Development of Novel Promiscuous Anti-Chemokine Peptibodies for Treating Autoimmunity and Inflammation

Chemokines and their receptors play critical roles in the progression of autoimmunity and inflammation. Typically, multiple chemokines are involved in the development of these pathologies. Indeed, targeting single chemokines or chemokine receptors has failed to achieve significant clinical benefits in treating autoimmunity and inflammation. Moreover, the binding of host atypical chemokine receptors to multiple chemokines as well as the binding of chemokine-binding proteins secreted by various pathogens can serve as a strategy for controlling inflammation. In this work, promiscuous chemokine-binding peptides that could bind and inhibit multiple inflammatory chemokines, such as CCL2, CCL5, and CXCL9/10/11, were selected from phage display libraries. These peptides were cloned into human mutated immunoglobulin Fc-protein fusions (peptibodies). The peptibodies BKT120Fc and BKT130Fc inhibited the ability of inflammatory chemokines to induce the adhesion and migration of immune cells. Furthermore, BKT120Fc and BKT130Fc also showed a significant inhibition of disease progression in a variety of animal models for autoimmunity and inflammation. Developing a novel class of antagonists that can control the courses of diseases by selectively blocking multiple chemokines could be a novel way of generating effective therapeutics.

In vitro activity and mode of action of diastereomeric antimicrobial peptides against bacterial clinical isolates

OBJECTIVES

Increasing resistance of pathogenic bacteria to antibiotics is a severe problem in health care and has intensified the search for novel drugs. Cationic antibacterial peptides are the most abundant antibiotics in nature and have been frequently proposed as new anti-infective agents. Here, a group of diastereomeric (containing d- and l-amino acids) peptides is studied regarding their potency against multiply resistant clinical isolates and their modes of action against Gram-positive cocci.

METHODS

MIC determinations and chequerboard titrations followed established procedures. Mode of action studies included killing kinetics and a series of experiments designed to characterize the impact of the diastereomeric peptides on bacterial membranes.

RESULTS

The tested diastereomers displayed high antimicrobial and broad spectrum activity with amphipathic-2D being the most active peptide. Synergic activities were observed with individual strains. Mode of action studies clearly demonstrated that the cytoplasmic membrane is a primary target for the peptides and that membrane disruption constitutes a significant bactericidal activity for the major fraction of a bacterial population. However, depending on the indicator strain, the results also suggest that additional molecular events contribute to the overall activity.

Effect of multiple aliphatic amino acids substitutions on the structure, function, and mode of action of diastereomeric membrane active peptides

The initial stages leading to the binding and functioning of membrane-active polypeptides including hormones, signal sequences, and lytic peptides are mainly governed by electrostatic attraction and hydrophobic partitioning between water and lipid bilayers. Antimicrobial peptides serve as an important model for studying the details of these initial steps. However, a systematic analysis of the contribution of multiple hydrophobic amino acids to these steps have been hindered by the propensity of many peptides to aggregate and become inactivated in solution. To this end, we synthesized a series of model amphipathic all L-amino acid peptides and their diastereomers with the sequence KX(3)KWX(2)KX(2)K, where X = Gly, Ala, Val, Ile, or Leu. The effect of the aliphatic amino acids on the biological activity, binding, structure, membrane localization, and mode of action of these peptides was investigated. Most of the L-amino acid peptides oligomerized and adopted distinct structures in solution and in a membrane mimetic environment. Among this group only the Leu containing peptide was hemolytic and highly active on most bacteria tested. The Val- and Leu-containing peptides were hemolytic but inactive toward most bacteria tested. In contrast, the diastereomeric peptides were monomeric and unstructured in solution, but they adopted distinct structures upon membrane binding. While hemolytic activity was drastically reduced, the spectrum of antibacterial activity was preserved or increased. Importantly, we found a direct correlation with the diastereomers between hydrophobicity and propensity to form a helical/distorted-helix and activity (induced membrane leakage and antibacterial activity), despite the fact that they contained 30% D-amino acids. Furthermore, efficient increase in membrane permeability can proceed through different mechanisms. Specifically, the Leu-containing diastereomeric peptide micellized vesicles and possibly bacterial membranes while the Ile-containing diastereomeric peptide fused model membranes and irregularly disrupted bacterial membranes.

