Title

Molecular Characterization of Staphyloferrin B Biosynthesis in Staphylococcus aureus

Document Type

Article

Publication Date

11-2009

Journal

Molecular Microbiology

Volume

74

Issue

3

First Page

594

Last Page

608

URL with Digital Object Identifier

10.1111/j.1365-2958.2009.06880.x

Abstract

Siderophores are iron-scavenging molecules produced by many microbes. In general, they are synthesized using either non-ribosomal peptide synthetase (NRPS) or NRPS-independent siderophore (NIS) pathways. Staphylococcus aureus produces siderophores, of which the structures of staphyloferrin A and staphyloferrin B are known. Recently, the NIS biosynthetic pathway for staphyloferrin A was characterized. Here we show that, in S. aureus, the previously identified sbn (siderophore biosynthesis) locus encodes enzymes required for the synthesis of staphyloferrin B, an alpha-hydroxycarboxylate siderophore comprised of l-2,3-diaminopropionic acid, citric acid, 1,2-diaminoethane and alpha-ketoglutaric acid. Staphyloferrin B NIS biosynthesis was recapitulated in vitro, using purified recombinant Sbn enzymes and the component substrates. In vitro synthesized staphyloferrin B readily promoted the growth of iron-starved S. aureus, via the ABC transporter SirABC. The SbnCEF synthetases and a decarboxylase, SbnH, were necessary and sufficient to produce staphyloferrin B in reactions containing component substrates l-2,3-diaminopropionic acid, citric acid and alpha-ketoglutaric acid. Since 1,2-diaminoethane was not required, this component of the siderophore arises from the SbnH-dependent decarboxylation of a 2,3-diaminoproprionic acid-containing intermediate. Liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) analyses of a series of enzyme reactions identified mass ions corresponding to biosynthetic intermediates, allowing for the first proposed biosynthetic pathway for staphyloferrin B.