A Bactericidal Cecropin-A Peptide with a Stabilized α-Helical Structure Possess an Increased Killing Capacity But No Proinflammatory Activity

Abstract

Antibacterial peptides are part of the innate immune system in a variety of different species including humans. Some of these peptides have also been shown to have effects on immune competent cells such as professional phagocytes. We have recently shown that a cecropin-like peptide from Helicobacter pylori, Hp(2-20), in addition to being bactericidal possesses proinflammatory effects and can recruit and activate neutrophils as well as monocytes. It is well established that cecropins have the ability to adopt amphipathic alpha-helices, which is thought to be required for their bactericidal activity. In this study we show the same structural requirements for Hp(2-20). Breaking the helical structure of Hp(2-20) reduced the antibacterial effect and abolished its proinflammatory activity. A C-terminal truncated cecropin A peptide that highly resembles Hp(2-20) failed to activate neutrophils and computer-based structural simulations revealed a difference between the two peptides in the stability of their helical structures. A hybrid peptide with amino acid substitutions stabilizing the alpha-helical structure of the truncated cecropin A peptide did not introduce any proinflammatory activity; the bactericidal activity was, however, increased. We thus conclude that the proinflammatory effect of Hp(2-20) is a unique sequence-specific feature of the peptide and the ability to adopt a stable amphipathic helix is a necessary but not sufficient criterion for the functional dualism of the peptide.

Interleukin-8-Derived Peptide Has Antibacterial Activity

“…In light of the results that also acid hydrolysis of IL-8 generates an antibacterial peptide; studies of the peptide in relation to antibacterial/inflammatory activities in the acidic environment of the intestine would be of interest. This is further emphasized when considering the similarity and cooperative mode of action for the H. pylori derived peptide Hp (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) and the IL-8 peptide.…”

“…No functional difference between the two peptides was found, and both are referred to as the IL-8 peptide. The cecropin-like peptide Hp (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20), with a sequence corresponding to the amino-terminal part of ribosomal protein L1 in H. pylori (AKKVFKRLEKLFSKIQNDK), was synthesized and high-pressure liquid chromatography purified by Innovagen (Lund, Sweden). The peptides were dissolved in water and stored at Ϫ70°C until used.…”

“…The cecropin-like peptide Hp (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20), as well as LL-37, which belongs to the cathelicidin family of antibacterial peptides, are prominent examples of bactericidal peptides derived through such a cleavage mechanism (15,22,34). In addition, analysis of the amino acid sequence of IL-8 revealed similarities with Hp (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) derived from the gastric pathogen Helicobacter pylori, the causative agent of gastritis and peptic ulcers.…”

“…This group of cecropin-like antibacterial peptides, first identified as the principal component of the humoral immune system of insects and later found in a variety of organisms (5), have in common an amphipathic ␣-helix structure which is an important structural feature. This is illustrated by the fact that amino acid replacements that break or stabilize the helical structure will reduce or abolish or increase the antibacterial activity, respectively (5,14,29). The cecropins as well as cecropin-like peptides exercise their antibacterial effect through the formation of pore structures in phospholipid bilayers, leading to depolarization of the membrane of the target microbe (13), an activity for which the ␣-helical structure is decisive (8).…”

Receptor-Dependent and -Independent Immunomodulatory Effects of Phenol-Soluble Modulin Peptides from Staphylococcus aureus on Human Neutrophils Are Abrogated through Peptide Inactivation by Reactive Oxygen Species

“…Release of lactate dehydrogenase (LDH) was assayed with a kit from Roche Diagnostics (Mannheim, Germany) according to the description by the manufacturer. Cytotoxicity of PSM␣ peptides on bacterial membranes was assessed with an inhibition zone assay as previously described (22).…”