Influence of Dy3+ ion concentration on photoluminescence and energy transfer mechanism of promising KBaScSi3O9 phosphors for warm white LEDs

A novel white light emitting silicate-based phosphor of Dy³⁺ activated KBaScSi₃O₉ (xDyKBS) was prepared by a conventional solid state method. Powder X-ray diffraction patterns represent the pure phase of synthesized materials that was formed with monoclinic structure. The metal-ligand bonding nature and electronic band structure have been examined optical absorption spectra. The luminescence emission curves of the silicate phosphors display an intense yellow emission peak at 579 nm and a blue emission peak at 491 nm. Among the emission bands, the band observed in the yellow region due to ⁴F_9/2→⁶H_13/2 transition was found to be higher intensity. The radiative parameters like transition probabilities (A_R), branching ratios (β_R) and stimulated emission cross-section (σ_P^E) values were calculated using Judd-Ofelt parameters and refractive index values for the observed transitions in emission spectra. The life time measurements were made for ⁴F_9/2 → ⁶H_13/2 transition of all the studied samples by keeping an excitation at 350 nm and emission at 579 nm and decay curves were fitted to bi-exponential fitting method. The CCT values obtained from the color coordinates suggested that present xDyKBS phosphors can emit warm and neutral white light depending upon the dopant concentration under near-UV excitation. Our results demonstrated that the optimum concentration 0.05DyKBS phosphor can be successfully utilized as a promising and potential candidate for various innovative photonic applications like warm white LEDs, solar cells, optical sensors and lasers.

Mass spectral analysis of acetylated peptides: Implications in proteomics

Sequence determination of peptides using mass spectrometry plays a crucial role in the bottom-up approaches for the identification of proteins. It is crucially important to minimise false detection and validate sequence of the peptides in order to correctly identify a protein. Chemical modification of peptides followed by mass spectrometry is an option for improving the spectral quality. In silico-derived tryptic peptides with different N-terminal amino acids were designed from human proteins and synthesized. The effect of acetylation on the fragmentation of peptides was studied. N-terminal acetylation of the tryptic peptides was shown to form b₁-ions, improve the abundance and occurrence of b-ions. In some cases, the intensity and occurrence of some y-ions also varied. Thus, it is demonstrated that acetylation plays an important role in improving the de novo sequencing efficiency of the peptides. The acetylation method was extended to tryptic peptides generated from the proteome of an Antarctic bacterium Pseudomonas syringae Lz4W using the proteomics work flow and mass spectra of the peptides were analysed. Comparison of the MS/MS spectra of the acetylated and unacetylated peptides revealed that acetylation helped in improving the spectral quality and validated the peptide sequences. Using this method, 673 proteins of the 1070 proteins identified were validated.

Silver (Ag) nanoparticles enhanced luminescence properties of Dy3+ ions in borotellurite glasses for white light applications

In the present work, the structural and optical properties of borotellurite glasses co-doped with Dy³⁺ ions and Ag nanoparticles were investigated. From HR-TEM analysis, the average Ag nanoparticle diameter was calculated as 13.7 ± 1 nm. The negative sign of the bonding parameter explored the ionic nature of metal-ligand (DyO) bonds. The emission spectra exhibited three emission bands in blue, yellow and red regions corresponding to ⁴F_9/2 → ⁶H_15/2, ⁴F_9/2 → ⁶H_13/2 and ⁴F_9/2 → ⁶H_11/2 transitions, respectively. The Yellow/Blue (Y/B) ratio of optimal BTD0.5A glass was found to be 1.881 and this low Y/B ratio indicated the fact that Dy³⁺ ions were located in higher symmetrical ligand environment. The CCT values are found to vary from 3717 to 3800 K and hence the present glasses may emit cool white light when excited with UV lamp. The radiative parameters were calculated for all the emission transitions by using JO theory. The decay curves are found to show non-exponential behavior for all the studied glasses. The obtained results were discussed in detail and compared with similar reported glasses.

Characterization of acetylated histidine b1-ion structure: A competition between oxazolone and side chain imidazole moiety

The detection of post-translational modifications of proteins is an important comprehensive research area. Over the years, proteomic studies involving protein acetylation have attracted a great deal of attention. In the present study, we have focussed on the acetylation of histidine and the intrinsic stability of b₁-ion of oxazolone ring and/or with side chain imidazole bicyclic product. The formation of oxazolone structure may occur when an amino moiety undergoes acetylation reaction and when it is present in the vicinity of the side chain imidazole moiety. Tryptic peptides generated from the proteins of Acenitobacter radioresistens MMC5-containing N-terminal histidine were explored in a standard proteomic workflow. Formation of [Formula: see text] ion with an oxazolone ring in these peptides has been supported by a tandem mass spectrometric study of a synthetic peptide and density functional theory calculations. The results obtained from this study have implications in understanding the fragmentation of the peptides generated in the proteomic workflows.

