Genomic analysis of siderophore β-hydroxylases reveals divergent stereocontrol and expands the condensation domain family.

Genome mining of biosynthetic pathways streamlines discovery of secondary metabolites but can leave ambiguities in the predicted structures, which must be rectified experimentally. Through coupling the reactivity predicted by biosynthetic gene clusters with verified structures, the origin of the β-hydroxyaspartic acid diastereomers in siderophores is reported herein. Two functional subtypes of nonheme Fe(II)/α-ketoglutarate-dependent aspartyl β-hydroxylases are identified in siderophore biosynthetic gene clusters, which differ in genomic organization-existing either as fused domains (IβH) at the carboxyl terminus of a nonribosomal peptide synthetase (NRPS) or as stand-alone enzymes (TβH)-and each directs opposite stereoselectivity of Asp β-hydroxylation.

Ambiguity of NRPS Structure Predictions: Four Bidentate Chelating Groups in the Siderophore Pacifibactin.

Identified through a bioinformatics approach, a nonribosomal peptide synthetase gene cluster in Alcanivorax pacificus encodes the biosynthesis of the new siderophore pacifibactin. The structure of pacifibactin differs markedly from the bioinformatic prediction and contains four bidentate metal chelation sites, atypical for siderophores. Genome mining and structural characterization of pacifibactin is reported herein, as well as characterization of pacifibactin variants accessible due to a lack of adenylation domain fidelity during biosynthesis.

β-Hydroxyaspartic acid in siderophores: biosynthesis and reactivity.

A growing number of siderophores are found to contain β-hydroxyaspartic acid (β-OH-Asp) as a functional group for Fe(III) coordination, along with the more common catechol and hydroxamic acid groups. This review covers the structures, biosynthesis, and reactions of peptidic β-OH-Asp siderophores. Hydroxylation of Asp in siderophore biosynthesis is predicted to be carried out either through discrete aspartyl β-hydroxylating enzymes or through hydroxylating domains within non-ribosomal peptide synthetases, both of which display sequence homology to known non-heme iron(II), α-ketoglutarate-dependent dioxygenases.

High interfacial activity of polymers "grafted through" functionalized iron oxide nanoparticle clusters.

The mechanism by which polymers, when grafted to inorganic nanoparticles, lower the interfacial tension at the oil-water interface is not well understood, despite the great interest in particle stabilized emulsions and foams. A simple and highly versatile free radical "grafting through" technique was used to bond high organic fractions (by weight) of poly(oligo(ethylene oxide) monomethyl ether methacrylate) onto iron oxide clusters, without the need for catalysts. In the resulting ∼1 μm hybrid particles, the inorganic cores and grafting architecture contribute to the high local concentration of grafted polymer chains to the dodecane/water interface to produce low interfacial tensions of only 0.