Cathelicidin-derived Trp/Pro-rich antimicrobial peptides with lysine peptoid residue (Nlys): therapeutic index and plausible mode of action.

Recently, we designed a novel cell-selective antimicrobial peptide (TPk) with intracellular mode of action from Pro --> Nlys (Lys peptoid residue) substitution in a noncell-selective cathelicidin-derived Trp/Pro-rich antimicrobial peptide, tritrpticin-amide (TP; VRRFPWWWPFLRR-NH(2)) (Biochemistry 2006; 45: 13007-13017). In this study, to elucidate the effect of Pro --> Nlys substitution on therapeutic index and mode of action of other noncell-selective cathelicidin-derived Trp/Pro-rich antimicrobial peptides and develop novel short antimicrobial peptides with high cell selectivity/therapeutic index, we synthesized Nlys-substituted antimicrobial peptides, TPk, STPk and INk, in which all proline residues of TP, symmetric TP-analogue (STP; KKFPWWWPFKK-NH(2)) and indolicidin (IN; ILPWKWPWWPWRR-NH(2)) were replaced by Nlys, respectively. Compared to parent Pro-containing peptides (TP, STP and IN), Nlys substituted peptides (TPk, STPk and Ink) had 4- to 26-fold higher cell selectivity/therapeutic index. Parent Pro-containing peptides induced a significant depolarization of the cytoplasmic membrane of intact Staphylococcus aureus at their MIC, whereas Nlys-substituted antimicrobial peptides did not cause visible membrane depolarization at their MIC. These results suggest that the antibacterial action of Nlys-substituted peptides is probably not due to the disruption of bacterial cytoplasmic membranes but the inhibition of intracellular components. Taken together, our results showed that Pro --> Nlys substitution in other noncell-selective Trp/Pro-rich antimicrobial peptides such as STP and IN as well as TP can improve the cell selectivity/therapeutic index and change the mode of antibacterial action from membrane-disrupting to intracellular targeting. In conclusion, our findings suggested that Pro --> Nlys substitution in noncell-selective Trp/Pro-rich antimicrobial peptides is a promising method to develop cell-selective antimicrobial peptides with intracellular target mechanism.     

Physical behavior of KR-12 peptide on solid surfaces and Langmuir-Blodgett lipid films: Complementary approaches to its antimicrobial mode against S. aureus

Biophysical characterization of antimicrobial peptides helps to understand the mechanistic aspects of their action. The physical behavior of the KR-12 antimicrobial peptide (e.g. orientation and changes in secondary structure), was analyzed after interactions with a Staphylococcus aureus membrane model and solid surfaces. We performed antimicrobial tests using Gram-positive S. aureus (ATCC 25923) bacteria. Moreover, Langmuir-Blodgett experiments showed that the synthetic peptide can disturb the lipidic membrane at a concentration lower than the Minimum Inhibitory Concentration, thus confirming that KR-12/lipid interactions are involved. Partially- and fully-deactivated KR-12 hybrid samples were obtained by physisorption and covalent immobilization in chitosan/silica and glyoxal-rich solid supports. The correlation of Langmuir-Blodgett data with the α-helix formation, followed by FTIR-ATR in a frozen-like state, and the antimicrobial activity showed the importance of these interactions and conformation changes on the first step action mode of this peptide. This is the first time that material science (immobilization in solid surfaces assisted by FTIR-ATR analysis in frozen-like state) and physical (Langmuir-Blodgett/Schaefer) approaches are combined for exploring mechanistic aspects of the primary action mode of the KR-12 antimicrobial peptide against S. aureus.     

