naphthoquinones and 1-4-dihydroxy-2-naphthoic-acid

Some anaerobic bacteria use insoluble minerals as terminal electron acceptors and discovering the ways in which electrons move through the membrane barrier to the exterior acceptor forms an active field of research with implications for both bacterial physiology and bioenergy. A previous study suggested that

Topics: Anaerobiosis; Electron Transport; Naphthols; Naphthoquinones; Oxidation-Reduction; Shewanella

The synthesis of phylloquinone (vitamin K1) in photosynthetic organisms requires a thioesterase that hydrolyzes 1,4-dihydroxy-2-naphthoyl-CoA (DHNA-CoA) to release 1,4-dihydroxy-2-naphthoate (DHNA). Cyanobacteria and plants contain distantly related hotdog-fold thioesterases that catalyze this reaction, although the structural basis of these convergent enzymatic activities is unknown. To investigate this, the crystal structures of hotdog-fold DHNA-CoA thioesterases from the cyanobacterium Synechocystis (Slr0204) and the flowering plant Arabidopsis thaliana (AtDHNAT1) were determined. These enzymes form distinct homotetramers and use different active sites to catalyze hydrolysis of DHNA-CoA, similar to the 4-hydroxybenzoyl-CoA (4-HBA-CoA) thioesterases from Pseudomonas and Arthrobacter. Like the 4-HBA-CoA thioesterases, the DHNA-CoA thioesterases contain either an active-site aspartate (Slr0204) or glutamate (AtDHNAT1) that are predicted to be catalytically important. Computational modeling of the substrate-bound forms of both enzymes indicates the residues that are likely to be involved in substrate binding and catalysis. Both enzymes are selective for DHNA-CoA as a substrate, but this selectivity is achieved using divergent predicted binding strategies. The Slr0204 binding pocket is predominantly hydrophobic and closely conforms to DHNA, while that of AtDHNAT1 is more polar and solvent-exposed. Considered in light of the related 4-HBA-CoA thioesterases, these structures indicate that hotdog-fold thioesterases using either an active-site aspartate or glutamate diverged into distinct clades prior to the evolution of strong substrate specificity in these enzymes.

Topics: Arabidopsis; Aspartic Acid; Catalytic Domain; Crystallography, X-Ray; Glutamic Acid; Hydro-Lyases; Naphthols; Naphthoquinones; Protein Binding; Protein Folding; Protein Multimerization; Synechocystis; Thiolester Hydrolases; Vitamin K 1

Phylloquinone (vitamin K(1)) is a bipartite molecule that consists of a naphthoquinone ring attached to a phytyl side chain. The coupling of these 2 moieties depends on the hydrolysis of the CoA thioester of 1,4-dihydroxy-2-naphthoate (DHNA), which forms the naphthalenoid backbone. It is not known whether such a hydrolysis is enzymatic or chemical. In this study, comparative genomic analyses identified orthologous genes of unknown function that in most species of cyanobacteria cluster with predicted phylloquinone biosynthetic genes. The encoded approximately 16-kDa proteins display homology with some Hotdog domain-containing CoA thioesterases that are involved in the catabolism of 4-hydroxybenzoyl-CoA and gentisyl-CoA (2,5-dihydroxybenzoyl-CoA) in certain soil-dwelling bacteria. The Synechocystis ortholog, encoded by gene slr0204, was expressed as a recombinant protein and was found to form DHNA as reaction product. Unlike its homologs in the Hotdog domain family, Slr0204 showed strict substrate specificity. The Synechocystis slr0204 knockout was devoid of DHNA-CoA thioesterease activity and accumulated DHNA-CoA. As a result, knockout cells contained 13-fold less phylloquinone than their wild-type counterparts and displayed the typical photosensitivity to high light associated to phylloquinone deficiency in cyanobacteria.

Topics: Cyanobacteria; Hydrolysis; Metabolic Networks and Pathways; Mutation; Naphthols; Naphthoquinones; Substrate Specificity; Thiolester Hydrolases; Vitamin K 1

The incorporation of [1-(13)C]glucose into 2,3-epoxysesamone, the main prenylnaphthoquinone in a hairy root culture of Sesamum indicum, indicated that the naphthoquinone moiety and dimethylallyl group were respectively derived from o-succinylbenzoate produced through a shikimate pathway and non-mevalonate pathway. The labeling pattern also demonstrated that prenylation occurred at C-2 in 1,4-dihydroxy-2-naphthoate.

Topics: Culture Techniques; Epoxy Compounds; Naphthols; Naphthoquinones; Prenylation; Sesamum; Shikimic Acid

Topics: Bacillus subtilis; Bacteria; Chromates; Coenzyme A; Escherichia coli; Genes, Bacterial; Humans; Mutation; Naphthols; Naphthoquinones; Phenylbutyrates; Pyruvates; Pyruvic Acid; Shikimic Acid; Vitamin K