Metal Assimilation Pathways

Metal Assimilation Pathways
Chapter 7 Metal Assimilation Pathways Copyright © 2012 Elsevier Inc. All rights reserved.

Copyright © 2012 Elsevier Inc. All rights reserved.
FIGURE 7.1 World map showing the locations of the ten major iron addition experiments completed thus far. (Adapted from Vraspir & Butler, 2009.) Copyright © 2012 Elsevier Inc. All rights reserved.

FIGURE 7.2 Amphiphilic marine siderophores, including marinobactins, aquachelins, amphibactins, ochrobactins, and synechobactins. (Adapted from Vraspir & Butler, NIH Public Access.) Copyright © 2012 Elsevier Inc. All rights reserved.

FIGURE 7.3 Other marine siderophores, including alterobactins, pseudoalterobactins, aerobactin, petrobactins, and vibriobactins. (Adapted from Vraspir & Butler, NIH Public Access.) Copyright © 2012 Elsevier Inc. All rights reserved.

FIGURE 7.4 Proposed models depicting electron transfer pathways for Shewanella oneidensis MR-1 (a) and Geobacter sulfurreducens (b) during dissimilatory reduction of solid metal (hydr)oxides. (From Shi, Squier, Zachara & Fredrickson, 2007.) Copyright © 2012 Elsevier Inc. All rights reserved.

FIGURE 7.5 Schematic representation of iron uptake in Gram-negative bacteria. There are numerous iron uptake pathways in Gram-negative bacteria which include iron uptake from transferrin, siderophores, or haem. All of these uptake pathways require an outer-membrane receptor, a PBP, and an inner-membrane ABC transporter. Not all bacteria have all three systems; but some have more than one type. Transport through the outer-membrane receptor requires the action of the TonB system (TonB, ExbB, and ExbD). (From Krewulak & Vogel, Reproduced with permission from Elsevier.) Copyright © 2012 Elsevier Inc. All rights reserved.

FIGURE 7.6 Outer-membrane siderophore receptors from Escherichia coli and Pseudomonas aeruginosa. Ribbon representations of the (a) vitamin B12 (BtuB), (b) E. coli ferric-citrate (FecA), (c) ferric-enterobactin (FepA), (d) ferric-hydroxamate (FhuA), (e) P. aeruginosa pyochelin (FptA), and (f) P. aeruginosa pyoverdin (FpvA) receptors. The mixed  globular (cork) domain is coloured green while the 22-strand -barrel is coloured blue. (From Krewulak & Vogel, Reproduced with permission from Elsevier.) Copyright © 2012 Elsevier Inc. All rights reserved.

FIGURE 7.7 Ribbon representations of the crystal structures of (a) ligand-free and (b) FecA bound to ferric citrate. The 22- strand barrel is depicted in ribbon format and the N-terminal cork domain is in space-filling format. The binding of ferric citrate (coloured orange) induces a conformational change in the extracellular loops L7 (cyan) and L8 (red) such that the solvent accessibility of ferric citrate is reduced. (From Krewulak & Vogel, Reproduced with permission from Elsevier.) Copyright © 2012 Elsevier Inc. All rights reserved.

FIGURE 7.8 A representation of the siderophore uptake pathway in E. coli using ferric-enterobactin (FeEnt) transport as an example (see text for details). (From Chu et al., Reproduced with permission from Springer.) Copyright © 2012 Elsevier Inc. All rights reserved.

FIGURE 7.9 Schematic representation of iron uptake in Gram-positive bacteria, which unlike Gram-negative bacteria, lack an outer membrane. Therefore, the uptake of iron from haem, siderophore, or transferrin involves a membrane-anchored binding protein and a membrane-associated ABC transporter. (From Krewulak & Vogel, Reproduced with permission from Elsevier.) Copyright © 2012 Elsevier Inc. All rights reserved.