Detection of peptides with intact phosphate groups using MALDI TOF/TOF and comparison with the ESI-MS/MS

A wide variety of post-translational modifications such as oxidation, phosphorylation, glycosylation, methylation, and acetylation play critical roles in cellular functions. Detection of post-translational modifications in proteins is important to understand their crucial roles in cellular functions. Identifying each modification requires special attention in mass spectral acquisition and analysis. Here, we report a mass spectral method for the detection of multiple phosphorylations in peptides by analyzing their products after fragmentation. Synthetic peptides were used to identify these modifications by matrix-assisted laser desorption/ionization (MALDI) TOF/TOF. Peptides with serine, threonine, and tyrosine were used with mono- to tetra-phosphorylation sites in different combinations to get insights into their fragmentation and identify the location of these sites. The y-ion series were observed without the loss of phosphate groups and were thus very useful in determining the localization and sequence of the phosphate residues. Acetylation of the peptides was found to be useful in detecting the b1-ion and helped in identifying the N-terminus. When a mixture of the phosphorylated peptides (from mouse protein sequences) were analyzed by LC-MS/MS on a Velos Orbitrap Mass Spectrometer and the data subjected to analysis by Sequest using the mouse database, the peptides were identified along with the parent proteins. A comparison of MALDI TOF/TOF spectra with ESI MS/MS helped in eliminating falsely discovered peptides using the database search.

Spectroscopic properties of Sm3+ ions doped Alkaliborate glasses for photonics applications

A new series of Sm³⁺ doped alkaliborate glasses have been prepared by melt quenching technique and their structural and spectroscopic properties were analysed employing XRD, FTIR, optical absorption, photoluminescence and decay spectral measurements in order to explore their suitability for photonic applications. The amorphous nature have been confirmed through XRD analysis and the FTIR spectra reveal the presence of fundamental stretching and bending vibrations of the borate networks in the prepared glasses. From the absorption peak positions, bonding parameter (δ) values were calculated to examine the nature of the metal-ligand bond. The optical band gap (E_opt) corresponds to the direct and indirect allowed transitions and the Urbach energies (ΔE) were calculated from the absorption spectra to understand the electronic band structure of the studied glasses. The Judd-Ofelt (JO) intensity parameters Ω_λ (λ=2, 4 and 6) were determined to explore the symmetry of the ligand environment around the Sm³⁺ ions in the studied glasses. The luminescence spectra exhibit four emission bands in the visible region due to the ⁴G_5/2→⁶H_5/2, ⁶H_7/2, ⁶H_9/2 and ⁶H_11/2 transitions. The radiative parameters such as transition probability (A), stimulated emission cross-section (σ_P^E), branching ratios (β_R) and radiative lifetime (τ_R) have been determined from the luminescence spectra using JO theory to ensure the suitability of the studied glasses for optoelectronic applications. The luminescence spectra were characterized through CIE 1931 chromaticity diagram to examine the dominant emission color of the studied glasses. The lifetime values of the Sm³⁺ doped studied glasses pertaining to the ⁴G_5/2 excited level have been determined through decay curve measurements and the non-exponential decay curves were fitted to the Inokuti-Hirayama model to analyze the energy transfer mechanism between the nearby Sm³⁺ ions. The obtained results were discussed and compared with the similar reported glasses.

Protective role of E. coli outer membrane vesicles against antibiotics

The outer membrane vesicles (OMVs) from bacteria are known to posses both defensive and protective functions and thus participate in community related functions. In the present study, outer membrane vesicles have been shown to protect the producer bacterium and two other bacterial species from the growth inhibitory effects of some antibiotics. The OMVs isolated from E. coli MG1655 protected the bacteria against membrane-active antibiotics colistin, melittin. The OMVs of E. coli MG1655 could also protect P. aeruginosa NCTC6751 and A. radiodioresistens MMC5 against these membrane-active antibiotics. However, OMVs could not protect any of these bacteria against the other antibiotics ciprofloxacin, streptomycin and trimethoprim. Hence, OMVs appears to protect the bacterial community against membrane-active antibiotics and not other antibiotics, which have different mechanism of actions. The OMVs of E. coli MG1655 sequester the antibiotic colistin, whereas their protein components degrade the antimicrobial peptide melittin. Proteomic analysis of OMVs revealed the presence of proteases and peptidases which appear to be involved in this process. Thus, the protection of bacteria by OMVs against antibiotics is situation dependent and the mechanism differs for different situations. These studies suggest that OMVs of bacteria form a common defense for the bacterial community against specific antibiotics.

Comparison of oral fiberoptic intubation via a modified guedel airway or a laryngeal mask airway in infants and children

BACKGROUND

Though fiberoptic intubation (FOI) is considered the gold standard for securing a difficult airway in a child, it may be technically difficult in an anesthetized child. The hypothesis for this study was that it would be easier to perform FOI via a laryngeal mask airway (LMA) than a modified oropharyngeal airway with the advantage of maintaining anesthesia and oxygenation during the process.

MATERIALS AND METHODS

30 children aged 6 months to 5 years undergoing elective surgery under general anesthesia were randomized to two groups to have fiberoptic bronchoscope (FOB) guided intubation either via a modified Guedel airway (FOB-ORAL) or a classic LMA (FOB-LMA). In the FOB-LMA group, the LMA was removed when a second smaller endotracheal tube was anchored to the proximal end of the tracheal tube in place.

