Biology Reference
In-Depth Information
Figure 3.4
Iron uptake pathway in
Anabaena
sp. PCC 7120. See the colour plate.
Siderophore uptake was extensively studied in
E. coli
and
Pseudomonas
aeruginosa
(
Faraldo-Gómez & Sansom, 2003
). It was demonstrated that sid-
erophores bind with high affinity to specific transporters in the outer mem-
brane of Gram-negative bacteria (TonB-dependant transporters, TBDTs).
Despite the substrate diversity of TBDTs, the structure of these transporters
seems to be similar consisting of a 22-stranded β-barrel embedded in the
membrane and an N-terminal plug domain that is located within the bar-
rel (
Fig. 3.5
). Among TBDT sequences of different species, the majority of
identity is in the plug domain, whereas the β-barrel is poorly conserved
in sequence. TBDT substrates bind, primarily, to the extracellular pocket
of the transporter consisting of substrate-binding sites, composed of the
plug and the barrel domain. In most cases, these substrate-binding sites lack
sequence conservation (
Chimento, Kadner, & Wiener, 2005
) indicating the
specificity of the transporters for different substrates. These include, beside