FIGURE 7.11 Structure of Cu-methanobactin from M. trichosporium. (a) Schematic diagram. (b) Ball-and-stick representation of crystal structure. The copper ion is shown as a brown sphere. (From Balasubramanian & Rosenzweig, Copyright 2008, American Chemical Society.) Copyright © 2012 Elsevier Inc. All rights reserved.

FIGURE 7.12 Iron uptake systems of S. cerevisiae. The FIT mannoproteins of the cell wall facilitate retention of siderophoreiron in the cell wall, but are not required for siderophore uptake. Many siderophores likely cross the cell wall through non-specific pores. Siderophore-bound iron can be reduced and released from the siderophore by the FRE reductases. Ferric iron salts and low-affinity chelates are also reduced by the FRE reductases prior to uptake. Reduced iron can then be taken up through either the high-affinity ferrous iron transporter (the FET3 and FTR1 complex) or through low-affinity transporters (FET4 and SMF1). FET3 acquires copper intracellularly through the activities of the copper chaperone ATX1 and the copper transporter CCC2. Intact siderophoreiron chelates can be taken up via members of the ARN transporter family. The ARN transporter binds the ferric siderophore, and the transportersiderophore complex undergoes endocytosis prior to translocation of the ferric siderophore chelate across the membrane. (From Philpott, Copyright 2006, with permission from Elsevier.) Copyright © 2012 Elsevier Inc. All rights reserved.

FIGURE 7.13 Cartoon representing the effect of iron chelators in dissociative and channeling models of transfer of Fe(III) from Fet3p to Ftr1p. (Adapted from Kwok et al., 2006.) Copyright © 2012 Elsevier Inc. All rights reserved.

FIGURE 7.14 Mechanisms of iron uptake by higher plants. In strategy I plants (e.g., Arabidopsis, pea and tomato), Fe(III) chelates are reduced before the Fe(II) ion is transported across the plasma membrane. Strategy II plants (e.g., barley, maize, and rice) release siderophores capable of solubilising external Fe(III) and then transport the Fe(III) siderophore complex into the cell. AHA2 is a P-type H+-ATPase, FRO2 is the Fe(III) chelate reductase, IRT1 is a Fe(II) transporter, and YS1 is the transporter of the phytosiderophore (PS)Fe complex. (Adapted from Schmidt, Copyright 2003, with permission from Elsevier.) Copyright © 2012 Elsevier Inc. All rights reserved.

FIGURE 7.15 (a) Outline of biosynthesis of nicotianamine in graminaceous and non-graminaceous plants and its conversion to deoxymugineic acid (DMA) in graminaceous plants. (b) Conversion of DMA to other phytosiderophores. Copyright © 2012 Elsevier Inc. All rights reserved.

FIGURE 7.16 Predicted membrane topologies for the ZIP/SLC39 and CDF/Znt/SLC30 families of metal ion transporters (a) ZIP/SLC39 (b) CDF/Znt/SLC30. (From Eide, Copyright 2006 with permission from Elsevier.) Copyright © 2012 Elsevier Inc. All rights reserved.

FIGURE 7.17 Schematic representation of iron absorption in normal subjects. Iron is taken up from the gastrointestinal tract either as haem or non-haem iron. The former is degraded to release Fe(II) by haem oxygenase, whereas the latter is reduced by DcytB and transported across the apical membrane by DCT-1.Within the enterocyte, the iron pool can equilibrate with the intracellular storage protein ferritin. At the basolateral membrane, iron is transported out of the cell by IREG-1; its incorporation into apotransferrin may be aided by the ferroxidase activity of hephaestin. Dcytb, Duodenal cytochrome b; DCT1, divalent cation transporter protein 1; IREG-1, iron-regulated transporter-1; Haem ox, haem oxygenase; Cp, ceruloplasmin; Tf, transferrin; NTBI, non-transferrin-bound iron. Copyright © 2012 Elsevier Inc. All rights reserved.

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