RESULTS

Oral fiberoptic intubation was successful in all children. The first attempt success rate was 11/15 (73.33%) in the FOB-LMA group and 3/15 (20%) in the FOB-ORAL group (P = 0.012). Subsequent attempts at intubation were successful after 90° anticlockwise rotation of the endotracheal tube over the FOB. The time taken for fiberoptic bronchoscopy was significantly less in FOB-LMA group (59.20 ± 42.85 sec vs 108.66 ± 52.43 sec). The incidence of desaturation was higher in the FOB-ORAL group (6/15 vs 0/15).

CONCLUSION

In children, fiberoptic bronchoscopy and intubation via an LMA has the advantage of being easier, with shorter intubation time and continuous oxygenation and ventilation throughout the procedure. Removal of the LMA following intubation requires particular care.

Characterization of chemical modification of tryptophan by matrix-assisted laser desorption/ionization mass spectrometry

Tert- butylation of tryptophan (2', 5', 7'- tri tertiary butyl tryptophan), formed during acidolytic cleavage of synthetic peptides Ac-KLVYWAE-CONH(2) (A-YW) and Ac-KLVWWAE-CONH(2) (A-WW), that are analogs of the fragment of Alzheimer's beta-amyloid peptide Ac-KLVFFAE-CONH(2), during solid-phase peptide synthesis, was characterized by matrix-assisted laser desorption/ionization time of flight/time of flight (MALDI TOF/TOF) mass spectrometry. Crude peptide was fractionated by high performance liquid chromatography. Peptide fractions were sequenced and modified tryptophan was determined with the help of MALDI TOF/TOF mass spectra. Thus, it is possible to pinpoint the particular tryptophan residue that undergoes modification during synthesis of peptides containing multiple tryptophan residues.

Detection of peptides covalently modified with multiple fatty acids by MALDI-TOF mass spectrometry

Analysis and characterization of membrane proteins and hydrophobic peptides by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) is a considerable challenge because of their lower ionization efficiency. Detergents are used to solubilize hydrophobic peptides and proteins. However, in MALDI-MS, the presence of detergents can cause considerable loss of signal intensity. The extent of interference depends on the matrix/sample preparation method and experimental conditions. In the present study, we have analyzed the MALDI response of multiple fatty acylated peptides in the presence of the matrices alpha-cyano-4-hydroxy cinnamic acid (HCCA) and 2,5-dihydroxy benzoic acid (DHB). The effect of adding the nonionic detergent n-octylglucoside (OG) was also examined. The presence of OG facilitated detection of tetrapalmitoylated peptide, particularly when HCCA was used as the matrix. When DHB was used as the matrix, good signal intensity was observed in the absence of OG. Lower laser pulse rate in the linear mode of analysis resulted in good signal intensity for the tetrapalmitoylated peptide. Conditions for obtaining good signal intensities for dipalmitoylated and N-myristoyl peptides with both HCCA and DHB as matrices were also investigated.

Bacterial lipid modification of proteins for novel protein engineering applications

Functioning of proteins efficiently at the solid-liquid interface is critical to not only biological but also modern man-made systems such as ELISA, liposomes and biosensors. Anchoring hydrophilic proteins poses a major challenge in this regard. Lipid modification, N-acyl-S-diacylglyceryl-Cys, providing an N-terminal hydrophobic membrane anchor is a viable solution that bacteria have successfully evolved but remains unexploited. Based on the current understanding of this ubiquitous and unique bacterial lipid modification it is possible to use Escherichia coli, the popular recombinant protein expression host, for converting a non-lipoprotein to a lipoprotein with a hydrophobic anchor at the N-terminal end. We report two strategies applicable to non-lipoproteins (with or without signal sequences) employing minimal sequence change. Taking periplasmic Shigella apyrase as an example, its signal sequence was engineered to include a lipobox, an essential determinant for lipid modification, or its mature sequence was fused to the signal sequence of abundant outer membrane lipoprotein, Lpp. Lipid modification was proved by membrane localization, electrophoretic mobility shift and mass spectrometric analysis. Substrate specificity and specific activity measurements indicated functional integrity after modification. In conclusion, a convenient protein engineering strategy for converting non-lipoprotein to lipoprotein for commercial application has been devised and tested successfully.

