A potent candicidal peptide designed based on an encrypted peptide from a proteinase inhibitor

Antimicrobial peptides (AMP) represent an alternative in the treatment of fungal infections associated with countless deaths. Here, we report a new AMP, named KWI-19, which was designed based on a peptide encrypted in the sequence of an Inga laurina Kunitz-type inhibitor (ILTI). KWI-19 inhibited the growth of Candida species and acted as a fungicidal agent from 2.5 to 20 μmol L-1, also showing synergistic activity with amphotericin B. Kinetic assays showed that KWI-19 killed Candida tropicalis cells within 60 min. We also report the membrane-associated mechanisms of action of KWI-19 and its interaction with ergosterol. KWI-19 was also characterized as a potent antibiofilm peptide, with activity against C. tropicalis. Finally, non-toxicity was reported against Galleria mellonella larvae, thus strengthening the interest in all the bioactivities mentioned above. This study extends our knowledge on how AMPs can be engineered from peptides encrypted in larger proteins and their potential as candicidal agents.

Hemoglobin Protects Enamel against Intrinsic Enamel Erosive Demineralization

INTRODUCTION

This study investigated the changes in the acquired enamel pellicle (AEP) proteome when this integument is formed in vivo after treatment with sugarcane-derived cystatin (CaneCPI-5), hemoglobin (HB), and a statherin-derived peptide (StN15), or their combination and then exposed to an intrinsic acid challenge. The effectiveness of these treatments in preventing intrinsic erosion was also evaluated.

METHODS

Ten volunteers, after prophylaxis, in 5 crossover phases, rinsed with the following solutions (10 mL, 1 min): control (deionized water-H2O) - group 1, 0.1 mg/mL CaneCPI-5 - group 2, 1.0 mg/mL HB - group 3, 1.88 × 10-5M StN15 - group 4, or a blend of these - group 5. Following this, AEP formation occurred (2 h) and an enamel biopsy (10 µL, 0.01 m HCl, pH 2.0, 10 s) was conducted on one incisor. The biopsy acid was then analyzed for calcium (Arsenazo method). The vestibular surfaces of the other teeth were treated with the same acid. Acid-resistant proteins in the residual AEP were then collected and analyzed quantitatively via proteomics.

RESULTS

Compared to control, treatment with the proteins/peptide, mixed or isolated, markedly enhanced acid-resistant proteins in the AEP. Notable increases occurred in pyruvate kinase PKM (11-fold, CaneCPI-5), immunoglobulins and submaxillary gland androgen-regulated protein 3B (4-fold, StN15), Hb, and lysozyme C (2-fold, StN15). Additionally, a range of proteins not commonly identified in the AEP but known to bind calcium or other proteins were identified in groups treated with the tested proteins/peptide either in isolation or as a mixture. The mean (SD, mM) calcium concentrations released from enamel were 3.67 ± 1.48a, 3.11 ± 0.72a, 1.94 ± 0.57b, 2.37 ± 0.90a, and 2.38 ± 0.45a for groups 1-5, respectively (RM-ANOVA/Tukey, p < 0.05).

CONCLUSIONS

Our findings demonstrate that all treatments, whether using a combination of proteins/peptides or in isolation, enhanced acid-resistant proteins in the AEP. However, only HB showed effectiveness in protecting against intrinsic erosive demineralization. These results pave the way for innovative preventive methods against intrinsic erosion, using "acquired pellicle engineering" techniques.

Solutions containing a statherin-derived peptide reduce enamel erosion in vitro

The effect of solutions containing a statherin-derived peptide (Stn15pSpS) on the protection against enamel erosion in vitro was evaluated. Bovine enamel specimens were divided into 4 groups (n = 15/group): 1) Deionized water (negative control), 2) Elmex Erosion Protection™ (positive control), 3) 1.88 × 10-5 M Stn15pSpS and 4) 3.76 × 10-5 M Stn15pSpS. The solutions were applied on the specimens for 1 min. Stimulated saliva was collected from 3 donors and used to form a 2-h acquired pellicle on the specimens. Then, the specimens were submitted to an erosive pH-cycling protocol 4 times/day, for 7 days (0.01 M HCl pH 2.0/45 s, artificial saliva/2 h, and artificial saliva overnight). The solutions were applied again during pH cycling, 2 times/day for 1 min after the first and last erosive challenges. Enamel loss (µm) was assessed by contact profilometry. Data were analyzed by Kruskal-Wallis and Dunn's test (p < 0.05). The best protection against erosion was conferred by Elmex Erosion Protection that significantly differed from all the other treatments, followed by the solutions containing Stn15pSpS, regardless of the concentration. However, 3.76 × 10-5 M Stn15pSpS did not differ from the negative control. The solution containing the lower concentration of Stn15pSpS protected against erosion in vitro, which should be confirmed using protocols that more closely resemble the clinical condition.

