Assimilation in Fungi and Plants

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, 2008. Copyright 2008, American Chemical Society.) 

Responsible for a large number of oral and vaginal mucosal infections, as well as systemic infections, particularly when cellular immunity is compromised. 

The high-affinity pathway involves oxidation of Fe to Fe by the ferroxidase FET3 and subsequent transport of Fe across the plasma membrane by the permease FTRl. FET3p is a member of the family of multicopper oxidases, which include ascorbate oxidase, laccase, and ceruloplasmin (see Chapter 14), and does not become functional until it is loaded with copper intracellularly through the activities of the copper chaperone ATX Ip and the copper transporter CCC2p. It appears that Fe produced by FET3 is transferred directly to FTRl, and does not equilibrate with the bulk phase, as is illustrated in Fig. 7.13. This is almost certainly achieved by the classic metabolite-channeling mechanism, a common feature of multifunctional enzymes. 

FIGURE 7.13 Cartoon representing the effect of iron chelators in dissociative and channeling models of transfer of Fe(III) from Fet3p to Ftrlp. (Adapted from Kwok et al, 2006.) 

In common with most prokaryotes, many fungi have siderophore-dependent iron uptake systems. The ferri-chrome-type siderophores are often employed, although other types of siderophore are also used. Indeed, even if, like the quintessential scavenger baker s yeast (Saccharomyces cerevisiae), they produce no siderophores of their own, they nonetheless have several distinct facilitators for the uptake of ferric siderophores, including ferric enterobactin, which is produced by many bacteria, but not by fungi. 

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