Melittin

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-... 

The pain appears to arise from the formation of melittin pores in the membranes of nociceptors, free nerve endings that detect harmful ( noxious —thus the name) stimuli of violent mechanical stress, high temperatures, and irritant chemicals. The creation of pores by melittin depends on the nociceptor membrane potential. Melittin in water solution is tetrameric. However, melittin interacting with membranes in the absence of a membrane potential is monomeric and shows no evidence of oligomer... 

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

Bumble bee venom contains also a phospholipase A2 with partial identity to bee venom phospholipase Aj and a protease, but no melittin. Instead there are several small peptides called bombolitins [9]. There is limited cross-reactivity between honey bee and bumblebee venoms [2]. 

Chen CP, Kim JS, Steenblock E, Liu D, Rice KG (2006) Gene transfer with poly-melittin... 

Boeckle S, Fahrmeir J, Roedl W, Ogris M, Wagner E (2006) Melittin analogs with high lytic activity at endosomal pH enhance transfection with purified targeted PEI polyplexes. J Control Release 112 240-248... 

Meyer M, Zintchenko A, Ogris M, Wagner E (2007) A dimethylmaleic acid-melittin-polylysine conjugate with reduced toxicity, pH-triggered endosomolytic activity and enhanced gene transfer potential. J Gene Med 9 797-805... 

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... 

The interaction between melittin (a 26 a.a. peptide that exhibits potent anti-microbial activity)90 92 and lipopolysaccharides (the major constituent of the outer membrane of the Gram-negative bacteria) has been studied by NMR. It was demonstrated that the C-terminus of melittin adopts a helical structure in the complex with LPS, while the Y-terminus appears in an extended conformation. STD experiments permitted to identify those residues of melittin in close proximity with LPS, which appeared to be located at the C-terminus and thus, engaged in the formation of helical structure. 

Runnels LW, Scarlata SF (1995) Theory and application of fluorescence homotransfer to melittin oligomerization. Biophys J 69 1569-83... 

GTP gamma S binding proteins from membranes of porcine brain Purification, comparison with conventional column Anion Exchange and Affinity (Melittin) disks [82]... 

On the other hand, basic myelin protein and monomeric melittin are proteins which, by many criteria, are devoid of ordered structure in aqueous solutions. This results in freedom of rotation of tryptophan residues which are exposed to the solvent. Such a situation may exist for peptides without regular structure and for denatured proteins. 

Figure 2.10. The dependence of the position of the fluorescence spectrum maximum on excitation wavelength for 2,6-TNS in model media (a) and in complexes with proteins (b). (a) 2,6-TNS (3 x 10-s) M in glucose glass at 20°C (1), glycerol at +1°C (2), and 80% aqueous ethanol at 20°C (3). Excitation spectra are for glycerol (4) and 80% ethanol (5). (b) 2,6-TNS in complexes with / -lactoglobulin (1), tetrameric melittin (2), human serum albumin (3), and lysozyme (4) at 20°C. Excitation spectrum (5) is for human serum albumin.

Figure 2.11. The dependence of the position of the fluorescence spectrum maximum on excitation wavelength for tryptophan in a model medium (glycerol) at different temperatures (a) and singletryptophan proteins (b). 1, Whiting parvalbumin, pH 6.S in the presence of Ca2+ ions 2, ribonuclease Th pH 6.5 3, ribonuclease C2, pH 6.5 4, human serum albumin, pH 7.0, +10"4 M sodium dodecyl sulfate 5, human serum albumin, pH 3.2 6, melittin, pH 7.5, +0.15 M NaCl 7, protease inhibitor IT-AJ from Actinomyces janthinus, pH 2.9 8, human serum albumin, pH 7.0 9, -casein, pH 7.5 10, protease inhibitor IT-AJ, pH 7.0 11, basic myelin protein, pH 7.0 12, melittin in water. The dashed line is the absorption spectrum of tryptophan.

Let us consider in greater detail the temperature dependence of the position of the maximum in the fluorescence spectrum of melittin (Figure 2.12). Three characteristic temperature regions may be distinguished. At T< 30 °C the spectrum does not depend on the temperature with excitation at both 280 nm and 305 nm in this case the red-edge effect is maximal. Evidently, the condition xR xF holds in this region. In the range 30 to 50 °C there is a... 

Figure 2.12. (a) The dependence of the position of the fluorescence spectrum maximum of tetrameric melittin on temperature at excitation wavelengths 280 (1) and 305 nm (2). (b) The dependence of logxR on 1/T, calculated from these data using Eq. (2.10). 

S. Georghiou, M. Thompson, and A. H. Mukhopadhyay, Melittin-phospholipid interaction. Evidence for melittin aggregation, Biochim. Biophys. Acta 642, 429-432 (1981). 

Xue, Q., Dunayevskiy, Y. M., Foret, F., and Karger, B. L. (1997). Integrated multichannel microchip electrospray ionization mass spectrometry analysis of peptides from on-chip tryptic digestion of melittin. Rapid Commun. Mass Spectrom. 11, 1253 — 1256. 

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