Gels containing statherin-derived peptide protect against enamel and dentin erosive tooth wear in vitro

The effect of gels containing a statherin-derived peptide (Stn) on the protection against enamel and dentin erosive tooth wear (ETW) in vitro was evaluated. Bovine enamel and dentin specimens were divided into 2 groups (n = 15 and 18/group for enamel and dentin, respectively) that were treated with Chitosan or Carboxymethylcellulose (CMC) gels containing Stn15pSpS at 1.88 × 10-5 M or 3.76 × 10-5 M. Chitosan or CMC gels without active ingredients served as negative controls, while chitosan gel containing 1.23% F (as NaF) and acidulated phosphate fluoride gel (1.23% F) served as positive controls. The gels were applied on the specimens for 4 min. Stimulated saliva was collected from 3 donors and used to form a 2-h acquired pellicle on the specimens. Then, the specimens were submitted to an erosive pH cycling protocol 4 times/day for 7 days (0.01 M HCl pH 2.0/45 s, artificial saliva/2 h, and artificial saliva overnight). The gels were applied again during pH cycling, 2 times/day for 4 min after the first and last erosive challenges. Enamel and dentin loss (μm) were assessed by contact profilometry. Scanning electron microscopy (SEM) was analyzed using a cold field emission. Data were analyzed by two-way ANOVA (for chitosan and CMC gels, separately) and Tukey's multiple comparison test. SEM images showed changes to enamel topography after application oft the gels containing Stn or F. Regarding CMC-based gels, for enamel, none of the treatments significantly reduced ETW in comparison with placebo; for dentin, however, gels containing Stn, regardless the concentration, significantly reduced the ETW. Moreover, Chitosan-based gels, regardless the Stn concentration, were able to protect enamel and dentin against ETW. Gels containing Stn might be a new approach to protect against ETW.

Rinsing with Statherin-Derived Peptide Alters the Proteome of the Acquired Enamel Pellicle

Changes in the proteomic profile of the acquired enamel pellicle (AEP) formed for 3 min or 2 h after rinsing with a peptide containing the 15 N-terminal residues of statherin, with serines 2 and 3 phosphorylated (StatpSpS), were evaluated. Nine volunteers participated in 2 consecutive days. Each day, after professional tooth cleaning, they rinsed for 1 min with 10 mL of phosphate buffer containing 1.88 × 10-5 M StatpSpS or phosphate buffer only (control). The acquired pellicle formed on enamel after 3 min or 2 h was collected with electrode filter papers soaked in 3% citric acid. After protein extraction, samples were analyzed by quantitative shotgun label-free proteomics. In the 3-min AEP, 19 and 131 proteins were uniquely identified in the StatpSpS and control groups, respectively. Proteins typically found in the AEP were only found in the latter. Only 2 proteins (neutrophil defensins) were increased upon treatment with StatpSpS, while 65 proteins (among which are several typical AEP proteins) were decreased. In the 2-h AEP, 50 and 108 proteins were uniquely found in StatpSpS and control groups, respectively. Hemoglobin subunits and isoforms of keratin were only found in the StatpSpS group, while cystatin-C, cathepsin D, and cathepsin G, isoforms of heat shock 70 and protocadherin were exclusively found in the control group. In addition, 23 proteins were increased upon treatment with StatpSpS, among which are histatin-1, serum albumin, and isoforms of neutrophil defensin and keratin, while 77 were decreased, most of them were typical AEP proteins. In both evaluated periods, rinsing with StatpSpS profoundly changed the proteomic profile of the AEP, which might impact the protective role of this integument against carious or erosive demineralization. This study provides important insights on the dynamics of the protein composition of the AEP along time, after rinsing with a solution containing StatpSpS.