From "carpet" mechanism to de-novo designed diastereomeric cell-selective antimicrobial peptides

Living organisms of all types produce a large repertoire of gene-encoded, net positively charged, antimicrobial peptides as part of their innate immunity to microbial invasion. Despite significant variations in composition, length and secondary structure most antimicrobial peptides are active in micromolar concentrations, suggesting a common general mechanism for their mode of action. Many antimicrobial peptides bind bacterial phospholipid membranes up to a threshold concentration, followed by membrane permeation/disintegration (the "carpet" mechanism). Recent data suggest that the details of the permeation pathways may vary for different peptides and are assigned to different modes of action. Accumulating data reveal that the molecular basis for cell selectivity is the ability of peptides to specifically bind the negatively charged bacterial membrane, as well as their oligomeric state in solution and in the membrane. Based on the "carpet" mechanism and the role of the peptide oligomeric state, a novel group of diastereomeric (containing D- and L-amino acids) antimicrobial peptides were developed. These peptides may serve as promising templates for the future designs of antimicrobial peptides.

The Effect of Cyclization of Magainin 2 and Melittin Analogues on Structure, Function, and Model Membrane Interactions: Implication to Their Mode of Action

The amphipathic alpha-helical structure is a common motif found in membrane binding polypeptides including cell lytic peptides, antimicrobial peptides, hormones, and signal sequences. Numerous studies have been undertaken to understand the driving forces for partitioning of amphipathic alpha-helical peptides into membranes, many of them based on the antimicrobial peptide magainin 2 and the non-cell-selective cytolytic peptide melittin, as paradigms. These studies emphasized the role of linearity in their mode of action. Here we synthesized and compared the structure, biological function, and interaction with model membranes of linear and cyclic analogues of these peptides. Cyclization altered the binding of melittin and magainin analogues to phospholipid membranes. However, at similar bound peptide:lipid molar ratios, both linear and cyclic analogues preserved their high potency to permeate membranes. Furthermore, the cyclic analogues preserved approximately 75% of the helical structure of the linear peptides when bound to membranes. Biological activity studies revealed that the cyclic melittin analogue had increased antibacterial activity but decreased hemolytic activity, whereas the cyclic magainin 2 analogue had a marked decrease in both antibacterial and hemolytic activities. The results indicate that the linearity of the peptides is not essential for the disruption of the target phospholipid membrane, but rather provides the means to reach it. In addition, interfering with the coil-helix transition by cyclization, while maintaining the same sequence of hydrophobic and positively charged amino acids, allows a separated evaluation of the hydrophobic and electrostatic contributions to binding of peptides to membranes.

Mode of action of linear amphipathic alpha-helical antimicrobial peptides

The increasing resistance of bacteria to conventional antibiotics resulted in a strong effort to develop antimicrobial compounds with new mechanisms of action. Antimicrobial peptides seem to be a promising solution to this problem. Many studies aimed at understanding their mode of action were described in the past few years. The most studied group includes the linear, mostly alpha-helical peptides. Although the exact mechanism by which they kill bacteria is not clearly understood, it has been shown that peptide-lipid interactions leading to membrane permeation play a role in their activity. Membrane permeation by amphipathic alpha-helical peptides can proceed via either one of the two mechanisms: (a) transmembrane pore formation via a "barrel-stave" mechanism; and (b) membrane destruction/solubilization via a "carpet-like" mechanism. The purpose of this review is to summarize recent studies aimed at understanding the mode of action of linear alpha-helical antimicrobial peptides. This review, which is focused on magainins, cecropins, and dermaseptins as representatives of the amphipathic alpha-helical antimicrobial peptides, supports the carpet-like rather the barrel-stave mechanism. That these peptides vary with regard to their length, amino acid composition, and next positive charge, but act via a common mechanism, may imply that other linear antimicrobial peptides that share the same properties also share the same mechanism.

