Molecular Characterization and Gene Expression Profiling ... - CUSAT

Chapter 2
assumed that the penaeidin proline rich region is similarly involved more in
target cell interaction than in direct antimicrobial activity. This is also
consistent with the spectrum of penaeidin antimicrobial activity, which is
directed mainly against fungi and gram-positive bacteria (Destoumieux et
al., 1999), in contrast to most of the known proline-rich peptides, which have
essentially anti-Gram-negative properties (Bulet et al., 1999).
COOH-terminal region
Since the penaeidin N -terminal region failed to exhibit antimicrobial
activity, it is tempting to speculate that the C-terminal region mediates
penaeidin antimicrobial properties. In addition, most of the antimicrobial
peptides with intramolecular disulfide bridges, such as defensins, have
antimicrobial properties similar to those observed for penaeidins. The
penaeidin C-terminal region was found to display partial conservation of a
repeated motif common to several chitin-binding proteins of the hevein
family (Allen et al., 1996). Chitin binding has also been demonstrated for
intact penaeidins but was absent for their synthetic N-terminal domain (20
amino acids) (Destoumieux et al., 1999). Thus it is believed that binding of
penaeidins to chitin, and consequently their antifungal activity, is mediated
by their C-terminal domain.
2.1.3.5. Synthesis and localization of penaeidins
In shrimp, haemocytes are the main source of penaeidin production
(Destoumieux et al., 2000a, 2000b; Munoz et al., 2002, 2003, 2004; Kang et al.,
2004). Penaeidins are constitutively expressed in their mature and active
form in granular haemocytes of naive shrimps. About 30–40% of the
circulating haemocytes express penaeidins (Meister et al., 1997). The peptides
are stored within cytoplasmic granules of granular haemocyte populations,
namely haemocytes with large granules and to a lesser extent also in
haemocytes with small granules. The population of hyaline cells is devoid of
penaeidins. The penaeidins could be secreted or released from haemocytes
Molecular Characterization and Gene Expression Profiling of Antimicrobial Peptides in Penaeid Shrimps
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