Cyclic homooligomers of furanoid sugar amino acids

Cyclic homooligomers of mannose-derived furanoid sugar amino acid 1 [H-Maa(Bn(2))-OH] were synthesized by using BOP reagent in the presence of DIPEA under dilute conditions that converted the sugar amino acid monomer directly into its cyclic homooligomers 3a and 4a. The glucose-based sugar amino acid 2 [H-Gaa(Bn(2))-OH] under the same reaction conditions gave a bicyclic lactam 5a as the major product. Cyclic homooligomers of 2 were prepared by cyclizing their linear precursors 6 and 7 leading to the formation of cyclic peptides 8a and 9a, respectively. Conformational analysis by NMR and constrained MD studies revealed that all the cyclic products, 3, 4, 8, and 9, had symmetrical structures. The deprotected cyclic trimer of Maa 3b displayed a conformation in which all the C=O and the N-H bonds of the molecule point in opposite directions. In the deprotected cyclic tetramer of Maa 4b, the COs and NHs were in the plane of the ring with the former pointing to outside and the latter inside the ring. The structure of the cyclic Gaa dimer 8b displayed an unusual six-membered intramolecular hydrogen bond between NH(i)() --> C3-O(i)()(-)(1) and a syn orientation between the C2-H and CO. In this molecule, the C2-hydrogens and the COs can be seen on one side of the ring while the NHs point to the other side. Addition of the bicyclic lactam 5b resulted in the influx of Na(+) ions across the lipid bilayer leading to the dissipation of valinomycin-mediated K(+) diffusion potential.

Effects of deleting a tripeptide sequence observed in muscular dystrophy patients on the conformation of synthetic peptides corresponding to the scaffolding domain of caveolin-3

The caveolin-scaffolding domain (CSD) is a region in caveolin-1 and 3 that mediates interactions with signaling proteins. In some patients with limb-girdle muscular dystrophy, a three amino acid micro deletion in the CSD has been observed. The conformations and aggregation behavior of synthetic peptides, corresponding to the CSD of caveolin-3: DGVWKVSYTTFTVSKYWFY and the sequence where TFT (underlined in the native sequence) has been deleted, have been investigated. Circular dichroism spectra and molecular dynamics simulations indicate distinctive differences in the conformations of the native and mutant sequences. The extent of self-association in aqueous medium is also less pronounced in the case of the peptide with the micro deletion. It is likely that the structural changes arising as a result of TFT deletion distrupt oligomerization and consequently mistargeting and degradation.

Host-defense antimicrobial peptides: importance of structure for activity

Antimicrobial peptides are important components of innate immunity in species across the evolutionary scale. Unlike therapeutically used antibiotics, this class of peptides exert their activity by permeabilizing bacterial membranes. Despite the seemingly common mechanism of action, there is considerable variation in their primary structures, length and number of positive charges. Host-defense antimicrobial peptides have been the subject of extensive biophysical studies with a view at delineate structural requirements for activity. In this article, the structures of host defence antibacterial peptides and the structural requirements for activity are reviewed.

The therapeutic potential of host-defense antimicrobial peptides

Species across the evolutionary scale from insects to mammals deploy peptides to counter microbial invaders. Although, there are considerable differences in the primary and secondary structures of these peptides, they exert their antimicrobial activity by common mechanisms ie. by membrane permeabilization. Extensive structure-function studies have been carried out on this class of antimicrobial peptides and 'designer' peptides have been generated which possess specific antimicrobial activity. In this article the physico-chemical properties and biological activities of host-defense peptides and 'designer' peptides would be reviewed with a view to explore whether they could be used as effective therapeutic agents.

NMR study of cyclic peptides with renin inhibitor activity

Several cyclic analogues of renin inhibitors, based on Glu-D-Phe-Lys motif have been investigated by NMR spectroscopy and molecular dynamics calculations (MD). The 15 membered macrocycle, resulting from Glu and Lys side-chain cyclization, exhibits conformational preference. The structural evidence from NMR shows the presence of hydrogen bond between Lys NH and Glu side-chain carbonyl, resulting in a 10 membered pseudo beta-turn-like structure. The structure of the cyclic moiety is similar in all the peptides, which takes at least two conformations around Calpha-Cbeta in Glu side chain. The restrained MD calculations further support such observations and show that the macrocycle is fairly rigid, with two conformations about the Glu Calpha-Cbeta bond. The linear peptide appendages, which are essential for activity in cyclic peptides, show an extended structure in the beta-region of Ramchandran plot. These calculations also demonstrate that for the most active peptide, two major conformers each exist about the Calpha-CO bond of the Lys, D-Trp and Leu residues. In this peptide, the cyclic moiety presents a negatively charged surface formed due to the carbonyl oxygens, which are thus available to form hydrogen bonds with the receptor. The linear fragment presents further binding sites with a surface which has the hydrophobic side chains of D-Trp, Leu and D-Met on one side and carbonyls on the other side.

Antibacterial activities and conformations of synthetic alpha-defensin HNP-1 and analogs with one, two and three disulfide bridges

Structure and biological activities of synthetic peptides corresponding to human alpha-defensin HNP-1, AC1YC2RIPAC3IAGERRYGTC4IYQGRLWAFC5C6 with the S-S connectivities: C1-C6, C2-C4, C3-C5, and its variants with one, two and three disulfide bridges were investigated. Oxidation of synthetic, reduced HNP-1 yielded a peptide with S-S connectivities C1-C3, C2-C4 and C5-C6, and not with the S-S linkages as in naturally occurring HNP-1. Selective protection of cysteine sulfhydryls was necessary for the formation of S-S bridges as in native HNP-1. Likewise, oxidation of peptide encompassing the segment from C2 to C5, resulted in the S-S linkages C2-C3 and C4-C5 instead of the expected linkage C2-C4 and C3-C5. Antibacterial activities were observed for all peptides, irrespective of how the S-S bridges were linked. Linear peptides without S-S bridges were inactive. Circular dichroism (CD) spectra suggest that peptides constrained by one and two S-S bridges do not form rigid beta-sheet structures in an aqueous environment. The spectrum of HNP-1 in an aqueous environment suggests the presence of a beta-hairpin conformation. In the presence of lipid vesicles, the S-S constrained peptides tend to adopt a beta-structure. Although the S-S connectivities observed in HNP-1 may be necessary for other physiological activities, such as chemotaxis, they are clearly not essential for antibacterial activity.