Cyclization of a cytolytic amphipathic alpha-helical peptide and its diastereomer: effect on structure, interaction with model membranes, and biological function

The amphipathic alpha-helical structure is considered to be a prerequisite for the lytic activity of a large group of cytolytic peptides. However, despite numerous studies on the contribution of various parameters to their structure and activity, the importance of linearity has not been examined. In the present study we functionally and structurally characterized a linear amphipathic alpha-helical peptide (wt peptide), its diastereomer, and cyclic analogues of both. Using analogues with the same sequence of hydrophobic and positively charged amino acids, but with different propensities to form a helical structure, we were able to examine the contribution of linearity to helix formation, bilogical function, and membrane binding and permeation. Importantly, we found that cyclization increases the selectivity between bacteria and human erythrocytes by substantially reducing the hemolytic activity of the cyclic peptides compared with the linear peptides. Moreover, whereas the wt peptide was highly active toward gram(+) bacteria, its cyclic counterpart is active toward both gram(+) and gram(-) bacteria. These findings are correlated with an impaired ability of the cyclic analogues to bind and permeate zwitterionic phospholipid membranes compared with their linear counterparts and an increase in the binding and permeating activity of the cyclic wt peptide toward negatively charged membranes. Furthermore, cyclization abolished the oligomerization of the linear wt peptide in solution and in SDS, suggesting an additional factor that may account for the difference in the spectrum of antibacterial activity between the linear and the cyclic wt peptides. Interestingly, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy revealed that, despite cyclization and incorporation of 33% D-amino acids along the peptide backbone, the membrane environment can impose a predominantly helical structure on the peptides, which is required for their bilogical function. Overall, our results indicate that linearity is not a prerequisite for lytic activity of amphipathic alpha-helical peptides but rather affects the selectivity between gram(+) and gram(-) bacteria and between mammalian cells and bacteria. In addition, the combination of incorporating of D-amino acids into lytic peptides and their cyclization open the way for developing a new group of antimicrobial peptides with improved properties for treating infectious diseases.

Androctonin, a hydrophilic disulphide-bridged non-haemolytic anti-microbial peptide: a plausible mode of action

Androctonin is a 25-residue non-haemolytic anti-microbial peptide isolated from the scorpion Androctonus australis and contains two disulphide bridges. Androctonin is different from known native anti-microbial peptides, being a relatively hydrophilic and non-amphipathic molecule. This raises the possibility that the target of androctonin might not be the bacterial membrane, shown to be a target for most amphipathic lytic peptides. To shed light on its mode of action on bacteria and its non-haemolytic activity, we synthesized androctonin, its fluorescent derivatives and its all-D-amino acid enantiomer. The enantiomer preserved high activity, suggesting a lipid-peptide interaction between androctonin and bacterial membranes. In Gram-positive and (at higher concentrations) Gram-negative bacteria, androctonin induced an immediate perturbation of the permeability properties of the cytoplasmic membrane of the bacterial energetic state, concomitant with perturbation of the morphology of the cell envelope as revealed by electron microscopy. Androctonin binds only to negatively charged lipid vesicles and induces the leakage of markers at high concentrations and with a slow kinetics, in contrast with amphipathic alpha-helical anti-microbial peptides that bind and permeate negatively charged vesicles, and to a smaller extent also zwitterionic ones. This might explain the selective lytic activity of androctonin towards bacteria but not red blood cells. Polarized attenuated total reflection-Fourier transform infrared spectroscopy revealed that androctonin adopts a beta-sheet structure in membranes and did not affect the lipid acyl chain order, which supports a detergent-like effect. The small size of androctonin, its hydrophilic character and its physicochemical properties are favourable features for its potential application as a replacement for commercially available antibiotics to which bacteria have developed resistance.

