The role of electrostatic interactions in the membrane binding of melittin

Abstract

The binding of melittin and the C-terminally truncated analogue of melittin (21Q) to a range of phospholipid bilayers was studied using surface plasmon resonance (SPR). The phospholipid model membranes included zwitterionic dimyristylphosphatidylcholine (DMPC) and dimyristylphosphatidylethanolamine (DMPE), together with mixtures DMPC/dimyristylphosphatidylglycerol (DMPG), DMPC/DMPG/cholesterol and DMPE/DMPG. Melittin bound rapidly to all membrane mixtures, whereas 21Q, which has a reduced charge, bound much more slowly on the DMPC and DMPC/DMPG mixtures reflecting the role of the initial electrostatic interaction. The loss of the cationic residues also significantly decreased the binding of 21Q with DMPC/DMPG/Cholesterol, DMPE and DMPE/DMPG. The role of electrostatics was also highlighted with NaCl in the buffer, which affected the way melittin bound to the different membranes, causing a more uniform, concentration dependant increase in response. The biosensor results were correlated with the conformation of the peptides determined by circular dichroism analysis, which indicated that high α-helicity was associated with high binding affinity. Overall, the results demonstrate that the positively charged residues at the C-terminus of melittin play an essential role in membrane binding, that modulation of peptide charge influences selectivity of binding to different phospholipids and that manipulation of the cationic regions of antimicrobial peptides can be used to modulate membrane selectivity.

Role of the Cationic C-Terminal Segment of Melittin on Membrane Fragmentation

“…The present results therefore reveal that the C-terminal charges of melittin reduce the affinity of the peptide for neutral membranes. These conclusions are in contradiction with those inferred from the SPR binding studies concluding that truncated amidated melittin-21Q exhibits, relative to melittin, a lower or a similar affinity for DMPC membranes 45,46 . These SPR experiments were conducted on supported bilayers and the nature …”

“…For instance, the properties of melittin-21Q, a truncated analogue of melittin in which residues 21 to 25 (K 21 -R 22 -K 23 -R 24 -Q 25 ) were omitted, were investigated. Its binding to zwitterionic 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) bilayers as well as to anionic 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) bilayers was measured by Surface Plasmon Resonance (SPR) [45][46] . Melittin-21Q exhibited a reduced or similar binding to DMPC and to DMPG bilayers compared to native melittin, suggesting a favorable or a limited contribution of the cationic C-terminal portion to membrane affinity.…”

A model for membrane potential and intracellular ion distribution

“…The other line of evidence for electrostatic interactions between phospholipids and positively charge molecules comes from the work on artificial lipid vesicles (Benfenati et al, 1989;Ben-Tal et al, 1997;Ben-Tal et al, 1996;Chen et al, 1997;Higgins and Mann, 1983;Hoernke et al, 2012;Kimelberg and Papahadjopoulos, 1971;Mertins and Dimova, 2011;Murray et al, 1999;Terzi et al, 1994;Zhang et al, 1998) or plane lipid layers (Cevc and Marsh, 1983;Hall et al, 2011;Hoernke et al, 2012;Salay et al, 2012). However, flat membranes or the outer surface of vesicles represent a different electrical environment, and there is no contradiction between those results and our hypothesis.…”

Melittin peptides exhibit different activity on different cells and model membranes

“…1) in which residues 1-20 are hydrophobic and residues 21-26 are hydrophilic (Raghuraman and Chattopadhyay 2004). MLT can target live cells such as red blood cells and binds to lipid membranes spontaneously leading to lipid bilayer disruption and hemolysis (Lam et al 2001(Lam et al , 2002Hincha and Crowe 1996;Chattopadhyay 2004, 2007;Sessa et al 1969;Tomoyoshi et al 2013;Lad et al 2007;Hall et al 2011;Zhao et al 1995). MLT is also known to have anticancer properties (Gajski and Garaj-Vrhovac 2013).…”