Molecular Characterization and Gene Expression Profiling ... - CUSAT

Chapter 1
Lantibiotics contain small ring structures enclosed by a thioether bond and
their structure and properties have recently been reviewed (Montville and
Chen, 1998). One of the lantibiotics, nisin, is currently used as an
antimicrobial agent for food preservation and this peptide has relatively high
activity against Gram-positive bacteria due to its specific high affinity with
Lipid II, a precursor in the bacterial cell wall synthesis (Breukink and de
Kruijff, 1999; Breukink et al., 1999). Recently synthesized six and eight
residue cyclic D,L-α-peptides have been found to exhibit high efficacy to kill
bacteria with low haemolytic activity (Fernadez-Lopez et al., 2001). Upon
binding to lipid membranes the cyclic peptides can stack to form hollow, β-
sheet-like tubular structures increasing membrane permeability. With short
size, easy to synthesize and being proteolytically stable, this class of peptides
holds considerable potential in fighting existing and emerging infectious
diseases.
1.7.7 Induction and Regulation of AMP expression
AMPs in multicellular organisms are found on external surfaces such
as the skin or the lungs or they are sequestered in granules of neutrophils,
from where they can be released to kill microbes. Some AMPs are
synthesized constitutively, for instance the histatins (Tsai and Bobek, 1998)
and human β- defensin-1 (Yang et al., 2002). Others are often induced in
response of an infection (Hoffmann et al., 1999) and thus can be considered
as acute-phase proteins, e.g. LL- 37 (Frohm et al., 1997) and human β-
defensin-2 (Harder et al., 2000; Schutte and McCray, 2002; Yang et al., 2002).
The large majority of AMPs synthesized by multicellular organisms
are encoded by the genome. Insects and mammals typically express multiple
AMPs. For example, at least ten sheep genes encode AMPs, including eight
cathelicidins and two β-defensins (Huttner et al., 1998). The bovine genome
contains genes for at least eleven cathelicidins (Scocchi et al., 1997) and over
twenty β-defensins (Ryan et al., 1998). The AMPs are produced mainly
Molecular Characterization and Gene Expression Profiling of Antimicrobial Peptides in Penaeid Shrimps
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