Antibacterial activities and conformations of bovine beta-defensin BNBD-12 and analogs:structural and disulfide bridge requirements for activity

Structure and biological activities of synthetic peptides corresponding to bovine neutrophil beta-defensin BNBD-12, GPLSC(1)GRNGGVC(2)IPIRC(3) PVPMRQIGTC(4) FGRPVKC(5) C(6)RSW with disulfide connectivities C(1)-C(5), C(2)-C(4) and C(3)-C(6) and its variants with one, two and three disulfide bridges have been investigated. Selective protection of cysteine thiols was necessary in the four and six cysteine containing peptides for the formation of disulfide connectivities as observed in BNBD-12. Circular dichroism (CD) spectra indicate that in aqueous medium, only a small fraction of molecules populate turn-like conformations. In the presence of micelles and lipid vesicles, the single, two and three disulfide containing peptides adopt beta-hairpin or beta-sheet structures. Antibacterial activity was observed for all the peptides, irrespective of the number of disulfide bridges or how they were connected. Our results suggest that a rigid beta-sheet structure or the presence of three disulfide bridges does not appear to be stringent requirements for antibacterial activity in beta-defensins.

Immunobiology of a synthetic luteinizing hormone receptor peptide 21-41

Immunization of adult male rabbits with a synthetic luteinizing hormone-receptor peptide (LH-RP; representing amino-acids 21-41 of the extracellular domain of the rat LH receptor) resulted in production of high-titer antibodies capable of interacting with particulate and cell-based LH receptors. The antibody produced was able to inhibit binding of 125I-labeled human chorionic gonadotropin (hCG) to a particulate sheep luteal LH receptor preparation by 40%-50%. Maximal inhibitory activity was correlated with high antibody titer. Immunocytometry revealed that the antibody could directly bind to cells having LH receptors, such as rat granulosa and Leydig cells. The antibodies recognized a 77-kilodalton membrane protein in Western blots of mouse testicular extracts. Interaction of endogenous Leydig cell LH receptor with the LH-RP antibody resulted in both hormone agonist and antagonistic activities. The hormone-mimicking activity (increase in serum testosterone over control) was confined only to the early phase of immunization when the antibody titer was low. Blockade of LH receptor during the later part of immunization resulted in a significant reduction in serum testosterone over controls and inhibition of spermatogenesis. DNA flow cytometry showed that a specific and significant inhibition of meiosis (transformation of primary spermatocytes to round and elongated spermatids P < .01) and spermiogenesis (transformation of round spermatids to elongated spermatids P < .0001) occurred following blockade of LH function.

Structure-function studies on the amphibian peptide brevinin 1E: translocating the cationic segment from the C-terminal end to a central position favors selective antibacterial activity

Brevinin 1E, which has the sequence FLPLLAGLAANFLPKIFCKITRKC, is an antimicrobial peptide isolated from the skin secretions of the European frog Rana esculenta. Both the linear and the disulfide-bridged forms have relatively broad-spectrum antibacterial as well as hemolytic activities. The antibacterial and hemolytic activities and biophysical properties of synthetic peptides corresponding to brevinin 1E and its analog in which the segment CKITRKC has been transposed to a central location resulting in the sequence FLPLLAGLCKITRKCAANFLPKIF have been investigated. Our studies indicate that the analog peptide has antibacterial activity comparable with brevinin 1E, but with considerably reduced hemolytic activity. The linear variant of the analog has no hemolytic activity, unlike the linear form of brevinin 1E. The biological activities can be explained on the basis of relative affinities for anionic and zwitterionic lipids. A cluster of cationic amino acids flanked on one side by a hydrophobic stretch of amino acids and another side composed of apolar amino acids appears to favor preferential antibacterial activity.

Effects of salt and denaturant on structure of the amino terminal alpha-helical segment of an antibacterial peptide dermaseptin and its binding to model membranes

The amino terminal 1-18 domain of dermaseptin s is an important determinant of its structure as well as the antibacterial activity. A thorough investigation on the structure of the 18-residue peptide (D18) and its binding to model membranes in presence of salt and denaturant guanidinium chloride has been carried out. In presence of salt, there is an increase in the fraction of peptide molecules in helical conformation. In presence of the denaturant, D18 is unordered, but addition of the structure-promoting solvent trifluoroethanol results in a transition to the helical conformation. In presence of denaturant, the peptide is unordered, but binding to lipid vesicles is not abolished. Investigation of model membrane permeabilizing ability of the peptide in solutions containing various proportions of sodium chloride and guanidinium chloride indicates that vesicle permeabilization parallels extent of binding. The peptide thus binds to lipid vesicles in an unfolded state. Since the peptide has propensity to fold into a helical conformation, lipid induced transition to a helical structure occurs, followed by membrane permeabilization as a result of pore formation.

