Chemistry Reference
In-Depth Information
(a)
(b)
FIGURE 8.3
Interaction of Fur family proteins with DNA and metal ions. (a) Model of the interaction of Fur
PA
with DNA. The N-terminal
DNA-binding domains are in red and blue, with the C-terminal dimerisation domains in green. The classical Fur box is defined as a 19-bp
inverted repeat sequence (capitals), originally assumed to bind one dimer. (b) Comparison of proposed metal-binding sites in Fur
PA
and PerR
BS
.
(From
Lee & Helmann, 2007
.
Reproduced with permission from Springer.)
switching off ryhB as well, iron storage genes are switched on. Conversely, in iron penury, inactive Fur allows the
genes for iron acquisition to be switched on, and those for iron storage to be switched off. We will see later in the
chapter that a similar up- and downregulation of iron uptake and storage pathways, albeit at the level of translation
rather than transcription, operates in animals.
2.
Copper and Zinc
Both copper and zinc appear to be stored in many bacteria in cysteine-rich proteins, called metallothioneins, which
will be discussed from a structural point of view later in the chapter. The expression of these metal-sequestering,
low-molecular-weight, cysteine-rich proteins, is often induced by both monovalent Cu(I) and divalent Zn(II), as
well as by the non-biologically necessary, but potentially toxic, Ag(I) and Cd(II).
Because of their importance in the activity of many enzymes, bacteria have had to develop efficient uptake
systems for copper and zinc. However, since both of these metals are toxic in excess, their intracellular content
must be tightly regulated. Copper uptake homeostasis has been most extensively studied in the Gram-positive
