Molecular Characterization and Gene Expression Profiling ... - CUSAT

Chapter 1
quite opposite characteristics with respect to antibacterial activity. Indeed,
different peptides may be membrane permeabilizing at their minimal
effective concentrations or at concentrations well above or well below these
concentrations. Nonetheless, antibacterial peptides seem largely able to affect
their antimicrobial activity because of their amphipathicity or amphiphilicity
and because of the presence of regions within the folded structure with high
concentrations of positively charged residues (Powers et al., 2004).
Mechanism of antibacterial activity
As described in section 1.1.3.9.
1.7.10.7 Antifungal peptides
Knowledge of antifungal peptides has accelerated in recent years.
Their mode of action was first described as involving either fungal cell lysis
or interference with fungal cell wall synthesis (de Lucca and Walsh, 1999).
However, as the numbers of known antifungal peptides increase, new modes
of action are being identified. It is intriguing to note that peptides with
primarily antifungal activity, such as many of those isolated from plants,
tend to be relatively rich in polar and neutral amino acids, suggesting a
unique structure-activity relationship (Lustig et al., 1996).
Structural requirements for antifungal peptides
Studies have shown that antifungal peptides vary substantially in
sequence and structure, and peptides as structurally diverse as eucommia
(Huang et al., 2004), the α-helical P18 (Lee et al., 2004), and the extended
peptide indolicidin (Lee et al., 2003), as well as plant defensins and a
coleopteran β-sheet peptide from Acrocinus longimanus (Barbault et al., 2003),
have all shown antifungal activity. Thus, like for antibacterial peptides, there
are no obvious conserved structural domains that give rise to antifungal
activity. Modification of ineffective AMPs has revealed that relatively
modest changes often result in antifungal activity. Although no conserved
sequences are evident for the antifungal peptides, several have been
Molecular Characterization and Gene Expression Profiling of Antimicrobial Peptides in Penaeid Shrimps
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