Acquired pellicle engineering with proteins/peptides: Mechanism of action on native human enamel surface

OBJECTIVE

This study investigated the mechanism of action of different proteins/peptides (separately or in combination), focusing on how they act directly on the native enamel surface and on modifying the salivary pellicle.

METHODS

A total of 170 native human enamel specimens were prepared and submitted to different treatments (2 h; 37 °C): with deionized water, CaneCPI-5, Hemoglobin, Statherin, or a combination of all three proteins/peptides. The groups were subdivided into treatment acting on the enamel surface (NoP - absence of salivary pellicle), and treatment modifying the salivary pellicle (P). Treatment was made (2 h; 37 °C) in all specimens, and later, for P, the specimens were incubated in human saliva (2 h; 37 °C). In both cases, the specimens were immersed in 1% citric acid (pH 3.6; 2 min; 25 °C). Calcium released from enamel (CaR) and its relative surface reflection intensity (%SRI) was measured after 5 cycles. Between-group differences were verified with two-way ANOVA, with "presence of pellicle" and "treatment" as factors (α = 0.05).

RESULTS

The presence of pellicle provided better protection regarding %SRI (p < 0.01), but not regarding CaR (p = 0.201). In relation to treatment, when compared to the control group, all proteins/peptides provided significantly better protection (p < 0.01 for %SRI and Car). The combination of all three proteins/peptides demonstrated the best protective effect (p < 0.01 for %SRI).

CONCLUSION

Depending on the protein or peptide, its erosion-inhibiting effect derives from their interaction with the enamel surface or from modifying the pellicle, so a combination of proteins and peptides provides the best protection.

CLINICAL SIGNIFICANCE

The present study opens a new direction for a possible treatment with a combination of proteins for native human enamel, which can act directly on the enamel surface as well on the modification of the salivary pellicle, for the prevention of dental erosion.

Rhamnolipid-Based Liposomes as Promising Nano-Carriers for Enhancing the Antibacterial Activity of Peptides Derived from Bacterial Toxin-Antitoxin Systems

Background

Antimicrobial resistance poses substantial risks to human health. Thus, there is an urgent need for novel antimicrobial agents, including alternative compounds, such as peptides derived from bacterial toxin-antitoxin (TA) systems. ParELC3 is a synthetic peptide derived from the ParE toxin reported to be a good inhibitor of bacterial topoisomerases and is therefore a potential antibacterial agent. However, ParELC3 is inactive against bacteria due to its inability to cross the bacterial membranes. To circumvent this limitation we prepared and used rhamnolipid-based liposomes to carry and facilitate the passage of ParELC3 through the bacterial membrane to reach its intracellular target - the topoisomerases.

Methods and Results

Small unilamellar liposome vesicles were prepared by sonication from three formulations that included 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine and cholesterol. ParELC3 was loaded with high efficiency into the liposomes. Characterization by DLS and TEM revealed the appropriate size, zeta potential, polydispersity index, and morphology. In vitro microbiological experiments showed that ParELC3 loaded-liposomes are more efficient (29 to 11 µmol·L⁻¹) compared to the free peptide (>100 µmol·L⁻¹) at inhibiting the growth of standard E. coli and S. aureus strains. RL liposomes showed high hemolytic activity but when prepared with POPC and Chol this activity had a significant reduction. Independently of the formulation, the vesicles had no detectable cytotoxicity to HepG2 cells, even at the highest concentrations tested (1.3 mmol·L⁻¹ and 50 µmol·L⁻¹ for rhamnolipid and ParELC3, respectively).

Conclusion

The present findings suggest the potential use of rhamnolipid-based liposomes as nanocarrier systems to enhance the bioactivity of peptides.