Structure and organization of hemolytic and nonhemolytic diastereomers of antimicrobial peptides in membranes

Recently, we reported on a new group of diastereomers of short-model peptides (12 amino acids long) composed of leucine and lysine with varying ratios, possessing several properties that make them potentially better than native or de novo-designed all L-amino acid antimicrobial peptides. Preliminary studies have revealed that modulating the hydrophobicity and positive charges of these diastereomers is sufficient to confer antibacterial activity and cell selectivity. However, the relationship between their biological function, structure, and mode of action was not investigated. Here we synthesized and investigated three types of linear model diastereomers (12 amino acids long) with varying lysine:leucine (or tryptophan) ratios (i.e., K(3)L(8)W, K(5)L(6)W, and K(7)L(4)W), which confer different levels of lytic activities. For each K:L ratio, tryptophan was introduced in the middle or the N- or C-terminus of the peptides, as an intrinsic fluorescent probe. Only the hemolytic peptide K(3)L(8)W binds to both negatively charged and zwitterionic phospholipid membranes. K(5)L(6)W and K(7)L(4)W bind similarly, but only to negatively charged membranes, despite the fact that K(5)L(6)W is substantially more lytic to bacteria than K(7)L(4)W. Interestingly, although K(3)L(8)W contains 33% D-amino acids, ATR-FTIR spectroscopy revealed a structure of approximately 90% alpha-helix in both types of membranes. In addition, K(5)L(6)W contains approximately 40% 3(10)-helix and K(7)L(4)W is predominantly a random coil in membranes. Polarized ATR-FTIR and tryptophan-quenching experiments, using brominated phospholipids, revealed a similar depth of penetration and an orientation that was parallel to the membrane surface for all the peptides, but with K(3)L(8)W affecting the lipid order more than the others. The results provide insight into the mode of action of this group of diastereomeric peptides, and the effect of hydrophobicity and positive charges on their membrane structure, function, and cell selectivity. Moreover, this research should assist in the development of suitable diastereomeric peptide antibiotics for therapeutic use that would overcome the problem the increasing resistance of bacteria to conventional antibiotics.

2D-NMR and ATR-FTIR study of the structure of a cell-selective diastereomer of melittin and its orientation in phospholipids

Melittin, a 26 residue, non-cell-selective cytolytic peptide, is the major component of the venom of the honey bee Apis mellifera. In a previous study, a diastereomer ([D]-V(5,8),I(17),K(21)-melittin, D-amino acids at positions V(5,8),I(17),K(21)) of melittin was synthesized and its function was investigated [Oren, Z., and Shai, Y. (1997) Biochemistry 36, 1826-1835]. [D]-V(5,8),I(17),K(21)-melittin lost its cytotoxic effects on mammalian cells; however, it retained antibacterial activity. Furthermore, [D]-V(5,8),I(17),K(21)-melittin binds strongly and destabilizes only negatively charged phospholipid vesicles, in contrast to native melittin, which binds strongly also zwitterionic phospholipids. To understand the differences in the properties of melittin and its diastereomer, 2D-NMR experiments were carried out with [D]-V(5,8),I(17),K(21)-melittin, and polarized attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy experiments were done with both melittin and [D]-V(5,8), I(17),K(21)-melittin. The structure of the diastereomer was characterized by NMR in water, as well as in three different membrane-mimicking environment, 40% 2,2,2-trifluoroethanol (TFE)/water, methanol, and dodecylphosphocholine/phosphatidylglycerol (DPC/DMPG) micelles. The NMR data revealed an amphipathic alpha-helix only in the C-terminal region of the diastereomer in TFE/water and methanol solutions and in DPC/DMPG micelles. ATR-FTIR experiments revealed that melittin and [D]-V(5,8),I(17),K(21)-melittin are oriented parallel to the membrane surface. This study indicates the role of secondary structure formation in selective cytolytic activity of [D]-V(5,8), I(17),K(21)-melittin. While the N-terminal helical structure is not required for the cytolytic activity toward negatively charged membranes and bacterial cells, it appears to be a crucial structural element for binding and insertion into zwitterionic membranes and for hemolytic activity.