The importance of bacterial membrane composition in the structure and function of aurein 2.2 and selected variants

For cationic antimicrobial peptides to become useful therapeutic agents, it is important to understand their mechanism of action. To obtain high resolution data, this involves studying the structure and membrane interaction of these peptides in tractable model bacterial membranes rather than directly utilizing more complex bacterial surfaces. A number of lipid mixtures have been used as bacterial mimetics, including a range of lipid headgroups, and different ratios of neutral to negatively charged headgroups. Here we examine how the structure and membrane interaction of aurein 2.2 and some of its variants depend on the choice of lipids, and how these models correlate with activity data in intact bacteria (MICs, membrane depolarization). Specifically, we investigated the structure and membrane interaction of aurein 2.2 and aurein 2.3 in 1:1 cardiolipin/1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (CL/POPG) (mol/mol), as an alternative to 1:1 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine(POPC)/POPG and a potential model for Gram positive bacteria such as S. aureus. The structure and membrane interaction of aurein 2.2, aurein 2.3, and five variants of aurein 2.2 were also investigated in 1:1 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE)/POPG (mol/mol) lipids as a possible model for other Gram positive bacteria, such as Bacillus cereus. Solution circular dichroism (CD) results demonstrated that the aurein peptides adopted α-helical structure in all lipid membranes examined, but demonstrated a greater helical content in the presence of POPE/POPG membranes. Oriented CD and 31P NMR results showed that the aurein peptides had similar membrane insertion profiles and headgroup disordering effects on POPC/POPG and CL/POPG bilayers, but demonstrated reduced membrane insertion and decreased headgroup disordering on mixing with POPE/POPG bilayers at low peptide concentrations. Since the aurein peptides behaved very differently in POPE/POPG membrane, minimal inhibitory concentrations (MICs) of the aurein peptides in B. cereus strain C737 were determined. The MIC results indicated that all aurein peptides are significantly less active against B. cereus than against S. aureus and S. epidermidis. Overall, the data suggest that it is important to use a relevant model for bacterial membranes to gain insight into the mode of action of a given antimicrobial peptide in specific bacteria.     

Synthesis of bioinorganic antimicrobial peptide nanoparticles with potential therapeutic properties

Amphiphilicity and cationicity are properties shared between antimicrobial peptides and proteins that catalyze biomineralization reactions. Merging these two functionalities, we demonstrate a reaction where a cationic antimicrobial peptide catalyzes self-biomineralization within inorganic matrices. The resultant antimicrobial peptide nanoparticles retain biocidal activity, protect the peptide from proteolytic degradation, and facilitate a continuous release of the antibiotic over time. Taken together, these properties demonstrate the therapeutic potential of self-synthesizing biomaterials that retain the biocidal properties of antimicrobial peptides.     

Structural requirements for cellular uptake and antisense activity of peptide nucleic acids conjugated with various peptides

Peptide nucleic acids (PNAs) have shown great promise as potential antisense drugs; however, poor cellular delivery limits their applications. Improved delivery into mammalian cells and enhanced biological activity of PNAs have been achieved by coupling to cell-penetrating peptides (CPPs). Structural requirements for the shuttling ability of these peptides as well as structural properties of the conjugates such as the linker type and peptide position remained controversial, so far. In the present study an 18mer PNA targeted to the cryptic splice site of a mutated beta-globin intron 2, which had been inserted into a luciferase reporter gene coding sequence, was coupled to various peptides. As the peptide lead we used the cell-penetrating alpha-helical amphipathic peptide KLAL KLAL KAL KAAL KLA-NH2 [model amphipathic peptide (MAP)] which was varied with respect to charge and structure-forming properties. Furthermore, the linkage and the localization of the attached peptide (C- vs N-terminal) were modified. Positive charge as well as helicity and amphipathicity of the KLA peptide was all required for efficient dose-dependent correction of aberrant splicing. The highest antisense effect was reached within 4 h without any transfection agent. Stably linked conjugates were also efficient in correction of aberrant splicing, suggesting that a cleavable disulfide bond between CPP and PNA is clearly not essential. Moreover, the placement of the attached peptide turned out to be crucial for attaining antisense activity. Coadministration of endosome disrupting agents such as chloroquine or Ca2+ significantly increased the splicing correction efficiency of some conjugates, indicating the predominant portion to be sequestered in vesicular compartments.     

