The dhb operon of Bacillus subtilis encodes the biosynthetic template for the catecholic siderophore 2,3-dihydroxybenzoate-glycine-threonine trimericester bacillibactin
Jj. May et al., The dhb operon of Bacillus subtilis encodes the biosynthetic template for the catecholic siderophore 2,3-dihydroxybenzoate-glycine-threonine trimericester bacillibactin, J BIOL CHEM, 276(10), 2001, pp. 7209-7217
Bacillus subtilis was reported to produce the catecholic siderophore itoic
acid (2,3-dihydroxybenzoate (DHB)-glycine) in response to iron deprivation,
However, by inspecting the DNA sequences of the genes dhbE, dhbB, and dhbF
as annotated by the B, subtilis genome project to encode the synthetase co
mplex for the siderophore assembly, various sequence errors within the dhbF
gene were predicted and confirmed by re-sequencing. According to the corre
cted sequence, dhbF encodes a dimodular instead of a monomodular nonribosom
al peptide synthetase, We have heterologously expressed, purified, and assa
yed the substrate selectivity of the recombinant proteins DhbB, DhbE, and D
hbF, DhbE, a stand-alone adenylation domain of 59.9 kDa, activates, in an A
TP-dependent reaction, I)HB, which is subsequently transferred to the free
thiol group of the cofactor phosphopantetheine of the bifunctional isochori
smate lyase/aryl carrier protein DhbB, The third synthetase, DhbF, is a dim
odular nonribosomal peptide synthetase of 264 kDa that specifically adenyla
tes threonine and, to a lesser extent, glycine and that covalently loads bo
th amino acids onto their corresponding peptidyl carrier domains. To functi
onally link the dhb gene cluster to siderophore synthesis, we have disrupte
d the dhbF gene. Comparative mass spectrometric analysis of culture extract
s from both the wild type and the dhbF mutant led to the identification of
a mass peak at mit 881 ([M-H](1-)) that corresponds to a cyclic trimeric es
ter of DHB-glycine-threonine.