Understanding the role of histidine in the GHSxG acyltransferase active site motif: evidence for histidine stabilization of the malonyl-enzyme intermediate

Mixed alkyl/aryl phosphonates identify metabolic serine hydrolases as antimalarial targets

Malaria, caused by Plasmodium falciparum, remains a significant health burden. One major barrier for developing antimalarial drugs is the ability of the parasite to rapidly generate resistance. We previously demonstrated that salinipostin A (SalA), a natural product, potently kills parasites by inhibiting multiple lipid metabolizing serine hydrolases, a mechanism that results in a low propensity for resistance. Given the difficulty of employing natural products as therapeutic agents, we synthesized a small library of lipidic mixed alkyl/aryl phosphonates as bioisosteres of SalA. Two constitutional isomers exhibited divergent antiparasitic potencies that enabled the identification of therapeutically relevant targets. The active compound kills parasites through a mechanism that is distinct from both SalA and the pan-lipase inhibitor orlistat and shows synergistic killing with orlistat. Our compound induces only weak resistance, attributable to mutations in a single protein involved in multidrug resistance. These data suggest that mixed alkyl/aryl phosphonates are promising, synthetically tractable antimalarials.

Mixed Alkyl/Aryl Phosphonates Identify Metabolic Serine Hydrolases as Antimalarial Targets

Malaria, caused by Plasmodium falciparum, remains a significant health burden. A barrier for developing anti-malarial drugs is the ability of the parasite to rapidly generate resistance. We demonstrated that Salinipostin A (SalA), a natural product, kills parasites by inhibiting multiple lipid metabolizing serine hydrolases, a mechanism with a low propensity for resistance. Given the difficulty of employing natural products as therapeutic agents, we synthesized a library of lipidic mixed alkyl/aryl phosphonates as bioisosteres of SalA. Two constitutional isomers exhibited divergent anti-parasitic potencies which enabled identification of therapeutically relevant targets. We also confirm that this compound kills parasites through a mechanism that is distinct from both SalA and the pan-lipase inhibitor, Orlistat. Like SalA, our compound induces only weak resistance, attributable to mutations in a single protein involved in multidrug resistance. These data suggest that mixed alkyl/aryl phosphonates are a promising, synthetically tractable anti-malarials with a low-propensity to induce resistance.

Three-in-one: Miniature Models of Natural Acyl-transfer Systems Enable Vector-selective Reaction on the Primary Side of Cyclodextrins

Miniature models of acyl-transfer systems in cells, which were composed by replacing the protein, coenzyme and substrate with CD, functional group, and CD, respectively, and combining them all together in one, displayed definite role-sharing and exact cooperation of the functional groups and hydrophobic cavity, and thus enabled the regio-specific reaction.

Computational studies on the substrate specificity of an acyltransferase domain from salinomycin polyketide synthase

The complex of SalAT14 and its cognate substrate EMCoA is apt to stay in a conformation suitable for the reaction. Computational investigations reveal the structural basis of AT specificity and could potentially help the engineering of modular PKSs.

Structural and Biochemical Insight into the Recruitment of Acyl Carrier Protein-Linked Extender Units in Ansamitocin Biosynthesis

A few acyltransferase (AT) domains of modular polyketide synthases (PKSs) recruit acyl carrier protein (ACP)-linked extender units with unusual C2 substituents to confer functionalities that are not available in coenzyme A (CoA)-linked ones. In this study, an AT specific for methoxymalonyl (MOM)-ACP in the third module of the ansamitocin PKS was structurally and biochemically characterized. The AT uses a conserved tryptophan residue at the entrance of the substrate binding tunnel to discriminate between different carriers. A W275R mutation switches its carrier specificity from the ACP to the CoA molecule. The acyl-AT complex structures clearly show that the MOM-ACP accepted by the AT has the 2S instead of the opposite 2R stereochemistry that is predicted according to the biosynthetic derivation from a d-glycolytic intermediate. Together, these results reveal the structural basis of ATs recognizing ACP-linked extender units in polyketide biosynthesis.

Control Mechanism for cis Double-Bond Formation by Polyunsaturated Fatty-Acid Synthases

Polyunsaturated fatty acids (PUFAs) such as docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and arachidonic acid (ARA) are essential fatty acids for humans. Some microorganisms biosynthesize these PUFAs through PUFA synthases composed of four subunits with multiple catalytic domains. These PUFA synthases each create a specific PUFA without undesirable byproducts, even though the multiple catalytic domains in each large subunit are very similar. However, the detailed biosynthetic pathways and mechanisms for controlling final-product profiles are still obscure. In this study, the FabA-type dehydratase domain (DH_FabA ) in the C-subunit and the polyketide synthase-type dehydratase domain (DH_PKS ) in the B-subunit of ARA synthase were revealed to be essential for ARA biosynthesis by in vivo gene exchange assays. Furthermore, in vitro analysis with truncated recombinant enzymes and C₄ - to C₈ -acyl ACP substrates showed that ARA and EPA synthases utilized two types of DH domains, DH_PKS and DH_FabA , depending on the carbon-chain length, to introduce either saturation or cis double bonds to growing acyl chains.

Loading of malonyl-CoA onto tandem acyl carrier protein domains of polyunsaturated fatty acid synthases

Omega-3 polyunsaturated fatty acids (PUFA) are produced in some unicellular organisms, such as marine gammaproteobacteria, myxobacteria, and thraustochytrids, by large enzyme complexes called PUFA synthases. These enzymatic complexes resemble bacterial antibiotic-producing proteins known as polyketide synthases (PKS). One of the PUFA synthase subunits is a conserved large protein (PfaA in marine proteobacteria) that contains three to nine tandem acyl carrier protein (ACP) domains as well as condensation and modification domains. In this work, a study of the PfaA architecture and its ability to initiate the synthesis by selecting malonyl units has been carried out. As a result, we have observed a self-acylation ability in tandem ACPs whose biochemical mechanism differ from the previously described for type II PKS. The acyltransferase domain of PfaA showed a high selectivity for malonyl-CoA that efficiently loads onto the ACPs domains. These results, together with the structural organization predicted for PfaA, suggest that this protein plays a key role at early stages of the anaerobic pathway of PUFA synthesis.