The increased bactericidal activity of a fatty acid-modified synthetic antimicrobial peptide of human cathepsin G correlates with its enhanced capacity to interact with model membranes.
The bactericidal potency of a synthetic peptide (CG 117-136) of human lysosomal cathepsin G (cat G) can be substantially increased by covalent attachment to its N- or C-termini, of saturated, linear fatty acids (FAs), namely those with C-8, C-10 and C-12 hydrocarbon chains. In order to understand better the mechanism by which FA moieties increase the bactericidal activity of CG 117-136, the interaction of N-terminally FA-modified peptides with artificial membranes was studied. First, the content of secondary structure motifs in the modified and unmodified peptides was determined by circular dichroism (CD). A marked increase in the propensity of FA-modified CG 117-136 to form an alpha-helix structure was observed for the C-8, C-10 and C-12 derivatives compared with unmodified/short-chain and long-chain (C-14, C-16, C-18) derivatives. These effects were observed both in the presence of large unilamellar liposomes or in trifuluoroethanol, a membrane-stimulating agent. Second, the capacity of peptides to insert into large unilamellar liposomes as a function of FA length was determined by their ability to release a trapped fluorescent dye. FA derivatives with the highest alpha-helical content were found to be the most effective in releasing a fluorescent dye, compared with an unmodified peptide and/or derivatives having a low alpha-helical content. The ability of the peptides to attain alpha-helical structure in the membrane-like environment and the ability to disrupt the liposomal membrane, therefore correlate remarkably well with their increased ability to kill bacteria. A plausible explanation for improved bactericidal action of the modified peptide is that the FA moiety facilitates formation of the peptide with an alpha-helical structure formation in membranes, which is essential for disrupting the integrity of the bacterial cytoplasmic membrane.
Mak
Pawel
P
Institute of Molecular Biology, Jagiellonian University, Gronostajowa 7, 30-387 Krakow, Poland.
Pohl
Jan
J
Dubin
Adam
A
Reed
Matthew S
MS
Bowers
Samera E
SE
Fallon
Michael T
MT
Shafer
William M
WM
D000595:Amino Acid Sequence; D001419:Bacteria / Q000187:drug effects*; D002462:Cell Membrane / Q000187:drug effects; D005227:Fatty Acids / Q000494:pharmacology*; D036341:Intercellular Signaling Peptides and Proteins; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry / Q000494:pharmacology*; D013329:Structure-Activity Relationship
C102462:CG 117136; D005227:Fatty Acids; D036341:Intercellular Signaling Peptides and Proteins; D011506:Proteins