Tigerinins: novel antimicrobial peptides from the Indian frog Rana tigerina

Four broad-spectrum, 11 and 12 residue, novel antimicrobial peptides have been isolated from the adrenaline-stimulated skin secretions of the Indian frog Rana tigerina. Sequences of these peptides have been determined by automated Edman degradation, by mass spectral analysis and confirmed by chemical synthesis. These peptides, which we have named as tigerinins, are characterized by an intramolecular disulfide bridge between two cysteine residues forming a nonapeptide ring. This feature is not found in other amphibian peptides. Conformational analysis indicate that the peptides tend to form beta-turn structures. The peptides are cationic and exert their activity by permeabilizing bacterial membranes. Tigerinins represent the smallest, nonhelical, cationic antimicrobial peptides from amphibians.

Biological activities of retro and diastereo analogs of a 13-residue peptide with antimicrobial and hemolytic activities

The biological activities of synthetic retro and diastereo analogs of PKLLKTFLSKWIG (SPFK), a 13-residue peptide with antimicrobial and hemolytic activities, have been investigated. Retro peptides with C-terminal acid and amide exhibited antibacterial activities comparable with those of SPFK. Their hemolytic activities were, however, only marginally lower. The diastereo analog with C-terminal acid was not antibacterial and was weakly hemolytic. Amidation of this analog could restore antibacterial activity. Both retro analogs were unordered in aqueous medium but had a propensity for a helical structure in trifluoroethanol. However, diastereo analogs were unordered in both aqueous medium and trifluoroethanol. Thus, reversing the sequence in a short amphiphilic peptide may not always result in the selective loss of biological activity such as hemolytic activity. Also, introduction of enantiomeric amino acids in a short peptide to generate a diastereomer may result in loss of structure as well as antimicrobial and hemolytic activities, unless compensated by an increase in positive charges.

Synthesis and conformational studies of peptidomimetics containing furanoid sugar amino acids and a sugar diacid

Furanoid sugar amino acids (1) were synthesized and used as dipeptide isosteres to induce interesting turn structures in small linear peptides. They belong to a new variety of designed hybrid structures that carry both amino and carboxyl groups on rigid furanose sugar rings. Four such molecules, 6-amino-2,5-anhydro-6-deoxy-D-gluconic acid (3, Gaa) and its mannonic (4, Maa), idonic (5, Iaa), and a 3,4-dideoxyidonic (6, ddIaa) congeners were synthesized. The synthesis followed a novel reaction path in which an intramolecular 5-exo S(N)2 opening of the hexose-derived terminal aziridine ring in 2 by the gamma-benzyloxy oxygen with concomitant debenzylation occurred during pyridinium dichromate oxidation of the primary delta-hydroxyl group to carboxyl function, leading to the formation of furanoid sugar amino acid frameworks in a single step. Incorporation of these furanoid sugar amino acids into Leu-enkephalin replacing its Gly-Gly portion gave analogues 8-11. Detailed structural analysis of these molecules by circular dichroism (CD) and various NMR techniques in combination with constrained molecular dynamics (MD) simulations revealed that two of these analogues, 8a and 10a, have folded conformations composed of an unusual nine-membered pseudo beta-turn-like structure with a strong intramolecular H-bond between LeuNH --> sugarC3-OH. This, in turn, brings the two aromatic rings of Tyr and Phe in close proximity, a prerequisite for biological activities of opioid peptides. The analgesic activities of 8a,b determined by mouse hot-plate and tail-clip methods were similar to that of Leu-enkephalin methyl ester. The syn disposition of the beta-hydroxycarboxyl motif on the sugar rings appears to be the driving force to nucleate the observed turn structures in some of these molecules (8 and 10). Repetition of the motif on both sides of a furanose ring resulted in a novel molecular design of sugar diacid, 2,5-anhydro-D-idaric acid (7, Idac). Bidirectional elongation of the diacid moieties of 7 with identical peptide strands led to the formation of a C2-symmetric reverse-turn mimetic 12 which displayed a very ordered structure consisting of identical intramolecular H-bonds at two ends between LeuNH --> sugar-OH, the same as in 8 and 10.

Combinatorial signaling in the specification of unique cell fates

How multifunctional signals combine to specify unique cell fates during pattern formation is not well understood. Here, we demonstrate that together with the transcription factor Lozenge, the nuclear effectors of the EGFR and Notch signaling pathways directly regulate D-Pax2 transcription in cone cells of the Drosophila eye disc. Moreover, the specificity of D-Pax2 expression can be altered upon genetic manipulation of these inputs. Thus, a relatively small number of temporally and spatially controlled signals received by a set of pluripotent cells can create the unique combinations of activated transcription factors required to regulate target genes and ultimately specify distinct cell fates within this group. We expect that similar mechanisms may specify pattern formation in vertebrate developmental systems that involve intercellular communication.

