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produced by the other organisms (Foster 2002; Haas 2003; Howard 1999; Hwang
et al. 2008; Lesuisse et al. 2002; Philpott et al. 2002; Santos et al. 2003; Van Ho
et al. 2002). The siderophore transporters such as CaSit1/CaArn1 and Sit1 present
in these organisms help in this type of siderophore uptake (Heymann et al. 2002; Hu
et al. 2002). Studies showed that the CaSitD mutant showed reduced invasion,
which ensures the significance of these proteins (Tangen et al. 2007).
11.2.4 Host Molecule-Specific Iron Acquisition
The fungi also utilize some of the host molecules as their miscellaneous iron sources
which include haem, haemoglobin, transferrin and ferritin.
Haem is a coordination complex of iron and porphyrin. It exits usually in the
form of a complex with other proteins. However, only a trace quantity of haem is
available in its free form. The oxidized form of haem is known as haemin. Fungi
such as H. capsulatum and C. albicans utilize haemin as an iron source and acquire
iron from it. The haem-binding protein Rbt5 and a haem oxygenase CaHmx1 play
a significant role in acquiring iron from haemin (Foster 2002; Pendrak et al. 2004;
Santos et al. 2003; Weissman and Kornitzer 2004). In Cryptococcus neoformans,
CigI plays an important role in haem uptake. Mutants lacking CigI showed reduced
virulence (Cadieux et al. 2013; Lian et al. 2005).
Haemoglobin, transferrin and ferritin are few iron-containing proteins present in
humans, where haemoglobin acts as a transport protein, ferritin is a storage protein
of iron and transferrin is a serum protein which has high affinity for iron.
In an iron-limiting condition, C. albicans utilizes all these proteins as their iron
sources (Almeida et al. 2009; Bairwa et al. 2017; Fourie et al. 2018; Noble 2013).
However, this iron acquisition process is dependent on several other proteins such
as a haemin receptor Rbt5 (for acquiring iron from haemoglobin) (Bairwa et al.
2017), the cell-surface adhesin protein Als3, the high-affinity iron permease
CaFtr1(for acquiring iron from ferritin) (Almeida et al. 2008; Liu and Filler 2011;
Ramanan and Wang 2000), and ferric reductase Fre10 and the high-affinity permease Ftr1 (for acquiring iron from transferrin) (Bairwa et al. 2017; Heymann et al.
2002; Knight et al. 2005).
Similarly C. neoformans utilizes transferrin as an iron source. This iron acquisition process involves Cft1, Cfo1, Ftr1 (iron permease) and Fet3 (multicopper
ferroxidase), where the ferrous iron is oxidized to ferric by Fet3 and transported
by Cft1, Cfo1 and Ftr1. The mutants without these genes showed less virulence
which ensures their importance (Jung et al. 2008). In contrast, A. fumigatus uses
siderophores to extract iron from transferrin (Hissen and Moore 2005; Hissen
et al. 2004).
A. Shanmugam et al.
produced by the other organisms (Foster 2002; Haas 2003; Howard 1999; Hwang
et al. 2008; Lesuisse et al. 2002; Philpott et al. 2002; Santos et al. 2003; Van Ho
et al. 2002). The siderophore transporters such as CaSit1/CaArn1 and Sit1 present
in these organisms help in this type of siderophore uptake (Heymann et al. 2002; Hu
et al. 2002). Studies showed that the CaSitD mutant showed reduced invasion,
which ensures the significance of these proteins (Tangen et al. 2007).
11.2.4 Host Molecule-Specific Iron Acquisition
The fungi also utilize some of the host molecules as their miscellaneous iron sources
which include haem, haemoglobin, transferrin and ferritin.
Haem is a coordination complex of iron and porphyrin. It exits usually in the
form of a complex with other proteins. However, only a trace quantity of haem is
available in its free form. The oxidized form of haem is known as haemin. Fungi
such as H. capsulatum and C. albicans utilize haemin as an iron source and acquire
iron from it. The haem-binding protein Rbt5 and a haem oxygenase CaHmx1 play
a significant role in acquiring iron from haemin (Foster 2002; Pendrak et al. 2004;
Santos et al. 2003; Weissman and Kornitzer 2004). In Cryptococcus neoformans,
CigI plays an important role in haem uptake. Mutants lacking CigI showed reduced
virulence (Cadieux et al. 2013; Lian et al. 2005).
Haemoglobin, transferrin and ferritin are few iron-containing proteins present in
humans, where haemoglobin acts as a transport protein, ferritin is a storage protein
of iron and transferrin is a serum protein which has high affinity for iron.
In an iron-limiting condition, C. albicans utilizes all these proteins as their iron
sources (Almeida et al. 2009; Bairwa et al. 2017; Fourie et al. 2018; Noble 2013).
However, this iron acquisition process is dependent on several other proteins such
as a haemin receptor Rbt5 (for acquiring iron from haemoglobin) (Bairwa et al.
2017), the cell-surface adhesin protein Als3, the high-affinity iron permease
CaFtr1(for acquiring iron from ferritin) (Almeida et al. 2008; Liu and Filler 2011;
Ramanan and Wang 2000), and ferric reductase Fre10 and the high-affinity permease Ftr1 (for acquiring iron from transferrin) (Bairwa et al. 2017; Heymann et al.
2002; Knight et al. 2005).
Similarly C. neoformans utilizes transferrin as an iron source. This iron acquisition process involves Cft1, Cfo1, Ftr1 (iron permease) and Fet3 (multicopper
ferroxidase), where the ferrous iron is oxidized to ferric by Fet3 and transported
by Cft1, Cfo1 and Ftr1. The mutants without these genes showed less virulence
which ensures their importance (Jung et al. 2008). In contrast, A. fumigatus uses
siderophores to extract iron from transferrin (Hissen and Moore 2005; Hissen
et al. 2004).
A. Shanmugam et al.