Roles of hydrophobicity and charge distribution of cationic antimicrobial peptides in peptide-membrane interactions

Cationic antimicrobial peptides (CAPs) occur as important innate immunity agents in many organisms, including humans, and offer a viable alternative to conventional antibiotics, as they physically disrupt the bacterial membranes, leading to membrane lysis and eventually cell death. In this work, we studied the biophysical and microbiological characteristics of designed CAPs varying in hydrophobicity levels and charge distributions by a variety of biophysical and biochemical approaches, including in-tandem atomic force microscopy, attenuated total reflection-FTIR, CD spectroscopy, and SDS-PAGE. Peptide structural properties were correlated with their membrane-disruptive abilities and antimicrobial activities. In bacterial lipid model membranes, a time-dependent increase in aggregated β-strand-type structure in CAPs with relatively high hydrophobicity (such as KKKKKKALFALWLAFLA-NH(2)) was essentially absent in CAPs with lower hydrophobicity (such as KKKKKKAAFAAWAAFAA-NH(2)). Redistribution of positive charges by placing three Lys residues at both termini while maintaining identical sequences minimized self-aggregation above the dimer level. Peptides containing four Leu residues were destructive to mammalian model membranes, whereas those with corresponding Ala residues were not. This finding was mirrored in hemolysis studies in human erythrocytes, where Ala-only peptides displayed virtually no hemolysis up to 320 μM, but the four-Leu peptides induced 40-80% hemolysis at the same concentration range. All peptides studied displayed strong antimicrobial activity against Pseudomonas aeruginosa (minimum inhibitory concentrations of 4-32 μM). The overall findings suggest optimum routes to balancing peptide hydrophobicity and charge distribution that allow efficient penetration and disruption of the bacterial membranes without damage to mammalian (host) membranes.     

Lipid-induced conformation and lipid-binding properties of cytolytic and antimicrobial peptides: determination and biological specificity

While antimicrobial and cytolytic peptides exert their effects on cells largely by interacting with the lipid bilayers of their membranes, the influence of the cell membrane lipid composition on the specificity of these peptides towards a given organism is not yet understood. The lack of experimental model systems that mimic the complexity of natural cell membranes has hampered efforts to establish a direct correlation between the induced conformation of these peptides upon binding to cell membranes and their biological specificities. Nevertheless, studies using model membranes reconstituted from lipids and a few membrane-associated proteins, combined with spectroscopic techniques (i.e. circular dichroism, fluorescence spectroscopy, Fourier transform infra red spectroscopy, etc.), have provided information on specific structure-function relationships of peptide-membrane interactions at the molecular level. Reversed phase-high performance chromatography (RP-HPLC) and surface plasmon resonance (SPR) are emerging techniques for the study of the dynamics of the interactions between cytolytic and antimicrobial peptides and lipid surfaces. Thus, the immobilization of lipid moieties onto RP-HPLC sorbent now allows the investigation of peptide conformational transition upon interaction with membrane surfaces, while SPR allows the observation of the time course of peptide binding to membrane surfaces. Such studies have clearly demonstrated the complexity of peptide-membrane interactions in terms of the mutual changes in peptide binding, conformation, orientation, and lipid organization, and have, to a certain extent, allowed correlations to be drawn between peptide conformational properties and lytic activity.     

Mechanism of interaction of different classes of cationic antimicrobial peptides with planar bilayers and with the cytoplasmic membrane of Escherichia coli.