Antibacterial and hemolytic activities of single tryptophan analogs of indolicidin

The structure and biological activities of analogs of the bovine neutrophil antibacterial and hemolytic peptide indolicidin, ILPWKWPWWPWRR-amide, where one tryptophan at 4th, 8th, or 11th position has been retained and the others replaced by leucine, have been investigated. All the single tryptophan analogs exhibit antibacterial activity. However, unlike indolicidin, they do not lyse erythrocytes. Structure analysis by circular dichroism spectroscopy indicates that the analogs are unordered in aqueous medium and adopt beta-turn structures in trifluoroethanol and micelles. The tryptophan residues in indolicidin appear to be essential for hemolytic activity but not antibacterial activity. The nonspecific biological activities of indolicidin and specific antibacterial activity of single tryptophan analogs suggest that in short peptides, a motif composed of hydrophobic amino acids with the exception of tryptophan, interspaced with proline residues and cationic amino acids at the N or C termini would favor selective antibacterial activity.

Double-helical cyclic peptides: design, synthesis, and crystal structure of figure-eight mirror-image conformers of adamantane-constrained cystine-containing cyclic peptide cyclo (Adm-Cyst)(3)

A large number of macrocycles containing alternating repeats of cystine diOMe(-NH-CH(CO(2)Me)-CH(2)-S-)(2) and either a conformationally rigid aromatic/alicyclic moiety or a flexible polymethylene unit (X) in the cyclic backbone with ring size varying from 13- to 78-membered have been examined by spectral ((1)H NMR, FT-IR, CD) and X-ray crystallography studies for unusual conformational preferences. While (1)H NMR measurements indicated a turnlike conformation for all macrocycles, stabilized by intramolecular NH.CO hydrogen bonding, as also supported by FT-IR spectra in chloroform, convincing proof for beta-turn structures was provided by circular dichroism studies. Single-crystal X-ray studies on 39-membered cyclo (Adm-L-Cyst)(3) revealed a double-helical fold (figure-eight motif) for the macrocycle. Only a right-handed double helix was seen in the macrocycle constructed from L-cystine. The mirror-image macrocycle made up of D-cystine units exhibited a double helix with exactly the opposite screw sense, as expected. The enantiomeric figure-eights were stabilized by two intramolecular NH. CO hydrogen bonds and exhibited identical (1) H NMR and FT-IR spectra. The CD spectra of both isomers had a mirror-image relationship. The present results have clearly brought out the importance of cystine residues in inducing turn conformation that may be an important deciding factor for the adoption of topologically important structures by macrocycles containing multiple S-S linkages.

Solid-phase synthesis of a modified 13-residue seminalplasmin fragment on 1,6-hexanediol diacrylate-crosslinked polystyrene support

A novel 1,6-hexanediol diacrylate cross-linked resin was prepared that was subsequently functionalized by using chloromethyl methyl ether to afford a high-capacity resin. The resin exhibited good swelling and its application in the successful synthesis of a 13-residue peptide corresponding to the fragment of seminalplasmin has been illustrated. The resin was chemically inert at peptide synthetic conditions.

Norbornene-constrained cyclic peptides with hairpin architecture: design, synthesis, conformation, and membrane ion transport

A novel family of hairpin cyclic peptides has been designed on the basis of the use of norbornene units as the bridging ligands. The design is flexible with respect to the choice of an amino acid, the ring size, and the nature of the second bridging ligand as illustrated here with the preparation of a large number of norborneno cyclic peptides containing a variety of amino acids in ring sizes varying from 12- to 29-membered, with the choice of the second bridging ligand being a rigid norbornene (11, 13a,b), an adamantane unit (7a,b and 8), or a flexible cystine residue (4a,b and 10). The presence of built-in handles (as protected COOH groups) permits the attachment of a variety of subunits as shown here with the ligation of Leu-Leu, Val-Val, or Aib-Aib pendants in 4b, 7b, and 13b, respectively. This novel class of constrained cyclic peptides are demonstrated to adopt beta-sheet- or hairpin-like conformation as shown by (1)H NMR and CD spectra. Membrane ion-transport studies have shown that the norborneno cyclic peptides 4b and 7b containing Leu-Leu or Val-Val pendants symmetrically placed on the exterior of the ring show high efficiency and selectivity in the transport of specifically monovalent cations. This property can be attributed to the hairpin-like architecture induced by the norbornene unit since the bis-adamantano peptide 15 containing two pairs of Leu-Leu pendants on the exterior is able to transport both monovalent (Na(+), K(+)) and divalent (Mg(2+)/Ca(2+)) cations.

Interaction of antimicrobial peptides with biological and model membranes: structural and charge requirements for activity

Species right across the evolutionary scale from insects to mammals use peptides as part of their host-defense system to counter microbial infection. The primary structures of a large number of these host-defense peptides have been determined. While there is no primary structure homology, the peptides are characterized by a preponderance of cationic and hydrophobic amino acids. The secondary structures of many of the host-defense peptides have been determined by a variety of techniques. The acyclic peptides tend to adopt helical conformation, especially in media of low dielectric constant, whereas peptides with more than one disulfide bridge adopt beta-structures. Detailed investigations have indicated that a majority of these host-defense peptides exert their action by permeabilizing microbial membranes. In this review, we discuss structural and charge requirements for the interaction of endogenous antimicrobial peptides and short peptides that have been derived from them, with membranes.