Structure and organization of the human antimicrobial peptide LL-37 in phospholipid membranes: relevance to the molecular basis for its non-cell-selective activity

The antimicrobial peptide LL-37 belongs to the cathelicidin family and is the first amphipathic alpha-helical peptide isolated from human. LL-37 is considered to play an important role in the first line of defence against local infection and systemic invasion of pathogens at sites of inflammation and wounds. Understanding its mode of action may assist in the development of antimicrobial agents mimicking those of the human immune system. In vitro studies revealed that LL-37 is cytotoxic to both bacterial and normal eukaryotic cells. To gain insight into the mechanism of its non-cell-selective cytotoxicity, we synthesized and structurally and functionally characterized LL-37, its N-terminal truncated form FF-33, and their fluorescent derivatives (which retained structure and activity). The results showed several differences, between LL-37 and other native antimicrobial peptides, that may shed light on its in vivo activities. Most interestingly, LL-37 exists in equilibrium between monomers and oligomers in solution at very low concentrations. Also, it is significantly resistant to proteolytic degradation in solution, and when bound to both zwitterionic (mimicking mammalian membranes) and negatively charged membranes (mimicking bacterial membranes). The results also showed a role for the N-terminus in proteolytic resistance and haemolytic activity, but not in antimicrobial activity. The LL-37 mode of action with negatively charged membranes suggests a detergent-like effect via a 'carpet-like' mechanism. However, the ability of LL-37 to oligomerize in zwitterionic membranes might suggest the formation of a transmembrane pore in normal eukaryotic cells. To examine this possibility we used polarized attenuated total reflectance Fourier-transform infrared spectroscopy and found that the peptide is predominantly alpha-helical and oriented nearly parallel with the surface of zwitterionic-lipid membranes. This result does not support the channel-forming hypothesis, but rather it supports the detergent-like effect.

A comparative study on the structure and function of a cytolytic alpha-helical peptide and its antimicrobial beta-sheet diastereomer

Antimicrobial peptides which adopt mainly or only beta-sheet structures have two or more disulfide bonds stabilizing their structure. The disruption of the disulfide bonds results in most cases in a large decrease in their antimicrobial activity. In the present study we examined the effect of d-amino acids incorporation on the structure and function of a cytolytic alpha-helical peptide which acts on erythrocytes and bacteria. The influence of a single or double d-amino acid replacement in alpha-helical peptides on their structure was reported previously in 50% 2,2,2, trifluoroethanol/water [Krause et al. (1995) Anal. Chem. 67, 252-258]. Here we used Attenuated Total Reflectance Fourier-Transform Infrared (ATR-FTIR) spectroscopy and found that the predominant structure of the wild-type peptide is alpha-helix in phospholipid membranes, whereas the structure of the diastereomer is beta-sheet. However, the linear, beta-sheet diastereomer preserved its cytolytic activity on bacteria but not on erythrocytes. Previous studies have shown that the ability of antimicrobial peptides to lyse bacteria but not normal mammalian cells correlated with their ability to disintegrate preferentially negatively charged, but not zwitterionic phospholipid membranes. In contrast, the diastereomer described here disrupts zwitterionic and negatively charged vesicles with similar potencies to those of the hemolytic wild-type peptide. Interestingly, whereas addition of a positive charge to the N-terminus of the wild-type peptide (which caused a minor effect on its structure) increased activity only towards some of the bacteria tested, similar modification in the diastereomer increased activity towards all of them. Furthermore, the modified wild-type peptide preserved its potency to destabilize zwitterionic and negatively charged vesicles, whereas the modified diastereomer had a reduced potency on zwitterionic vesicles but increased potency on negatively charged vesicles. Overall our results suggest that this new class of antimicrobial diastereomeric peptides bind to the membrane in 'carpet-like' manner followed by membrane disruption and breakdown, rather than forming a transmembrane pore which interfere with the bacteria potential. These studies also open a way to design new broad-spectrum antibacterial peptides.