Pressure dependence of side chain 1H and 15N-chemical shifts in the model peptides Ac-Gly-Gly-Xxx-Ala-NH2

For interpreting the pressure induced shifts of resonance lines of folded as well as unfolded proteins the availability of data from well-defined model systems is indispensable. Here, we report the pressure dependence of 1H and 15N chemical shifts of the side chain atoms in the protected tetrapeptides Ac-Gly-Gly-Xxx-Ala-NH2 (Xxx is one of the 20 canonical amino acids) measured at 800 MHz proton frequency. As observed earlier for other nuclei the chemical shifts of the side chain nuclei have a nonlinear dependence on pressure in the range from 0.1 to 200 MPa. The pressure response is described by a second degree polynomial with the pressure coefficients B1 and B2 that are dependent on the atom type and type of amino acid studied. A number of resonances could be assigned stereospecifically including the 1H and 15N resonances of the guanidine group of arginine. In addition, stereoselectively isotope labeled SAIL amino acids were used to support the stereochemical assignments. The random-coil pressure coefficients are also dependent on the neighbor in the sequence as an analysis of the data shows. For Hα and HN correction factors for different amino acids were derived. In addition, a simple correction of compression effects in thermodynamic analysis of structural transitions in proteins was derived on the basis of random-coil pressure coefficients.

Adepamycin: design, synthesis and biological properties of a new peptide with antimicrobial properties

Antimicrobial peptides (AMP) are molecules with a broad spectrum of activities that have been identified in most living organisms. In addition, synthetic AMPs designed from natural polypeptides have been largely investigated. Here, we designed a novel AMP using the amino acid sequence of a plant trypsin inhibitor from Adenanthera pavonina seeds (ApTI) as a template. The 176 amino acid residues ApTI sequence was cleaved in silico using the Collection of Antimicrobial Peptides (CAMP_R3), through the sliding-window method. Further improvements in AMP structure were carried out, resulting in adepamycin, an AMP designed from ApTI. Adepamycin showed antimicrobial activity from 0.9 to 3.6 μM against Escherichia coli, Klebsiella oxytoca, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Staphylococcus aureus strains. Moreover, this peptide also displayed activity against Candida albicans and Candida tropicalis. No toxic effects were observed on healthy human cells. Studies on the mechanism of action of adepamycin were carried out using an E. coli and C. tropicalis. Adepamycin triggers membrane disturbances, leading to intracellular nucleic acids release in E. coli. For C. tropicalis, an initial interference with the plasma membrane integrity is followed by the formation of intracellular reactive oxygen species (ROS), leading to apoptosis. Structurally, adepamycin was submitted to circular dichroism spectroscopy, molecular modeling and molecular dynamics simulations, revealing an environment-dependent α-helical structure in the presence of 2,2,2- trifluoroethanol (TFE) and in contact with mimetic vesicles/membranes. Therefore, adepamycin represents a novel lytic AMP with dual antibacterial and antifungal properties.

Development of a novel anti-biofilm peptide derived from profilin of Spodoptera frugiperda

Candida yeast infections are the fourth leading cause of death worldwide. Peptides with antimicrobial activity are a promising alternative treatment for such infections. Here, the antifungal activity of a new antimicrobial peptide-PEP-IA18-was evaluated against Candida species. PEP-IA18 was designed from the primary sequence of profilin, a protein from Spodoptera frugiperda, and displayed potent activity against Candida albicans and Candida tropicalis, showing a minimum inhibitory concentration (MIC) of 2.5 µM. Furthermore, the mechanism of action of PEP-IA18 involved interaction with the cell membrane (ergosterol complexation). Treatment at MIC and/or 10 × MIC significantly reduced biofilm formation and viability. PEP-IA18 showed low toxicity toward human fibroblasts and only revealed hemolytic activity at high concentrations. Thus, PEP-IA18 exhibited antifungal and anti-biofilm properties with potential applicability in the treatment of infections caused by Candida species.

A Novel Antifungal System With Potential for Prolonged Delivery of Histatin 5 to Limit Growth of Candida albicans

