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defensin, it kills M. bovis-BCG by degranulation. It exhibits potent antimycobacterial activity at micromolar concentrations.
15.4.2 RNase 7
RNase 7 also belongs to RNase A superfamily, which participates in the host
immune response against pathogen infection. They are considered to be one of the
main components of first-line protection of the innate immunity at the epithelial
level. Harder and Schroder (2002), while analyzing healthy human skin for the presence of endogenous antimicrobial peptides, were able to identify a novel 14.5 kDa
peptide and named it RNase 7. They demonstrated that RNase 7 was able to exhibit
potent in vitro antimicrobial activity against various bacterial species and certain
yeast species. Later Zhang et al. (2003) identified and cloned the corresponding
RNase7 gene in Escherichia coli. They demonstrated that low micromolar concentration of RNase 7 inhibited bacterial growth. RNase 7 has high ribonuclease activity, which is not required for microbial inhibition. Huang et al. (2007) mutated the
histidines and lysines to alanine at its catalytic site, to generate H15A, H123A and
K38A recombinant RNase 7 peptide. The recombinant peptides were devoid of
ribonuclease activity without loss of their antimicrobial activity against Pseudomonas
aeruginosa. A similar experiment by Koten et al. (2009) using H123A peptide demonstrated its antimicrobial activity against Enterococcus faecium and E. coli. Pulido
et al. (2013) have shown that RNase 7 works independently of its ribonuclease
activity and exhibits mycobacterial growth inhibition at micromolar ranges. They
also identified the active domain in RNase 3 and RNase 7 to be the N-terminal
region of the peptide. The mechanism of action was due to change in the membrane
polarity of the microbe by the AMP, leading to loss of membrane integrity and cell
death.
15.5 Inhibitors of Cytoplasmic Components
15.5.1 F 1 -F 0 ATPase Inhibitors
Magainins (Zasloff 1987) are peptides with broad-spectrum antimicrobial activity
isolated from the skin of Xenopus laevis. The peptide was demonstrated to have
(Morvan et al. 1994) antibacterial and antiparasitic activities. Magainins do not lyse
non dividing mammalian cells. Magainin-I analog peptide (MIAP) is a de novo
synthesized antimycobacterial peptide, which showed two-fold higher antimycobacterial activity than its natural analog magnanin-1. The peptide was found to act
on F 1 F 0 -ATPase of Mycobacterium with magainin-1 inhibiting the ATPase activity
to 30% and the de novo peptide MIAP completely abolishing the F 1 F 0 -ATPase. The
antimycobacterial action of the peptide is brought about by a change in the internal
pH of the organism (Santos et al. 2012).
S.M. Thayil and A.K. Kesavan
defensin, it kills M. bovis-BCG by degranulation. It exhibits potent antimycobacterial activity at micromolar concentrations.
15.4.2 RNase 7
RNase 7 also belongs to RNase A superfamily, which participates in the host
immune response against pathogen infection. They are considered to be one of the
main components of first-line protection of the innate immunity at the epithelial
level. Harder and Schroder (2002), while analyzing healthy human skin for the presence of endogenous antimicrobial peptides, were able to identify a novel 14.5 kDa
peptide and named it RNase 7. They demonstrated that RNase 7 was able to exhibit
potent in vitro antimicrobial activity against various bacterial species and certain
yeast species. Later Zhang et al. (2003) identified and cloned the corresponding
RNase7 gene in Escherichia coli. They demonstrated that low micromolar concentration of RNase 7 inhibited bacterial growth. RNase 7 has high ribonuclease activity, which is not required for microbial inhibition. Huang et al. (2007) mutated the
histidines and lysines to alanine at its catalytic site, to generate H15A, H123A and
K38A recombinant RNase 7 peptide. The recombinant peptides were devoid of
ribonuclease activity without loss of their antimicrobial activity against Pseudomonas
aeruginosa. A similar experiment by Koten et al. (2009) using H123A peptide demonstrated its antimicrobial activity against Enterococcus faecium and E. coli. Pulido
et al. (2013) have shown that RNase 7 works independently of its ribonuclease
activity and exhibits mycobacterial growth inhibition at micromolar ranges. They
also identified the active domain in RNase 3 and RNase 7 to be the N-terminal
region of the peptide. The mechanism of action was due to change in the membrane
polarity of the microbe by the AMP, leading to loss of membrane integrity and cell
death.
15.5 Inhibitors of Cytoplasmic Components
15.5.1 F 1 -F 0 ATPase Inhibitors
Magainins (Zasloff 1987) are peptides with broad-spectrum antimicrobial activity
isolated from the skin of Xenopus laevis. The peptide was demonstrated to have
(Morvan et al. 1994) antibacterial and antiparasitic activities. Magainins do not lyse
non dividing mammalian cells. Magainin-I analog peptide (MIAP) is a de novo
synthesized antimycobacterial peptide, which showed two-fold higher antimycobacterial activity than its natural analog magnanin-1. The peptide was found to act
on F 1 F 0 -ATPase of Mycobacterium with magainin-1 inhibiting the ATPase activity
to 30% and the de novo peptide MIAP completely abolishing the F 1 F 0 -ATPase. The
antimycobacterial action of the peptide is brought about by a change in the internal
pH of the organism (Santos et al. 2012).
S.M. Thayil and A.K. Kesavan