Effect of ionic strength on folding and aggregation of the hemolytic peptide melittin in solution

Abstract

Melittin is a cationic, amphipathic, hemolytic peptide composed of 26 amino acid residues. It is intrinsically fluorescent due to the presence of a single tryptophan residue, which has been shown to be crucial for its hemolytic activity. It undergoes a structural transition from a random coil monomer to an alpha-helical tetramer at high ionic strength. Although the aggregation behavior of melittin in solution is well characterized, dynamic information associated with the aggregation of melittin is lacking. In this paper, we have monitored the effect of ionic strength on the dynamics and aggregation behavior of melittin in aqueous solution by utilizing sensitive fluorescence approaches, which include the red edge excitation shift (REES) approach. Importantly, we demonstrate that REES is sensitive to the self-association of melittin induced by ionic strength. The change in environment experienced by melittin tryptophan(s) is supported by changes in fluorescence emission maximum, polarization, and lifetime. In addition, the accessibility of the tryptophan residue was probed by fluorescence quenching experiments using acrylamide and trichloroethanol as soluble and hydrophobic quenchers, respectively. Circular dichroism studies confirm the ionic strength-induced change in the secondary structure of melittin. Taken together, these results constitute the first report showing that REES could be used as a sensitive tool to monitor the aggregation behavior of melittin in particular and other proteins and peptides in general.

Melittin: a Membrane-active Peptide with Diverse Functions

“…This is in agreement with fluorescence experiments which show that melittin is predominantly monomeric at very low salt concentration (Quay and Condie 1983;Raghuraman and Chattopadhyay 2006a). In contrast, the aggregation of melittin is promoted by high concentration of the peptide and/or high ionic strength at neutral pH (Talbot et al 1979;Faucon et al 1979;Raghuraman and Chattopadhyay 2006a). The effect of increasing melittin concentration on tetramer formation has been supported by an increase in the helical content of the peptide (Bello et al 1982).…”

“…Conformation of one melittin chain from the tetramer is shown below (Terwilliger and Eisenberg, 1982) monomeric and adopts a random coil conformation when the peptide concentration and ionic strength are low at physiological pH. This is in agreement with fluorescence experiments which show that melittin is predominantly monomeric at very low salt concentration (Quay and Condie 1983;Raghuraman and Chattopadhyay 2006a). In contrast, the aggregation of melittin is promoted by high concentration of the peptide and/or high ionic strength at neutral pH (Talbot et al 1979;Faucon et al 1979;Raghuraman and Chattopadhyay 2006a).…”

“…We have recently shown that the red edge excitation shift (REES) approach (Demchenko 1988;Chattopadhyay 2003; could be used as a convenient tool to monitor the aggregation behavior of melittin in aqueous solution (Raghuraman and Chattopadhyay 2006a). REES represents a powerful approach which can be used to directly monitor the environment and dynamics around a fluorophore in a complex biological system (Demchenko 2002;Chattopadhyay 2003;).…”

Dithizone-etched CdTe nanoparticles-based fluorescence sensor for the off–on detection of cadmium ion in aqueous media

“…It can be seen that whether the uorescence is quenched by dithizone or restored by Cd 2+ , the uorescence intensity is the best in ultrapure water, which may be attributed to the ionic strength effect. 40 Therefore, ultrapure water was chosen throughout the experiment.…”

Melittin: A Key Composition of Honey Bee Venom with Diverse Pharmaceutical Function

“…In aqueous solution, the monomeric melittin self-assembly to a tetramer is increased with elevated ionic, melittin concentration, and high pH. The fluorescence experiments shown that melittin for the most part was monomeric at very low ionic resolution [13]. On the contrary, high ionic strength and high concentration of the peptide promoted the aggregation at neutral pH solution.…”