Currently 75–88% of fungal infections are caused by Candida species, and Candida albicans is the main microorganism that causes these infections, especially oral candidiasis. An option for treatment involves the use of the antifungal peptide Histatin 5 (Hst 5), which is naturally found in human saliva but undergoes rapid degradation when present in the oral cavity, its site of action. For this reason, it is important to develop a way of applying this peptide to the oral lesions, which promotes the gradual release of the peptide. In the present study, we have evaluated the development of liposomes of different lipid compositions, loaded with the peptide as a way to promote its release slowly and gradually, preserving its antifungal potential. For this, the peptide 0WHistatin 5, an analog of the peptide Hst 5, was synthesized, which contains the amino acid tryptophan in its sequence. The solid phase synthesis method was used, followed by cleavage and purification. The liposomes were produced by thin film hydration technique in three different lipid compositions, F1, F2, and F3 and were submitted to an extrusion and sonication process to standardize the size and study the best technique for their production. The liposomes were characterized by dynamic light scattering, and tests were performed to determine the encapsulation efficiency, release kinetics, stability, and evaluation of antifungal activity. The extruded liposomes presented average size in the range of 100 nm, while sonicated liposomes presented a smaller size in the range of 80 nm. The encapsulation efficiency was higher for the sonicated liposomes, being 34.5% for F1. The sonicated F3 presented better stability when stored for 60 days at 4°C. The liposomes showed the ability to release the peptide for the total time of 96 h, with the first peak after 5 h, and a further increase of the released after 30 h. Time-kill assay showed that the liposomes were able to control yeast growth for 72 h. The data suggest that the liposomes loaded with 0WHistatin 5 maintained the action of the peptide and were able to limit the growth of C. albicans, being a suitable system for use in the treatment of oral candidiasis.

Self-association and folding in membrane determine the mode of action of peptides from the lytic segment of sticholysins

Sticholysin I and II (Sts: St I and St II) are proteins of biomedical interest that form pores upon the insertion of their N-terminus in the plasma membrane. Peptides spanning the N-terminal residues of StI (StI_1-31) or StII (StII_1-30) can mimic the permeabilizing ability of these toxins, emerging as candidates to rationalize their potential biomedical applications. These peptides have different activities that correlate with their hydrophobicity. However, it is not clear how this property contributes to peptide folding in solution or upon binding to membranes. Here we compared the conformational properties of these peptides and shorter versions lacking the hydrophobic segment 1-11 of StI (StI_12-31) or 1-10 of StII (StII_11-30). Folding of peptides was assessed in solution and in membrane mimetic systems and related with their ability to bind to membranes and to permeabilize lipid vesicles. Our results suggest that the differences in activity among peptides could be ascribed to their different folding propensity and different membrane binding properties. In solution, StII_1-30 tends to acquire α-helical conformation coexisting with self-associated structures, while StI_1-31 remains structureless. Both peptides fold as α-helix in membrane; but StII_1-30 also self-associates in the lipid environment, a process that is favored by its higher affinity for membrane. We stress the contribution of the non-polar/polar balance of the 1-10 amino acid sequence of the peptides as a determining factor for different self-association capabilities. Such difference in hydrophobicity seems to determine the molecular path of peptides folding upon binding to membranes, with an impact in their permeabilizing activity. This study contributes to a better understanding of the molecular mechanisms underlying the permeabilizing activity of Sts N-terminal derived peptides, with connotation for the exploitation of these small molecules as alternative of the full-length toxins in clinical settings.

Insights on the structure-activity relationship of peptides derived from Sticholysin II

Sticholysin II (StII) is a pore-forming actinoporin from the sea anemone Stichodactyla helianthus. A mechanistic model of its action has been proposed: proteins bind to cell membrane, insert their N-termini into the lipid core and assemble into homo-tetramer pores responsible for host-cell death. Because very likely the first 10 residues of StII N-terminus are critical for membrane penetration, to dissect the molecular details of that functionality, we studied two synthetic peptides: StII1-30 and StII16-35 . They show diverse haemolytic and candidacidal activity that correlate with distinct orientations in SDS micelles. NMR shows that StII1-30 partly inserts into the micelle, while StII16-35 lays on the micelle surface. These results justify the diverse concentration dependence of their candidacidal activity supposing a different mechanism of action and providing new hints on StII lytic activity at molecular level. Biotechnological application of these peptides, focused on the development of therapeutic immunocomplexes, may be envisaged.

