Binding of LL-37 to model biomembranes: Insight into target vs host cell recognition

Abstract

Pursuing the molecular mechanisms of the concentration dependent cytotoxic and hemolytic effects of the human antimicrobial peptide LL-37 on cells, we investigated the interactions of this peptide with lipids using different model membranes, together with fluorescence spectroscopy for the Trp-containing mutant LL-37(F27W). Minimum concentrations inhibiting bacterial growth and lipid interactions assessed by dynamic light scattering and monolayer penetration revealed the mutant to retain the characteristics of native LL-37. Although both LL-37 and the mutant intercalated effectively into zwitterionic phosphatidylcholine membranes the presence of acidic phospholipids caused augmented membrane binding. Interestingly, strongly attenuated intercalation of LL-37 into membranes containing both cholesterol and sphingomyelin (both at X=0.3) was observed. Accordingly, the distinction between target and host cells by LL-37 is likely to derive from i) acidic phospholipids causing enhanced association with the former cells as well as ii) from attenuated interactions with the outer surface of the plasma membrane of the peptide secreting host, imposed by its high content of cholesterol and sphingomyelin. Our results further suggest that LL-37 may exert its antimicrobial effects by compromising the membrane barrier properties of the target microbes by a mechanism involving cytotoxic oligomers, similarly to other peptides forming amyloid-like fibers in the presence of acidic phospholipids.

Phospholipid-driven differences determine the action of the synthetic antimicrobial peptide OP-145 on Gram-positive bacterial and mammalian membrane model systems

“…Moreover, the presence of cholesterol in POPC liposomes further reduced membrane permeabilization. This is in agreement with earlier reports that this essential mammalian membrane component attenuates the binding of AMPs [72][73][74] including LL-37 [75] concomitantly reducing toxicity of AMPs, which would be in accordance with observations that OP-145 was found to be safe in pig guinea, rabbits and rats, and primary skin and eye irritation/corrosion study, ototoxicity as well as after intravenous administration [26].…”

Alzheimer’s Disease-Associated β-Amyloid Is Rapidly Seeded by Herpesviridae to Protect against Brain Infection

“…Oligomerization is integral to normal AMP function, and soluble oligomers are the bioactive species in a range of innate immune pathways (Arnusch et al, 2007; Chu et al, 2012; Hoover et al, 2000; Oren et al, 1999; Xhindoli et al, 2014). Amyloid fibril generation is also important for AMP activities, mediating disruption of microbial cell membranes (Sood et al, 2008), neutralization of bacterial endotoxins (Wang et al, 2014), and pathogen agglutination and entrapment (Chu et al, 2012; Torrent et al, 2012). However, dysregulated AMP oligomerization can also lead to serious pathologies, including inflammation, tissue degeneration (Paulsen et al, 2002; Pereira et al, 1996; Reinholz et al, 2012; Scarpa et al, 2012), and deposition as amyloid in at least three human amyloidopathies (Araki-Sasaki et al, 2005; Ciornei et al, 2006; Kee et al, 2008; Linke et al, 2005; Millucci et al, 2011; Pálffy et al, 2009; Reinholz et al, 2012; Scarpa et al, 2012; Yamaguchi et al, 2007; Zhao et al, 2008).…”

Common mechanism unites membrane poration by amyloid and antimicrobial peptides

“…The current research, along with the recent discovery that IAPP has cellpenetrating characteristics and targets intracellularly to mitochondrial membranes (22), supports the idea that cytotoxicity in amyloid disease is a direct consequence of this activity being directed against the organism's own membranes. Conversely, other work has shown that the antimicrobial peptides protegrin-1 (44) and LL-37 (45) are capable of forming amyloid-like fibrils, suggesting the possibility of a relationship between a peptide's amphipathic, porating character and its amyloidogenicity. Furthermore, the characteristics of membrane leakage induced by IAPP (13) and magainin 2 (14) bear similarities to those of the proapoptotic protein Bax (46).…”