metal ion transporter: MntH Groups A, B, C, and (4) natural resistance-associated
macrophage protein (NRAMP) family (Jakubovics and Jenkinson 2001; Cellier
2002; Papp-Wallace and Maguire 2006). Metallochaperones are responsible for the
incorporation of correct metal into some of the proteins; however, most metalloproteins acquire their metals directly from cellular pools. In an attempt to understand the cellular mechanisms that govern metal acquisition by most nascent
proteins, Tottey et al. (2008) identified the most abundant Cu
2+ -protein, CucA
and the most abundant Mn
2+ -protein, MncA in the periplasm of cyanobacteria
Synechocystis PCC 6803. They showed that compartmentalization kept competitive
metals out of the wrong nascent proteins during protein folding.
The only Mn-oxidizing proteins identified and characterized so far in bacteria
were the MCOs (Brouwers et al. 2000b; Francis and Tebo 2000). Another class of
proteins in bacteria rarely known to oxidize Mn is the heme-containing manganese
peroxidases (MNPs) (Palma et al. 2000; Anderson et al. 2009b). The known
Mn-oxidizing proteins include the MnxG (~138 kDa) of Bacillus SG-1 (van
Wassbergen et al. 1996; Francis et al. 2002) and MopA of Aurantimonas manganoxidans Strain. SI85-9A1 and Erythrobacter sp Strain. SD-21[Anderson et al.
(2009b)]. In marine a-Proteobacterium SD-21, manganese-oxidizing factors of
%250 and 150 kDa was observed in the logarithmic phase of growth. However,
the expression of Mn(II) oxidase was not completely dependent on Mn
2+ rather
it was required for higher growth yield (Francis et al. 2001). They claimed it as the
first group of Mn-containing metalloenzyme in gram-negative marine bacteria.
Francis and Tebo (2002) could identify the first active Mn-oxidizing enzymes in
spores or gram-positive bacteria. Their study came across proteins of different
molecular weights in Mn-oxidizing marine Bacillus sp isolated from coastal marine
sediment. Based on the inhibition of Mn-oxidizing activity by azide a multicopper
oxidase inhibitor suggested that the unidentified proteins belong to the MCO group
of enzymes. The role of metalloregulatory protein MntR, a transcriptional regulator
of Mn homeostasis, was determined by Lieser et al. (2003). They demonstrated that
differences in metal-activated DNA binding could play a role in the mechanism of
Mn(II)-selective transcription of factors and the oligomerization of MntR that was
metal independent. Further, Huang and Wu (2004) revealed the identity of the
genes under control of manganese response regulator ManR in the cyanobacterium,
Anabaena sp. PCC 7120.
The known Mn-oxidizing proteins include the CumA (50.5 kDa) of Pseudomonas putida GB-1 (Brouwers et al. 1999), MofA (~180 kD) of Leptothrix discophora
SS-1 (Corstjens et al. 1997; Brouwers et al. 2000a), and MoxA (52.47 kDa) of
Pedomicrobium sp. ACM3067 (Ridge et al. 2007). Several regulatory pathways for
Mn in bacteria were investigated by different authors. Que and Helmann (2000),
Guedon et al. (2003), and Moore and Helmann (2005) found that MntR, Fur, TnrA,
and s
B regulons regulated Mn uptake in Bacillus subtilis. Platero et al. (2004)
stated that Fur was involved in manganese-dependent regulation of mntA. Patzer
and Hantke (2001) and Hohle and O’Brian (2009) provided evidence to show that
mntH gene encoding NRAMP like Mn
2+ transporter was repressed by Fur and
MntR of the mntH gene. Conversely, Kehres et al. (2000) inferred that NRAMP
62
P.P. Sujith and P.A. Loka Bharathi
macrophage protein (NRAMP) family (Jakubovics and Jenkinson 2001; Cellier
2002; Papp-Wallace and Maguire 2006). Metallochaperones are responsible for the
incorporation of correct metal into some of the proteins; however, most metalloproteins acquire their metals directly from cellular pools. In an attempt to understand the cellular mechanisms that govern metal acquisition by most nascent
proteins, Tottey et al. (2008) identified the most abundant Cu
2+ -protein, CucA
and the most abundant Mn
2+ -protein, MncA in the periplasm of cyanobacteria
Synechocystis PCC 6803. They showed that compartmentalization kept competitive
metals out of the wrong nascent proteins during protein folding.
The only Mn-oxidizing proteins identified and characterized so far in bacteria
were the MCOs (Brouwers et al. 2000b; Francis and Tebo 2000). Another class of
proteins in bacteria rarely known to oxidize Mn is the heme-containing manganese
peroxidases (MNPs) (Palma et al. 2000; Anderson et al. 2009b). The known
Mn-oxidizing proteins include the MnxG (~138 kDa) of Bacillus SG-1 (van
Wassbergen et al. 1996; Francis et al. 2002) and MopA of Aurantimonas manganoxidans Strain. SI85-9A1 and Erythrobacter sp Strain. SD-21[Anderson et al.
(2009b)]. In marine a-Proteobacterium SD-21, manganese-oxidizing factors of
%250 and 150 kDa was observed in the logarithmic phase of growth. However,
the expression of Mn(II) oxidase was not completely dependent on Mn
2+ rather
it was required for higher growth yield (Francis et al. 2001). They claimed it as the
first group of Mn-containing metalloenzyme in gram-negative marine bacteria.
Francis and Tebo (2002) could identify the first active Mn-oxidizing enzymes in
spores or gram-positive bacteria. Their study came across proteins of different
molecular weights in Mn-oxidizing marine Bacillus sp isolated from coastal marine
sediment. Based on the inhibition of Mn-oxidizing activity by azide a multicopper
oxidase inhibitor suggested that the unidentified proteins belong to the MCO group
of enzymes. The role of metalloregulatory protein MntR, a transcriptional regulator
of Mn homeostasis, was determined by Lieser et al. (2003). They demonstrated that
differences in metal-activated DNA binding could play a role in the mechanism of
Mn(II)-selective transcription of factors and the oligomerization of MntR that was
metal independent. Further, Huang and Wu (2004) revealed the identity of the
genes under control of manganese response regulator ManR in the cyanobacterium,
Anabaena sp. PCC 7120.
The known Mn-oxidizing proteins include the CumA (50.5 kDa) of Pseudomonas putida GB-1 (Brouwers et al. 1999), MofA (~180 kD) of Leptothrix discophora
SS-1 (Corstjens et al. 1997; Brouwers et al. 2000a), and MoxA (52.47 kDa) of
Pedomicrobium sp. ACM3067 (Ridge et al. 2007). Several regulatory pathways for
Mn in bacteria were investigated by different authors. Que and Helmann (2000),
Guedon et al. (2003), and Moore and Helmann (2005) found that MntR, Fur, TnrA,
and s
B regulons regulated Mn uptake in Bacillus subtilis. Platero et al. (2004)
stated that Fur was involved in manganese-dependent regulation of mntA. Patzer
and Hantke (2001) and Hohle and O’Brian (2009) provided evidence to show that
mntH gene encoding NRAMP like Mn
2+ transporter was repressed by Fur and
MntR of the mntH gene. Conversely, Kehres et al. (2000) inferred that NRAMP
62
P.P. Sujith and P.A. Loka Bharathi