HsDHODH Microdomain-Membrane Interactions Influenced by the Lipid Composition

Human dihydroorotate dehydrogenase (HsDHODH) enzyme has been studied as selective target for inhibitors to block the enzyme activity, intending to prevent proliferative diseases. The N-terminal microdomain seems to play an important role in the enzyme function. However, the molecular mechanism of action and dynamics of this region are not totally understood yet. This study analyzes the interaction and conformation in model membranes of HsDHODH microdomain using peptide analogues containing the paramagnetic amino acid TOAC at strategic positions. In buffer solution, the analogues presented a disordered conformation, but acquired a high content of α-helical structure in membrane mimetics, which was found to be lipid dependent. The microdomain peptide structure in micelles showed a very different peptide conformation when compared to the reported crystal structure, displaying a conformational flexibility of its helices, promoted by the connecting loop, which might be functionally relevant. Electron spin resonance in membrane compositions containing POPC, POPE, and cardiolipin showed that interaction of the analogues was enhanced by the presence of cardiolipin, indicating that the microdomain preferentially interacts with cardiolipin-containing membranes. Therefore, the great flexibility of the microdomain and the cardiolipin affinity should be considered in further studies aimed at finding new inhibitory compounds to fight proliferative diseases.

Pressure dependence of side chain 13C chemical shifts in model peptides Ac-Gly-Gly-Xxx-Ala-NH2

For evaluating the pressure responses of folded as well as intrinsically unfolded proteins detectable by NMR spectroscopy the availability of data from well-defined model systems is indispensable. In this work we report the pressure dependence of ¹³C chemical shifts of the side chain atoms in the protected tetrapeptides Ac-Gly-Gly-Xxx-Ala-NH₂ (Xxx, one of the 20 canonical amino acids). Contrary to expectation the chemical shifts of a number of nuclei have a nonlinear dependence on pressure in the range from 0.1 to 200 MPa. The size of the polynomial pressure coefficients B ₁ and B ₂ is dependent on the type of atom and amino acid studied. For H^N, N and C^α the first order pressure coefficient B ₁ is also correlated to the chemical shift at atmospheric pressure. The first and second order pressure coefficients of a given type of carbon atom show significant linear correlations suggesting that the NMR observable pressure effects in the different amino acids have at least partly the same physical cause. In line with this observation the magnitude of the second order coefficients of nuclei being direct neighbors in the chemical structure also are weakly correlated. The downfield shifts of the methyl resonances suggest that gauche conformers of the side chains are not preferred with pressure. The valine and leucine methyl groups in the model peptides were assigned using stereospecifically ¹³C enriched amino acids with the pro-R carbons downfield shifted relative to the pro-S carbons.

NMR structures and molecular dynamics simulation of hylin-a1 peptide analogs interacting with micelles

Antimicrobial peptides are recognized candidates with pharmaceutical potential against epidemic emerging multi-drug resistant bacteria. In this study, we use nuclear magnetic resonance spectroscopy and molecular dynamics simulations to determine the unknown structure and evaluate the interaction with dodecylphosphatidylcholine (DPC) and sodium dodecylsulphate (SDS) micelles with three W⁶ -Hylin-a1 analogs antimicrobial peptides (HyAc, HyK, and HyD). The HyAc, HyK, and HyD bound to DPC micelles are all formed by a unique α-helix structure. Moreover, all peptides reach the DPC micelles' core, which thus suggests that the N-terminal modifications do not influence the interaction with zwiterionic surfaces. On the other hand, only HyAc and HyK peptides are able to penetrate the SDS micelle core while HyD remains always at its surface. The stability of the α-helical structure, after peptide-membrane interaction, can also be important to the second step of peptide insertion into the membrane hydrophobic core during permeabilization. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

SARS-CoV fusion peptides induce membrane surface ordering and curvature

Viral membrane fusion is an orchestrated process triggered by membrane-anchored viral fusion glycoproteins. The S2 subunit of the spike glycoprotein from severe acute respiratory syndrome (SARS) coronavirus (CoV) contains internal domains called fusion peptides (FP) that play essential roles in virus entry. Although membrane fusion has been broadly studied, there are still major gaps in the molecular details of lipid rearrangements in the bilayer during fusion peptide-membrane interactions. Here we employed differential scanning calorimetry (DSC) and electron spin resonance (ESR) to gather information on the membrane fusion mechanism promoted by two putative SARS FPs. DSC data showed the peptides strongly perturb the structural integrity of anionic vesicles and support the hypothesis that the peptides generate opposing curvature stresses on phosphatidylethanolamine membranes. ESR showed that both FPs increase lipid packing and head group ordering as well as reduce the intramembrane water content for anionic membranes. Therefore, bending moment in the bilayer could be generated, promoting negative curvature. The significance of the ordering effect, membrane dehydration, changes in the curvature properties and the possible role of negatively charged phospholipids in helping to overcome the high kinetic barrier involved in the different stages of the SARS-CoV-mediated membrane fusion are discussed.

