title: Effect of ionic strength on the organization and dynamics of membrane-bound melittin.
abstract: Melittin, a cationic hemolytic peptide, is intrinsically fluorescent due to the presence of a single functionally important tryptophan residue. We have previously shown that the sole tryptophan of melittin is localized in a motionally restricted environment in the membrane interface. We have monitored the effect of ionic strength on the organization and dynamics of membrane-bound melittin utilizing fluorescence and circular dichroism (CD) spectroscopic approaches. Our results show that red edge excitation shift (REES) of melittin bound to membranes is sensitive to the change in ionic strength of the medium. This could be attributed to a change in the immediate environment around melittin tryptophan with increasing ionic strength due to differential solvation of ions. Interestingly, the rotational mobility of melittin does not appear to be affected with change in ionic strength. In addition, fluorescence parameters such as lifetime and acrylamide quenching of melittin indicate an increase in water penetration in the membrane interface upon increasing ionic strength. Our results suggest that the solvent dynamics and water penetration in the interfacial region of the membranes are significantly affected at physiologically relevant ionic strength. These results assume significance in the overall context of the influence of ionic strength in the organization and dynamics of membrane proteins and membrane-active peptides.
authors.affiliation: Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500 007, India.
authors.forename: H
authors.initials: H
authors.lastname: Raghuraman
authors.forename: Sourav
authors.initials: S
authors.lastname: Ganguly
authors.forename: Amitabha
authors.initials: A
authors.lastname: Chattopadhyay
mesh_terms: D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism*; D002942:Circular Dichroism; D005454:Fluorescence Polarization; D007477:Ions / Q000737:chemistry; D008555:Melitten / Q000737:chemistry* / Q000378:metabolism*; D009994:Osmolar Concentration; D011485:Protein Binding; D017433:Protein Structure, Secondary
chemical_list: D007477:Ions; D008555:Melitten