Antimicrobial cationic peptides are prevalent throughout nature as part of the intrinsic defenses of most organisms, and have been proposed as a blueprint for the design of novel antimicrobial agents. They are known to interact with membranes, and it has been frequently proposed that this represents their antibacterial target. To see if this was a general mechanism of action, we studied the interaction, with model membranes and the cytoplasmic membrane of Escherichia coli, of 12 peptides representing all 4 structural classes of antimicrobial peptides. Planar lipid bilayer studies indicated that there was considerable variance in the interactions of the peptides with model phospholipid membranes, but generally both high concentrations of peptide and high transmembrane voltages (usually -180 mV) were required to observe conductance events (channels). The channels observed for most peptides varied widely in magnitude and duration. An assay was developed to measure the interaction with the Escherichia coli cytoplasmic membrane employing the membrane potential sensitive dye 3,5-dipropylthiacarbocyanine in the outer membrane barrier-defective E. coli strain DC2. It was demonstrated that individual peptides varied widely in their ability to depolarize the cytoplasmic membrane potential of E. coli, with certain peptides such as the loop peptide bactenecin and the alpha-helical peptide CP26 being unable to cause depolarization at the minimal inhibitory concentration (MIC), and others like gramicidin S causing maximal depolarization below the MIC. We discuss the mechanism of interaction with the cytoplasmic membrane in terms of the model of Matsuzaki et al. [(1998) Biochemistry 37, 15144-15153] and the possibility that the cytoplasmic membrane is not the target for some or even most cationic antimicrobial peptides.     

Cationic antimicrobial peptides disrupt the Streptococcus pyogenes ExPortal

Although they possess a well‐characterized ability to porate the bacterial membrane, emerging research suggests that cationic antimicrobial peptides (CAPs) can influence pathogen behaviour at levels that are sublethal. In this study, we investigated the interaction of polymyxin B and human neutrophil peptide (HNP‐1) with the human pathogen Streptococcus pyogenes. At sublethal concentrations, these CAPs preferentially targeted the ExPortal, a unique microdomain of the S. pyogenes membrane, specialized for protein secretion and processing. A consequence of this interaction was the disruption of ExPortal organization and a redistribution of ExPortal components into the peripheral membrane. Redistribution was associated with inhibition of secretion of certain toxins, including the SpeB cysteine protease and the streptolysin O (SLO) cytolysin, but not SIC, a protein that protects S. pyogenes from CAPs. These data suggest a novel function for CAPs in targeting the ExPortal and interfering with secretion of factors required for infection and survival. This mechanism may prove valuable for the design of new types of antimicrobial agents to combat the emergence of antibiotic‐resistant pathogens.     

High-throughput generation of small antibacterial peptides with improved activity

Cationic antimicrobial peptides are able to kill a broad variety of Gram-negative and Gram positive bacteria and thus are good candidates for a new generation of antibiotics to treat multidrug-resistant bacteria. Here we describe a high-throughput method to screen large numbers of peptides for improved antimicrobial activity. The method relies on peptide synthesis on a cellulose support and a Pseudomonas aeruginosa strain that constitutively expresses bacterial luciferase. A complete substitution library of 12-amino-acid peptides based on a linearized variant (RLARIVVIRVAR-NH(2)) of the bovine peptide bactenecin was screened and used to determine which substitutions at each position of the peptide chain improved activity. By combining the most favorable substitutions, we designed optimized 12-mer peptides showing broad spectrum activities with minimal inhibitory concentrations (MIC) as low as 0.5 microg/ml against Escherichia coli. Similarly, we generated an 8-mer substituted peptide that showed broad spectrum activity, with an MIC of 2 microg/ml, against E. coli and Staphylococcus aureus.     

Kinetic microplate assay for determining immobilized antimicrobial peptide activity

Antimicrobial peptide immobilization onto surfaces is of great interest, although characterization of activity can be problematic. The kinetic microplate method described here determines the minimum bactericidal concentration (MBC) of immobilized antimicrobial peptides through a combination and modification of traditional solution assays, overcoming the difficulties of working with a solid substrate. The technique enables rapid, accurate evaluation of immobilized peptide lytic behavior, elucidating both dose- and time-dependent activity at multiple concentrations. Furthermore, the method yields information regarding sublethal concentrations not realized in the traditional assays.     