A repertoire of novel antibacterial diastereomeric peptides with selective cytolytic activity

The increase in infectious diseases and bacterial resistance to antibiotics has resulted in intensive studies focusing on the use of linear, alpha-helical, cytolytic peptides from insects and mammals as potential drugs for new target sites in bacteria. Recent studies with diastereomers of the highly potent cytolytic peptides, pardaxin and melittin, indicate that alpha-helical structure is required for mammalian cells lysis but is not necessary for antibacterial activity. Thus, hydrophobicity and net positive charge of the polypeptide might confer selective antibacterial lytic activity. To test this hypothesis, a series of diastereomeric model peptides (12 amino acids long) composed of varying ratios of leucine and lysine were synthesized, and their structure and biological function were investigated. Peptide length and the position of D-amino acids were such that short peptides with stretches of only 1-3 consecutive L-amino acids that cannot form an alpha-helical structure were constructed. Circular dichroism spectroscopy showed that the peptides do not retain any detectable secondary structure in a hydrophobic environment. This enabled examination of the sole effect of hydrophobicity and positive charge on activity. The data reveal that modulating hydrophobicity and positive charge is sufficient to confer antibacterial activity and cell selectivity. A highly hydrophobic diastereomer that permeated both zwitterionic and negatively charged phospholipid vesicles, lysed eukaryotic and prokaryotic cells. In contrast, a highly positively charged diastereomer that only permeated slightly negatively charged phospholipid vesicles had low antibacterial activity and could not lyse eukaryotic cells. In the boundary between high hydrophobicity and high positive charge, the diastereomers acquired selective and potent antibacterial activity. Furthermore, they were completely resistant to human serum inactivation, which dramatically reduces the activity of native antibacterial peptides. In addition, a strong synergistic effect was observed at nonlethal concentrations of the peptides with the antibiotic tetracycline on resistant bacteria. The results are discussed in terms of proposed mechanisms of antibacterial activity, as well as a new strategy for the design of a repertoire of short, simple, and easily manipulated antibacterial peptides as potential drugs in the treatment of infectious diseases.

Selective lysis of bacteria but not mammalian cells by diastereomers of melittin: structure-function study

Studies on lipid-peptide interactions of cytolytic polypeptides tend to emphasize the importance of the amphipathic alpha-helical structure for their cytolytic activity. In this study, diasetereomers of the bee venom melittin (26 a.a.), a non-cell-selective cytolysin, were synthesized and investigated for their structure and cytolytic activity toward bacteria and mammalian cells. Similarly to the findings with the diastereomers of the less cytolytic peptide pardaxin (33 a.a.) (Shai & Oren. 1996), the melittin diastereomer, lest their alpha-helical structure, which abrogated their hemolytic activity toward human erythrocytes. However, they retained their antibacterial activity and completely lysed both Gram-positive and Gram-negative bacteria, as revealed by transmission electron microscopy. To understand the molecular mechanism underlying this selectivity, binding experiments utilizing the intrinsic tryptophan of melittin, tryptophan quenching experiments using brominated phospholipids, and membrane destabilization studies were done. The data revealed that the melittin diastereomers bound to and destabilized only negatively-charged phospholipid vesicles, in contrast to native melittin, which binds strongly to both negatively-charged and zwitterionic phospholipids. However, the partition coefficient, the depth of penetration into the membrane, and the membrane-permeating activity of the diastereomers with negatively-charged phospholipids were similar to those obtained with melittin. The results obtained do not support the formation of transmembrane pores as the mode of action of the diastereomers, but rather suggest that these peptides bind to the surface of the bacterial membrane, cover it in a "carpet-like" manner, and dissolve it like a detergent. The results presented here together with those obtained with the cytolytic peptide pardaxin suggest that the combination of hydrophobicity and net positive charge may be sufficient in the design of potent diastereomers of antibacterial polypeptides for the treatment of infectious diseases.

