domains but is aided by the dynamics of the acyl carrier protein (ACP), a shuttle that moves intermediates between these domains. We observed interactions between enzyme domains and the linker-ACP domain, which, when manipulated, altered the kinetic properties of the enzyme to change the resulting chemical products. This unveils elaborate mechanisms and enzyme motions underlying lipid and polyketide biochemistry across the domains of life.

Deciphering the acidophilia and acid resistance in Acetilactobacillus jinshanensis dominating baijiu fermentation through multi-omics analysis

Lactic acid bacteria (LAB) are pivotal in constructing the intricate bio-catalytic networks underlying traditional fermented foods such as Baijiu. However, LAB and their metabolic mechanisms are partially understood in Moutai flavor Baijiu fermentation. Here, we found that Acetilactobacillus jinshanensis became the· dominant species with relative abundance reaching 92%, where the acid accumulated rapidly and peaked at almost 30 g/kg in Moutai flavor Baijiu. After separation, purification, and cultivation, A. jinshanensis exhibited pronounced acidophilia and higher acid resistance compared to other LAB. Further integrated multi-omics analysis revealed that fatty acid synthesis, cell membrane integrity, pHi and redox homeostasis maintenance, protein and amide syntheses were possibly crucial acid-resistant mechanisms in A. jinshanensis. Structural proteomics indicated that the surfaces of A. jinshanensis proteases contained more positively charged amino acid residues to maintain protein stability in acidic environments. The genes HSP20 and acpP were identified as acid-resistant genes for A. jinshanensis by heterologous expression analysis. These findings not only enhance our understanding of LAB in Baijiu, providing a scientific basis for acid regulation for production process, but also offer valuable insights for studying core species in other fermentation systems.

Synergistic photobiocatalysis for enantioselective triple-radical sorting

Multicomponent reactions-those where three or more substrates combine into a product-have been highly useful in rapidly building chemical building blocks of increased complexity1, but achieving this enzymatically has remained rare2-5. This limitation primarily arises because an enzyme's active site is not typically set up to address multiple substrates, especially in cases involving multiple radical intermediates6. Recently, chemical catalytic radical sorting has emerged as an enabling strategy for a variety of useful reactions7,8. However, making such processes enantioselective is highly challenging owing to the inherent difficulty in the stereochemical control of radicals9. Here we repurpose a thiamine-dependent enzyme10,11 through directed evolution and combine it with photoredox catalysis to achieve a photobiocatalytic enantioselective three-component radical cross-coupling. This approach combines three readily available starting materials-aldehydes, α-bromo-carbonyls and alkenes-to give access to enantioenriched ketone products. Mechanistic investigations provide insights into how this dual photocatalyst-enzyme system precisely directs the three distinct radicals involved in the transformation, unlocking enzyme reactivity. Our approach has achieved exceptional stereoselectivity, with 24 out of 33 examples achieving ≥97% enantiomeric excess.

Double-duty isomerases: a case study of isomerization-coupled enzymatic catalysis

Enzymes can usually be unambiguously assigned to one of seven classes specifying the basic chemistry of their catalyzed reactions. Less frequently, two or more reaction classes are catalyzed by a single enzyme within one active site. Two examples are an isomerohydrolase and an isomero-oxygenase that catalyze isomerization-coupled reactions crucial for production of vision-supporting 11-cis-retinoids. In these enzymes, isomerization is obligately paired and mechanistically intertwined with a second reaction class. A handful of other enzymes carrying out similarly coupled isomerization reactions have been described, some of which have been subjected to detailed structure-function analyses. Herein we review these rarefied enzymes, focusing on the mechanistic and structural basis of their reaction coupling with the goal of revealing catalytic commonalities.

Peripheral Linker Mediates Acyl Carrier Protein's Recognition of Dehydratase and Stabilizes Type-I Mycobacterium tuberculosis Fatty Acid Synthase

Incomplete structural details of Mycobacterium tuberculosis (Mtb) fatty acid synthase-I (FAS-I) at near-atomic resolution have limited our understanding of the shuttling mechanism of its mobile acyl carrier protein (ACP). Here, we have performed atomistic molecular dynamics simulation of Mtb FAS-I with a homology-modeled structure of ACP stalled at dehydratase (DH) and identified key residues that mediate anchoring of the recognition helix of ACP near DH. The observed distance between catalytic residues of ACP and DH agrees with that reported for fungal FAS-I. Further, the conformation of the peripheral linker is found to be crucial in stabilizing ACP near DH. Correlated interdomain motion is observed between DH, enoyl reductase, and malonyl/palmitoyl transferase, consistent with prior experimental reports of fungal and Mtb FAS-I.

Direct structural analysis of a single acyl carrier protein domain in fatty acid synthase from the fungus Saccharomyces cerevisiae

Acyl carrier protein (ACP) is the work horse of polyketide (PKS) and fatty acid synthases (FAS) and acts as a substrate shuttling domain in these mega enzymes. In fungi, FAS forms a 2.6 MDa symmetric assembly with six identical copies of FAS1 and FAS2 polypeptides. However, ACP spatial distribution is not restricted by symmetry owing to the long and flexible loops that tether the shuttling domain to its corresponding FAS2 polypeptide. This symmetry breaking has hampered experimental investigation of substrate shuttling route in fungal FAS. Here, we develop a protein engineering and expression method to isolate asymmetric fungal FAS proteins containing odd numbers of ACP domains. Electron cryomicroscopy (cryoEM) observation of the engineered complex reveals a non-uniform distribution of the substrate shuttling domain relative to its corresponding FAS2 polypeptide at 2.9 Å resolution. This work lays the methodological foundation for experimental study of ACP shuttling route in fungi.