stages (Djoko et al. 2010). Type 1 (T1), type 2 (T2) and two type 3 (T3), three
different kinds of copper atoms, are present in multicopper oxidases. Of them, T1 is
in the protein’s interior and oxidizes the substrate, while T2 and two T3 make a
trinuclear centre (TNC) where reduction of dioxygen takes place. But, there is an
additional methionine-rich helix in cueO which inhibits the solvent access to the T1
position and makes an extra copper-binding location for storage of copper (Singh
et al. 2004). An additional regulatory gene CsoR with Cu
+ inhibits repression of
copper tolerance genes (Chang et al. 2014). It was observed that copper transport
operon copYAZ is present in a Streptococcus strain which has the heavy metalbinding proteins named copY and copZ (Vats and Lee 2001). Pseudomonas
fluorescens possess copRSCD operon (Hu et al. 2009), while opposite to this,
Helicobacter pylori possess two different operons hpcopA and hpcopP to export
and import copper (Ge and Taylor 1996). One more copper regulatory system is
present in B. subtilis which is mediated through YcnJ and controlled by YcnK and
CsoR (Chillappagari et al. 2009). These genes collectively maintain copper
homoeostasis inside the cell. But, the primary method to remove cytoplasmic is an
ATPase-driven copper efflux system. Periplasmic copper management, multicopper
oxidases, metallochaperones and RND systems are implicated in this mechanism
(Bondarczuk and Piotrowska-Seget 2013). According to Grass et al. (2004), in
E. coli, not only multicopper oxidase cueO is induced in the company of copper to
oxidize Cu(I) in the form of Cu(II) in the periplasm, but also enterobactin, a
catecholate consisting ligands, is also produced. Like siderophore, enetrobactin
has capability to reduce Cu(II), and it was anticipated that enterobactin oxidation
through CueO has an accompanying role in Cu tolerance by not producing highly
toxic Cu(I) ions. Furthermore, one intermediate of enterobactin biosynthesis,
2,3-dihydroxybenzoic acid (DHB), strongly combines with Cu ions, behaving like
a Cu sink. Additionally, yersiniabactin of uropathogenic E. coli sequester Cu
(II) outside bacterial cells protects the bacteria from intracellular killing and inhibits
its catechol-mediated reduction in the form of Cu(I) (Chaturvedi et al. 2012).
Moreover, the Cu(II)–yersiniabactin complex possesses superoxide dismutase activity to safeguard bacteria by oxidative stress inside phagocytic vesicles (Chaturvedi
et al. 2014).
12.7.3 Lead
Lead (Pb) is a very harmful, unrelating and non-essential metal pollutant. Many
bacteria like Arthrobacter spp., B. megaterium, P. marginalis, Citrobacter freundii,
S. aureus, and E. coli are lead tolerant. Endogeneous pMOL30 megaplasmid present
in the bacterium Cupriavidus (Ralstonia) metallidurans CH34 is probably one of the
most investigated lead resistance operons (Borremans et al. 2001). This pbr operon
has several structural genes as well as one regulatory gene (pbrR). Of these, pbrT
gene is coding for Pb(II) uptake protein, pbrA is coding for P-type Pb(II) efflux
ATPase, and pbrB is coding for expected integral membrane protein whose role is
not known, while pbrC is coding for expected prolipoprotein signal peptidase. It was
336
N. Srivastava
different kinds of copper atoms, are present in multicopper oxidases. Of them, T1 is
in the protein’s interior and oxidizes the substrate, while T2 and two T3 make a
trinuclear centre (TNC) where reduction of dioxygen takes place. But, there is an
additional methionine-rich helix in cueO which inhibits the solvent access to the T1
position and makes an extra copper-binding location for storage of copper (Singh
et al. 2004). An additional regulatory gene CsoR with Cu
+ inhibits repression of
copper tolerance genes (Chang et al. 2014). It was observed that copper transport
operon copYAZ is present in a Streptococcus strain which has the heavy metalbinding proteins named copY and copZ (Vats and Lee 2001). Pseudomonas
fluorescens possess copRSCD operon (Hu et al. 2009), while opposite to this,
Helicobacter pylori possess two different operons hpcopA and hpcopP to export
and import copper (Ge and Taylor 1996). One more copper regulatory system is
present in B. subtilis which is mediated through YcnJ and controlled by YcnK and
CsoR (Chillappagari et al. 2009). These genes collectively maintain copper
homoeostasis inside the cell. But, the primary method to remove cytoplasmic is an
ATPase-driven copper efflux system. Periplasmic copper management, multicopper
oxidases, metallochaperones and RND systems are implicated in this mechanism
(Bondarczuk and Piotrowska-Seget 2013). According to Grass et al. (2004), in
E. coli, not only multicopper oxidase cueO is induced in the company of copper to
oxidize Cu(I) in the form of Cu(II) in the periplasm, but also enterobactin, a
catecholate consisting ligands, is also produced. Like siderophore, enetrobactin
has capability to reduce Cu(II), and it was anticipated that enterobactin oxidation
through CueO has an accompanying role in Cu tolerance by not producing highly
toxic Cu(I) ions. Furthermore, one intermediate of enterobactin biosynthesis,
2,3-dihydroxybenzoic acid (DHB), strongly combines with Cu ions, behaving like
a Cu sink. Additionally, yersiniabactin of uropathogenic E. coli sequester Cu
(II) outside bacterial cells protects the bacteria from intracellular killing and inhibits
its catechol-mediated reduction in the form of Cu(I) (Chaturvedi et al. 2012).
Moreover, the Cu(II)–yersiniabactin complex possesses superoxide dismutase activity to safeguard bacteria by oxidative stress inside phagocytic vesicles (Chaturvedi
et al. 2014).
12.7.3 Lead
Lead (Pb) is a very harmful, unrelating and non-essential metal pollutant. Many
bacteria like Arthrobacter spp., B. megaterium, P. marginalis, Citrobacter freundii,
S. aureus, and E. coli are lead tolerant. Endogeneous pMOL30 megaplasmid present
in the bacterium Cupriavidus (Ralstonia) metallidurans CH34 is probably one of the
most investigated lead resistance operons (Borremans et al. 2001). This pbr operon
has several structural genes as well as one regulatory gene (pbrR). Of these, pbrT
gene is coding for Pb(II) uptake protein, pbrA is coding for P-type Pb(II) efflux
ATPase, and pbrB is coding for expected integral membrane protein whose role is
not known, while pbrC is coding for expected prolipoprotein signal peptidase. It was
336
N. Srivastava