Cecropin

Recently, a variety of natural peptides that form transmembrane channels have been identified and characterized. Melittin (Figure 10.35) is a bee venom toxin peptide of 26 residues. The cecropins are peptides induced in Hyalophora cecropia (Figure 10.36) and other related silkworms when challenged by bacterial infections. These peptides are thought to form m-helical aggregates in mem-... 

Chri.sten.sen, B., et al., 1988. Channel-forming propertie.s of cecropin.s and related model compound.s incorporated into planar lipid mem-brane.s. Proceedings of the National Academy of Sciences U.S.A. 85 5072—5076. 

The rate of transport across bilayer membranes reconstituted from dipalmitoylphosphatidylcholine (DPPC) andnigericin is approximately the same as that observed across membranes reconstituted from DPPC and cecropin a at 35 C. Would you expect the transport rates across these two membranes also to be similar at 50 C Explain. 

Bechinger, B. Structure and functions of channel-forming peptides Magainins, cecropins, melittin, and alamethicin. /. Memhr. Biol. 1997, 756, 197-211. 

Ferre R, Badosa E, Feliu L, Planas M, Montesinos E, Bardaji E (2006) Inhibition of plant-pathogenic bacteria by short synthetic cecropin A-melittin hybrid peptides. Appl Environ Microbiol 72 3302-3308... 

Proteins cecropins (induced from immune resprxise in Hyalophora cecropia L., Lepidoptera, and other Ins. frcm various regions MI). 

Figure 1. Stick-figure representations of the peptide backbone of magainin 2, cecropin A, and lactacin F. Top, end view of a-helix bottom, side view. Structures were obtained using HyperChem software.

Melittin, a 26-amino acid amphipathic a-helical peptide that occurs in bee venom, has recently been found capable of suppressing HIV-1 gene expression. Melittin inhibits HIV-1 infection in both acutely and persistently infected t-lymphoma (KE37/1) and fibroblastoid (LC5) cells at an IC50 of 0.5 to 1.5 iM this effect is apparently mediated by a direct suppressive action on the HIV long terminal repeat (LTR). Antimicrobial peptides such as melittin (honeybees), cecropin (moths), and magainin (frogs) may thus inhibit cell-associated HIV-1 production at the transcription level. 

Cecropin B Hemolymph of Hyalophom cecropia KWKVFKKIEKMGRNIRN GIVKAGPAIAVLGEAKAL- nh2 a-Helical 1.7 (pM) >100 (pM) (40)... 

Gudmundsson, G.M., Lidholm, D.-A., Asling, B Gan, R and Boman, H.G. (1991) The cecropin locus. Cloning and expression of a gene cluster encoding three antibacterial peptides in Hyalaphora cecropia. J. Biol. Chem. 266, 11510-11517. 

Boman, H. G., Agerberth, B. and Boman, A. (1993) Mechanisms of action on Escherichia coli of cecropin PI and PR-39, two antibacterial peptides from pig intestine. Infect. Immun. 61, 2978-2984. 

Another study on expression of an insect cecropin in E. coli used a fusion to the thioredoxin protein (Xu et al., 2007b). In this case the Musca domestica (house fly) cecropin termed Mdmcec was cloned downstream of the thioredoxin with an intervening His-tag for purification and enterokinase (Table 2) cleavage site (bold) for release of peptide... 

CBla, novel anticancer peptide derived from natural AMP cecropin B Jingzhaotoxin-VII... 

One of the most well-known examples of insect toxins is melittin, a bee venom peptide with potent haemolytic activity. Melittin adopts an a-helical conformation, and has been extensively characterised using a range of techniques, including both solution- and solid-state NMR spectroscopy.176 Some helical peptides with antimicrobial activity have also been found in wasps, such as eumenine mastroparan-AF (EMP-AF-NH2) from the venom of the solitary wasp Anterhynchium flavormarginatum micado,177 and the cecropins found in the haemolymph of Hyalophora cecropia.178 Several of these peptides have cytotoxic activity and are potential anticancer agents.179... 

Cecropins 224) are produced in insects on account of the lack of lymphocytes and immunoglobulins by a humoral immune reaction, and have a broad spectrum of antibacterial activity. 

Cecropin A analogs (Fig. 18) have been synthesized by Andreu et al. 225) by the solid-phase method. 

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