Pressure dependence of backbone chemical shifts in the model peptides Ac-Gly-Gly-Xxx-Ala-NH2

For a better understanding of nuclear magnetic resonance (NMR) detected pressure responses of folded as well as unstructured proteins the availability of data from well-defined model systems are indispensable. In this work we report the pressure dependence of chemical shifts of the backbone atoms (1)H(α), (13)C(α) and (13)C' in the protected tetrapeptides Ac-Gly-Gly-Xxx-Ala-NH2 (Xxx one of the 20 canonical amino acids). Contrary to expectation the chemical shifts of these nuclei have a nonlinear dependence on pressure in the range from 0.1 to 200 MPa. The polynomial pressure coefficients B 1 and B 2 are dependent on the type of amino acid studied. The coefficients of a given nucleus show significant linear correlations suggesting that the NMR observable pressure effects in the different amino acids have at least partly the same physical cause. In line with this observation the magnitude of the second order coefficients of nuclei being direct neighbors in the chemical structure are also weakly correlated.

Jatrophidin I, a cyclic peptide from Brazilian Jatropha curcas L.: isolation, characterization, conformational studies and biological activity

A cyclic peptide, jatrophidin I, was isolated from the latex of Jatropha curcas L. Its structure was elucidated by extensive 2D NMR spectroscopic analysis, with additional conformational studies performed using Molecular Dynamics/Simulated Annealing (MD/SA). Jatrophidin I had moderate protease inhibition activity when compared with pepstatin A; however, the peptide was inactive in antimalarial, cytotoxic and antioxidant assays.

Pressure response of amide one-bond J-couplings in model peptides and proteins

The pressure dependence of the one-bond indirect spin-spin coupling constants (1)J(N-H) was studied in the protected tetrapeptides Ac-Gly-Gly-Xxx-Ala-NH2 (with Xxx being one of the 20 proteinogenic amino acids). The response of the (1)J(N-H) coupling constants is amino acid type specific, with an average increase of its magnitude by 0.6 Hz at 200 MPa. The variance of the pressure response is rather large, the largest pressure effect is observed for asparagine where the coupling constant becomes more negative by -2.9 Hz at 200 MPa. The size of the J-coupling constant at high pressure is positively correlated with its low pressure value and the β-propensity, and negatively correlated with the amide proton shift and the first order nitrogen pressure coefficient and the electrostatic solvation free energy.

Pressure Dependence of 15N Chemical Shifts in Model Peptides Ac-Gly-Gly-X-Ala-NH2

High pressure NMR spectroscopy has developed into an important tool for studying conformational equilibria of proteins in solution. We have studied the amide proton and nitrogen chemical shifts of the 20 canonical amino acids X in the random-coil model peptide Ac-Gly-Gly-X-Ala-NH₂, in a pressure range from 0.1 to 200 MPa, at a proton resonance frequency of 800 MHz. The obtained data allowed the determination of first and second order pressure coefficients with high accuracy at 283 K and pH 6.7. The mean first and second order pressure coefficients <B₁^15N> and <B₂^15N> for nitrogen are 2.91 ppm/GPa and −2.32 ppm/GPa², respectively. The corresponding values <B₁^1H> and <B₂^1H> for the amide protons are 0.52 ppm/GPa and −0.41 ppm/GPa². Residual dependent ¹J_1H15N-coupling constants are shown.

