Glutathione (GSH)
All living beings have glutathione (GSH), L-glutamyl-L-cysteinyl-glycine, an antioxidant which is soluble as well as highly significant non-protein thiol. Although it
has (Glu-Cys-Gly) amino acids, its biochemical features are due to a cysteine thiol
group which is found in its active site (Bae and Mehra 1997; Penninckx 2000, 2002;
Mendoza-Cózatl et al. 2005). The GSH regulates its own synthesis and takes part in
different mechanisms such as it regulates intracellular redox state, inactivates ROS,
transfers GSH linked amino acid as well as other molecules and builds up sulphur
and cysteine. In mammals, it is present in liver at higher levels and has same
biosynthesis in plants, yeast and protists. The mitochondria and the nucleus are
not damaged by the action of ROS because of their own GSH reservation which is
critical or helpful in protecting these structures (Penninckx 2002; Inouhe 2005;
Mendoza-Cózatl et al. 2005). In yeast, the cell defence system against Cd
2+ toxicity
works through the making of a GSH-Cd
2+ complex which reduces the lipid peroxidation of the cell membrane and permits the transfer of GSH-Cd
2+ conjugate inside
the vacuole. This causes reduction in the levels of toxic metals of cytosol which
ultimately assists in decreasing oxidative stress (Penninckx 2000; Adamis et al.
2004; Kobayashi et al. 2006; Preveral et al. 2006).
Natural Phytochelatins (PCs) and Synthetic Phytochelatin (EC20)
Some small peptides rich in cysteine with general structure (Glu-Cys) nGly
(n ¼ 2–11) are known as phytochelatins (Grill et al. 1985; Cobbett 2000). PC
synthase catalyzes glutathione (GSH) in different stages to produce PCs (Grill
et al. 1985; Gupta et al. 2005). Because of them, ions become capable of ligating
heavy metal ions by their thiol as well as carboxyl residues (Kobayashi et al. 2006;
Inouhe 2005). Plants, fungi, nematodes, parasites and algae along with
cyanobacteria possess PCs. These PCs have better capability to bind heavy metal
ions (1 atom per cysteine) in comparison to MTs, although they have been placed
under MT-III class. The initial efforts of inducing recombinant PCs E.coli strongly
opposed by type γ chemical bonds formed between Glu-Cys units as a result of
multienzyme mechanisms. Type α bonds found in amino acid chains of all proteins
are not like these bindings (Bae et al. 2001; Cobbett 2000; Penninckx 2000; Gupta
et al. 2005; Inouhe 2005; Hirata et al. 2005; Mendoza-Cózatl et al. 2005; Wu et al.
2006). Another option to this was to produce an in vitro gene which encodes proteins
analogous to PCs with the structure (Glu-Cys) nGly (ECs) in which all amino acids
are chemically linked through type α. Therefore, 20 units of Glu-Cys (EC) repeats
are present in the synthetic phytochelatin EC20 which has higher capability to bind
heavy metal ions in comparison to natural PCs. Production of recombinant bacterial
strains is a routine process now (Bae et al. 2000, 2001; Xu et al. 2002; Lee et al.
2002; Wu et al. 2006), but not much work is done in yeast (Schmitt et al. 2006).
Induction of EC20 can be referred to identify microorganisms with better capability
to bind heavy metal ions to use in bioremediation. MTS, PCs and ECs along with
other genetic engineering approaches have been searched to produce new recombinant microbial strains for getting these proteins to stay attached to the external
surface cell (“cell-surface display”) (Deng et al. 2003; Merle et al. 2003; Kim
330
N. Srivastava
All living beings have glutathione (GSH), L-glutamyl-L-cysteinyl-glycine, an antioxidant which is soluble as well as highly significant non-protein thiol. Although it
has (Glu-Cys-Gly) amino acids, its biochemical features are due to a cysteine thiol
group which is found in its active site (Bae and Mehra 1997; Penninckx 2000, 2002;
Mendoza-Cózatl et al. 2005). The GSH regulates its own synthesis and takes part in
different mechanisms such as it regulates intracellular redox state, inactivates ROS,
transfers GSH linked amino acid as well as other molecules and builds up sulphur
and cysteine. In mammals, it is present in liver at higher levels and has same
biosynthesis in plants, yeast and protists. The mitochondria and the nucleus are
not damaged by the action of ROS because of their own GSH reservation which is
critical or helpful in protecting these structures (Penninckx 2002; Inouhe 2005;
Mendoza-Cózatl et al. 2005). In yeast, the cell defence system against Cd
2+ toxicity
works through the making of a GSH-Cd
2+ complex which reduces the lipid peroxidation of the cell membrane and permits the transfer of GSH-Cd
2+ conjugate inside
the vacuole. This causes reduction in the levels of toxic metals of cytosol which
ultimately assists in decreasing oxidative stress (Penninckx 2000; Adamis et al.
2004; Kobayashi et al. 2006; Preveral et al. 2006).
Natural Phytochelatins (PCs) and Synthetic Phytochelatin (EC20)
Some small peptides rich in cysteine with general structure (Glu-Cys) nGly
(n ¼ 2–11) are known as phytochelatins (Grill et al. 1985; Cobbett 2000). PC
synthase catalyzes glutathione (GSH) in different stages to produce PCs (Grill
et al. 1985; Gupta et al. 2005). Because of them, ions become capable of ligating
heavy metal ions by their thiol as well as carboxyl residues (Kobayashi et al. 2006;
Inouhe 2005). Plants, fungi, nematodes, parasites and algae along with
cyanobacteria possess PCs. These PCs have better capability to bind heavy metal
ions (1 atom per cysteine) in comparison to MTs, although they have been placed
under MT-III class. The initial efforts of inducing recombinant PCs E.coli strongly
opposed by type γ chemical bonds formed between Glu-Cys units as a result of
multienzyme mechanisms. Type α bonds found in amino acid chains of all proteins
are not like these bindings (Bae et al. 2001; Cobbett 2000; Penninckx 2000; Gupta
et al. 2005; Inouhe 2005; Hirata et al. 2005; Mendoza-Cózatl et al. 2005; Wu et al.
2006). Another option to this was to produce an in vitro gene which encodes proteins
analogous to PCs with the structure (Glu-Cys) nGly (ECs) in which all amino acids
are chemically linked through type α. Therefore, 20 units of Glu-Cys (EC) repeats
are present in the synthetic phytochelatin EC20 which has higher capability to bind
heavy metal ions in comparison to natural PCs. Production of recombinant bacterial
strains is a routine process now (Bae et al. 2000, 2001; Xu et al. 2002; Lee et al.
2002; Wu et al. 2006), but not much work is done in yeast (Schmitt et al. 2006).
Induction of EC20 can be referred to identify microorganisms with better capability
to bind heavy metal ions to use in bioremediation. MTS, PCs and ECs along with
other genetic engineering approaches have been searched to produce new recombinant microbial strains for getting these proteins to stay attached to the external
surface cell (“cell-surface display”) (Deng et al. 2003; Merle et al. 2003; Kim
330
N. Srivastava