Helix induction in antimicrobial peptides by alginate in biofilms

Bacterial exopolysaccharides provide protection against phagocytosis, opsonization, and dehydration and act as a major structural component of the extracellular matrix in biofilms. They contribute to biofilm-related resistance by acting as a diffusion barrier to positively charged antimicrobial agents including cationic antimicrobial peptides (CAPs). We previously created novel CAPs consisting of a nonamphipathic hydrophobic core flanked by Lys residues and containing a Trp residue in the hydrophobic segment as a fluorescent probe. Peptides of this type above a specific hydrophobicity threshold insert spontaneously into membranes and have antimicrobial activity against Gram-positive and Gram-negative bacteria at micromolar concentrations. Here we show that alginate, a polymer of beta-d-mannuronate and alpha-l-guluronate secreted by the cystic fibrosis pathogen Pseudomonas aeruginosa, induces an alpha-helical conformation detected by circular dichroism spectroscopy and blue shifts in Trp fluorescence maxima in peptides above the hydrophobicity threshold, changes typically observed upon association of such peptides with nonpolar (membrane) environments. Parallel effects were observed in the archetypical CAPs magainin II amide and cecropin P1. Fluorescence resonance energy transfer studies indicated that alginate induces peptide-peptide association only in peptides above the hydrophobicity threshold, suggesting that the hydrophilic alginate polymer behaves as an "auxiliary membrane" for the bacteria, demonstrating a unique protective role for biofilm matrices against CAPs.     

Amphiphilic cationic peptides mediate cell adhesion to plastic surfaces

Four amphiphilic peptides, each with net charges of +2 or more at neutrality and molecular weights under 4 kilodaltons, were found to mediate the adhesion of normal rat kidney fibroblasts to polystyrene surfaces. Two of these peptides, a model for calcitonin (peptide 1, MCT) and melittin (peptide 2, MEL), form amphiphilic alpha-helical structures at aqueous/nonpolar interfaces. The other two, a luteinizing hormone-releasing hormone model (peptide 3, LHM) and a platelet factor model (peptide 4, MPF) form beta-strand structures in amphiphilic environments. Although it contains only 10 residues, LHM mediated adhesion to surfaces coated with solutions containing as little as 10 pmoles/ml of peptide. All four of these peptides were capable of forming monolayers at air-buffer interfaces with collapse pressures greater than 20 dynes/cm. None of these four peptides contains the tetrapeptide sequence Arg-Gly-Asp-Ser, which has been associated with fibronectin-mediated cell adhesion. Ten polypeptides that also lacked the sequence Arg-Gly-Asp-Ser but were nonamphiphilic and/or had net charges less than +2 at neutrality were all incapable of mediating cell adhesion (Pierschbacher and Ruoslahti, 1984). The morphologies of NRK cells spread on polystyrene coated with peptide LHM resemble the morphologies on fibronectin-coated surfaces, whereas cells spread on surfaces coated with MCT or MEL exhibit strikingly different morphologies. The adhesiveness of MCT, MEL, LHM, and MPF implies that many amphiphilic cationic peptides could prove useful as well defined adhesive substrata for cell culture and for studies of the mechanism of cell adhesion.     

Not only the nature of peptide but also the characteristics of cell membrane determine the antimicrobial mechanism of a peptide.

The mechanisms of antimicrobial actions of magainin 2, buforin II and poly L-lysine against various Escherichia coli strains were studied. Poly L-lysine inhibited BL21, AD 434 and GroE+/DnaK+ growth without lysing the cell. Magainin 2 had a pore-forming activity on BL 21 and AD 434 membrane but could not inhibit the GroE+/DnaK+ growth in a nutrient-rich medium. Buforin II, which killed BL21 and AD 434 without cell membrane damage, lysed GroE+/DnaK+ to death. Once they were introduced into the cell by electroporation, all three peptides were able to inhibit cell growth at concentrations of 10 times lower than their MICs. These results indicate that the nature of the peptide and also the characteristics of the cell membrane determine the antimicrobial actions of a peptide.     