A class of highly potent antibacterial peptides derived from pardaxin, a pore-forming peptide isolated from Moses sole fish Pardachirus marmoratus

Pardaxin, a 33-amino-acid pore-forming polypeptide toxin isolated from the Red Sea Moses sole Pardachirus marmoratus, has a helix-hinge-helix structure. This is a common structural motif found both in antibacterial peptides that can act selectively on bacterial membranes (e.g., cecropin), and in cytotoxic peptides that can lyse both mammalian and bacterial cells (e.g., melittin). Herein we show that pardaxin possesses a high antibacterial activity with a significantly reduced hemolytic activity towards human red blood cells (hRBC), compared with melittin. Its potency is comparable to that of other known native antibacterial peptides such as magainin, cecropins and dermaseptins. To determine the structural features responsible for the selective hemolytic and antibacterial activities, and the structural requirements for a high antibacterial activity, 8 truncated and modified pardaxin analogues were synthesized and structurally and functionally characterized. Each peptide was synthesized with a free carboxylate or amino group (i.e., aminated form) at its C-terminus. The aminated form of pardaxin has both high hemolytic and antibacterial activity. A truncated analogue, with 11 amino acids removed from the C-terminal domain, had dramatically reduced hemolytic activity. However, the aminated form of this analogue was significantly more potent that pardaxin against most bacteria tested, suggesting that the C-terminal tail of pardaxin is responsible for non-selective activity against erythrocytes and bacteria. Furthermore, a positive charge added to its N-terminus significantly increased its antibacterial activity and abolished its low hemolytic activity. The 22-amino-acid C-terminal domain and the short 11-amino-acid N-terminal domain were, in their aminated forms, active only against gram-positive bacteria. Secondary-structure determination using circular dichroism spectroscopy revealed that all the aminated analogues had 25-80% more alpha-helical content in 40% CF3CH2OH/water than their non-aminated forms. Using model phospholipid membranes it was found that all the analogues that were less hemolytic but had retained antibacterial activity could permeate acidicly charged phospholipid vesicles better than zwitterionic phospholipid vesicles, a property characteristics of all the native antibacterial peptides tested so far (e.g., cecropins, magainins and dermaseptins). Pardaxin and its analogues therefore represent a new class of antibacterial peptides that can serve as a basis for the design of therapeutic agents. Furthermore, negative-staining electron microscopy revealed that total inhibition of bacterial growth was due to total lysis of the bacterial wall. Therefore, it might be more difficult for bacteria to develop resistance to such a destructive mechanism, compared with the more specific mechanisms of the currently used antibiotics.

Diastereoisomers of cytolysins, a novel class of potent antibacterial peptides

An amphipathic alpha-helical structure is considered to be a prerequisite for the lytic activity of most short linear cytolytic polypeptides that act on both mammalian cells and bacteria. This structure allows them also to exert diverse pathological and pharmacological effects, presumably by mimicking protein components that are involved in membrane-related events. In this study D-amino acid-incorporated analogues (diastereomers) of the cytolysin pardaxin, which is active against mammalian cells and bacteria, were synthesized and structurally and functionally characterized. We demonstrate that the diastereomers do not retain the alpha-helical structure, which in turn abolishes their cytotoxic effects on mammalian cells. However, they retain a high antibacterial activity, which is expressed in a complete lysis of the bacteria, as revealed by negative staining electron microscopy. The disruption of the alpha-helical structure should prevent the diastereomer analogues from permeating the bacterial wall by forming transmembrane pores but rather by dissolving the membrane as a detergent. These findings open the way for a new strategy in developing a novel class of highly potent antibacterial polypeptides for the treatment of infectious diseases, due to the increasing resistance of bacteria to the available antibacterial drugs.

Major depressives' and dysthmics' performance on the Wisconsin Card Sorting Test

Despite awareness that depression may affect performance on commonly used neuropsychological tests, little research has been conducted on the relative impact of severity and type of depression on higher problem-solving ability. Major depressives (n = 13), dysthymics (n = 17), and non-psychiatric comparison subjects (n = 18) were administered the Wisconsin Card Sorting Test (WCST). Although diagnostic category was related only marginally to some WCST measures after controlling for intellectual function, depressive symptom severity emerged as an independent predictor of Total Errors, Perseverative Responses, and Failure to Maintain Set. These findings lend support to the suggestion that neuropsychological test batteries should include assessment for depression and suggest that even relatively mild depression may affect WCST scores.