Hylin a1, the first cytolytic peptide isolated from the arboreal South American frog Hypsiboas albopunctatus ("spotted treefrog")

RP-HPLC fractionation of the electrically stimulated skin secretion of the arboreal South American frog Hypsiboas albopunctatus ("spotted treefrog") led to the isolation of a cytolytic C-terminally amidated peptide. This novel peptide, named hylin a1 (Hy-a1), consists of 18 amino acid residues (IFGAILPLALGALKNLIK-NH(2)). The alpha-helical structure of the synthetic hylin a1 peptide was confirmed by CD spectroscopy in the presence of 60% (v/v) TFE. The synthetic peptide displayed broad-spectrum antimicrobial activity against Gram-negative and Gram-positive bacteria including Escherichia coli, Staphylococcus aureus, Enterococcus faecalis, Bacillus subtilis and Pseudomonas aeruginosa and also against fungi (Candida albicans, C. krusei, C. parapsilosis and Cryptococcus neoformans). Hylin a1 was also able to disrupt human erytrocytes (HC(50)=18 microM). Similarity analysis using PSI-BLAST revealed 50-44% of identity to maximins Hv, H16, H15 and H10 from Bombina maxima and also to hylins b1 and b2 (Hy-b1 and Hy-b2) from Hypsiboas lundii (synonym: Hyla biobeba).

Correlations between differences in amino-terminal sequences and different hemolytic activity of sticholysins

Sticholysins I and II (St I and St II) are cytolysins produced by the sea anemone Stichodactyla helianthus. In spite of their 93% sequence homology, St II is more hemolytic against human erythrocytes than St I. In order to establish the possible causes of this difference, we studied the hemolytic activity of synthetic peptides containing sequences from the N-termini of both proteins. The results demonstrated that the differences in hemolytic activity of the toxins could be ascribed at least partly to differences in their N-termini.

Comparative investigation of the cleavage step in the synthesis of model peptide resins: implications for Nalpha-9-fluorenylmethyloxycarbonyl-solid phase peptide synthesis

Based on our studies of the stability of model peptide-resin linkage in acid media, we previously proposed a rule for resin selection and a final cleavage protocol applicable to the Nalpha-tert-butyloxycarbonyl (Boc)-peptide synthesis strategy. We found that incorrect choices resulted in decreases in the final synthesis yield, which is highly dependent on the peptide sequence, of as high as 30%. The present paper continues along this line of research but examines the Nalpha-9-fluorenylmethyloxycarbonyl (Fmoc)-synthesis strategy. The vasoactive peptide angiotensin II (AII, DRVYIHPF) and its [Gly8]-AII analogue were selected as model peptide resins. Variations in parameters such as the type of spacer group (linker) between the peptide backbone and the resin, as well as in the final acid cleavage protocol, were evaluated. The same methodology employed for the Boc strategy was used in order to establish rules for selection of the most appropriate linker-resin conjugate or of the peptide cleavage method, depending on the sequence to be assembled. The results obtained after treatment with four cleavage solutions and with four types of linker groups indicate that, irrespective of the circumstance, it is not possible to achieve complete removal of the peptide chains from the resin. Moreover, the Phe-attaching peptide at the C-terminal yielded far less cleavage (50-60%) than that observed with the Gly-bearing sequences at the same position (70-90%). Lastly, the fastest cleavage occurred with reagent K acid treatment and when the peptide was attached to the Wang resin.

Study of the effect of the peptide loading and solvent system in SPPS by HRMAS-NMR

The SPPS methodology has continuously been investigated as a valuable model to monitor the solvation properties of polymeric materials. In this connection, the present work applied HRMAS-NMR spectroscopy to examine the dynamics of an aggregating peptide sequence attached to a resin core with varying peptide loading (up to 80%) and solvent system. Low and high substituted BHAR were used for assembling the VQAAIDYING sequence and some of its minor fragments. The HRMAS-NMR results were in agreement with the swelling of each resin, i.e. there was an improved resolution of resonance peaks in the better solvated conditions. Moreover, the peptide loading and the attached peptide sequence also affected the spectra. Strong peptide chain aggregation was observed mainly in highly peptide loaded resins when solvated in CDCl3. Conversely, due to the better swelling of these highly loaded resins in DMSO, improved NMR spectra were acquired in this polar aprotic solvent, thus enabling the detection of relevant sequence-dependent conformational alterations. The more prominent aggregation was displayed by the VQAAIDYING segment and not by any of its intermediary fragments and these findings were also corroborated by EPR studies of these peptide-resins labelled properly with an amino acid-type spin probe.