Antimicrobial Properties and Membrane-Active Mechanism of a Potential α-Helical Antimicrobial Derived from Cathelicidin PMAP-36

Antimicrobial peptides (AMPs), which present in the non-specific immune system of organism, are amongst the most promising candidates for the development of novel antimicrobials. The modification of naturally occurring AMPs based on their residue composition and distribution is a simple and effective strategy for optimization of known AMPs. In this study, a series of truncated and residue-substituted derivatives of antimicrobial peptide PMAP-36 were designed and synthesized. The 24-residue truncated peptide, GI24, displayed antimicrobial activity comparable to the mother peptide PMAP-36 with MICs ranging from 1 to 4 µM, which is lower than the MICs of bee venom melittin. Although GI24 displayed high antimicrobial activity, its hemolytic activity was much lower than melittin, suggesting that GI24 have optimal cell selectivity. In addition, the crucial site of GI24 was identified through single site-mutation. An amino acid with high hydrophobicity at position 23 played an important role in guaranteeing the high antimicrobial activity of GI24. Then, lipid vesicles and whole bacteria were employed to investigate the membrane-active mechanisms. Membrane-simulating experiments showed that GI24 interacted strongly with negatively charged phospholipids and weakly with zwitterionic phospholipids, which corresponded well with the data of its biological activities. Membrane permeabilization and flow cytometry provide the evidence that GI24 killed microbial cells by permeabilizing the cell membrane and damaging membrane integrity. GI24 resulted in greater cell morphological changes and visible pores on cell membrane as determined using scanning electron microscopy (SEM) and transmission electron microscope (TEM). Taken together, the peptide GI24 may provide a promising antimicrobial agent for therapeutic applications against the frequently-encountered bacteria.     

Antimicrobial activity of two peptides casecidin 15 and 17, found naturally in bovine colostrum

Aims:  To isolate and characterize peptides from bovine colostrum with antimicrobial activity.
Methods and Results:  Three peptides were purified from fresh colostrum by a range of chromatographic methods using antimicrobial activity against Escherichia coli DH5α to screen for the most active fractions. Two peptides, with antimicrobial activity, casecidin 17 and casecidin 15, were identical to sequences in the C-terminal of bovine β-casein (YQEPVLGPVRGPFPIIV and YQEPVLGPVRGPFPI) and had corresponding molecular masses of 1881·00 and 1669·06 Da, respectively. The third peptide was the known peptide isracidin which has a mass of 2763·80 Da and sequence of RPKHPIKHQGLPQEVLNENLLRF. Casecidin 17 and casecidin 15 had identical minimal inhibition concentrations (MICs) against E. coli DPC6053 of 0·4 mg ml⁻¹. Structural modelling suggested amphiphilic structures having identical inhibitory and structural properties. The MIC value of isracidin against E. coli DPC6053 was 0·2 mg ml⁻¹.
Conclusions:  This study shows the presence of three antimicrobial peptides in colostrum which may contribute to a bioprotective role to limit pathogen contamination. Furthermore, the discovery of casecidin 17 and 15 may provide the basis for novel antimicrobial peptide design.
Significance and Impact of the Study:  This is the first study to characterize peptides with antimicrobial activity present in fresh bovine colostrum.     

Membrane interactions of designed cationic antimicrobial peptides: the two thresholds

Novel cationic antimicrobial peptides (CAPs) designed in our lab-typified by sequences such as KKKKKKAAX-AAXAAXAA-NH(2), where X = Phe/Trp-display high antibacterial activity but exhibit little or no hemolytic activity towards human red blood cells even at high doses. To clarify the mechanism of their selectivity for bacterial versus mammalian membranes and to increase our understanding of the relationships between primary sequence and bioactivity, a library of derivatives was prepared by increasing segmental hydrophobicity, in which systematic substitutions of Ala for two, three, or four Leu residues were made. Conformationally constrained dimeric and cyclic derivatives were also synthesized. The peptides were examined for activity against pathogenic bacteria (Pseudomonas aeruginosa), hemolytic activity on human red blood cells, and insertion into models of natural bacterial membranes (containing anionic lipids) and mammalian membranes (containing zwitterionic lipids + cholesterol). Results were compared with corresponding properties of the natural CAPs magainin and cecropin. Using circular dichroism and fluorescence spectroscopy, we found that peptide conformation and membrane insertion were sequence dependent, both upon the number of Leu residues, and upon their positions along the hydrophobic core. Membrane disruption was likely enhanced by the fact that the peptides contain potent dimerization-promoting sequence motifs, as assessed by SDS-PAGE gel analysis. The overall results led us to identify distinctions in the mechanism of actions of these CAPs for disruption of bacterial versus mammalian membranes, the latter dependent on surpassing a "second hydrophobicity threshold" for insertion into zwitterionic membranes.     

The specificity of protection against cationic antimicrobial peptides by lactoferrin binding protein B

A variety of Gram-negative pathogens possess host-specific lactoferrin (Lf) receptors that mediate the acquisition of iron from host Lf. The integral membrane protein component of the receptor, lactoferrin binding protein A specifically binds host Lf and is required for acquisition of iron from Lf. In contrast, the role of the bi-lobed surface lipoprotein, lactoferrin binding protein B (LbpB), in Lf binding and iron acquisition is uncertain. A common feature of LbpBs from most species is the presence of clusters of negatively charged amino acids in the protein’s C-terminal lobe. Recently it has been shown that the negatively charged regions from the Neisseria meningitidis LbpB are responsible for protecting against an 11 amino acid cationic antimicrobial peptide (CAP), lactoferricin (Lfcin), derived from human Lf. In this study we investigated whether the LbpB confers resistance to other CAPs since N. meningitidis is likely to encounter other CAPs from the host. LbpB provided protection against the cathelicidin derived peptide, cathelicidin related antimicrobial peptide (mCRAMP), but did not confer protection against Tritrp 1 or LL37 under our experimental conditions. When tested against a range of rationally designed synthetic peptides, LbpB was shown to protect against IDR-1002 and IDR-0018 but not against HH-2 or HHC10.     

Preparation of LL-37-grafted titanium surfaces with bactericidal activity

Modification of material surfaces aimed at bestowing them with antimicrobial properties is a promising approach in the development of new biomaterials. Antimicrobial peptides (AMPs) are an attractive alternative to conventional antibiotics because of lack of toxicity, inherently high selectivity, and absence of immune response. As the antimicrobial mode of action of the AMP cathelin LL37 is formation of pores and disruption of microbial membrane, the purpose of the present study was to develop and test a method of covalent immobilization of LL37 on titanium surface. The application of a flexible hydrophilic poly(ethylene glycol) spacer and selective N-terminal conjugation of LL37 resulted in a surface peptide layer which was capable of killing bacteria on contact.     

一组人工合成抗菌肽的研究

Cecropin A1是一种从惜古比天蚕(Hyalophora cecropia)中提取的由37个氨基酸组成的一种α-螺旋抗菌肽,其杀菌活性较弱。本文采用了cecropin A1的N端1-8序列KWKLFKKI,另加一段标准的α-螺旋结构序列,然后用一个铰链结构GIG相连,合成了15条抗菌肽。经过试验证明部分含有核心标准螺旋结构的序列,对革兰氏阳性菌和阴性菌的最小抑菌浓度仅是原有cecropin A1抗菌肽的1/100左右。该类抗菌肽有希望进一步开发为新的抗感染药物。该类抗菌肽已经申请专利,专利号为PCT/CN 03/00522。