Conformations of hydrophobic peptides in trifluoroethanol, water and in solid state: a circular dichroism and Fourier Transform Infrared study

The conformations of peptides corresponding to KLLIALVLCFLPLAALG have been examined in trifluoroethanol (TFE), aqueous medium by circular dichroism spectroscopy and in the solid state by Fourier Transform Infra Red Spectroscopy (FTIR). The 17-residue parent peptide and peptides corresponding to shorter segments LVLCFLPLAALG and CFLPLAALG showed preference for helical conformation in TFE. Even the shorter hydrophobic peptides corresponding to KLLIA and LVL showed propensity for beta-turn conformations in TFE. However, peptides corresponding to the relatively polar segment FLPLAALG were unordered in TFE. In water, peptides that showed ordered conformation in TFE preferred beta-conformation. In solid-state, FTIR spectra indicated that the hydrophobic peptides adopt beta-structures with extensive hydrogen bonded network in the solid-state. The hydrophobic core segment thus appears to dictate the conformational propensity of the peptide.

Consequences of introducing a disulfide bond into an antibacterial and hemolytic peptide

The effect of introducing a disulfide bridge between the N- and C-terminal ends on the structure and biological activities of the 13-residue linear peptide PKLLKTFLSKWIG(SPFK), which has both antibacterial and hemolytic activity, have been investigated. The terminal amino acids P and G in SPFK were replaced by cysteines to form a disulfide bridge. The linear peptides C(Acm)KLLKTFLSKWIC(Acm) and C(Acm) KLLKTFLSKWIC(Acm)-amide, where Acm is acetamidomethyl group, showed antibacterial activity but did not possess hemolytic activity unlike SPFK. Introduction of an S-S bridge resulted in enhanced hemolytic activity compared with SPFK. The hemolytic activity was particularly pronounced in the cyclic peptide CKLLKTFLSKWIC-amide. Circular dichroism studies indicate that the cyclic peptides tend to adopt distorted helical structures. The cyclic peptides also have a greater affinity for lipid vesicles, which could be the reason for the effective perturbation of the erythrocyte membrane.

A negatively charged region of the skeletal muscle ryanodine receptor is involved in Ca(2+)-dependent regulation of the Ca(2+) release channel

The ryanodine receptor/Ca(2+) release channels from skeletal (RyR1) and cardiac (RyR2) muscle cells exhibit different inactivation profiles by cytosolic Ca(2+). D3 is one of the divergent regions between RyR1 (amino acids (aa) 1872-1923) and RyR2 (aa 1852-1890) and may contain putative binding site(s) for Ca(2+)-dependent inactivation of RyR. To test this possibility, we have deleted the D3 region from RyR1 (DeltaD3-RyR1), residues 1038-3355 from RyR2 (Delta(1038-3355)-RyR2) and inserted the skeletal D3 into Delta(1038-3355)-RyR2 to generate sD3-RyR2. The channels formed by DeltaD3-RyR1 and Delta(1038-3355)-RyR2 are resistant to inactivation by mM [Ca(2+)], whereas the chimeric sD3-RyR2 channel exhibits significant inactivation at mM [Ca(2+)]. The DeltaD3-RyR1 channel retains its sensitivity to activation by caffeine, but is resistant to inactivation by Mg(2+). The data suggest that the skeletal D3 region is involved in the Ca(2+)-dependent regulation of the RyR1 channel.

Biological activities of C-terminal 15-residue synthetic fragment of melittin: design of an analog with improved antibacterial activity

Melittin, the 26-residue predominant toxic peptide from bee venom, exhibits potent antibacterial activity in addition to its hemolytic activity. The synthetic peptide of 15 residues corresponding to its C-terminal end (MCF), which encompasses its most amphiphilic segment, is now being shown to possess antibacterial activity about 5-7 times less compared to that of melittin. MCF, however, is 300 times less hemolytic. An analog of MCF, MCFA, in which two cationic residues have been transpositioned to the N-terminal region from the C-terminal region, exhibits antibacterial activity comparable to that of melittin, but is only marginally more hemolytic than MCF. The biophysical properties of the peptides, like folding and aggregation, correlate well with their biological properties.

Role of the EGF receptor pathway in growth and patterning of the Drosophila wing through the regulation of vestigial

Growth and patterning of the Drosophila wing disc depends on the coordinated expression of the key regulatory gene vestigial both in the Dorsal-Ventral (D/V) boundary cells and in the wing pouch. We propose that a short-range signal originating from the core of the D/V boundary cells is responsible for activating EGFR in a zone of organizing cells on the edges of the D/V boundary. Using loss-of-function mutations and ectopic expression studies, we show that EGFR signaling is essential for vestigial transcription in these cells and for making them competent to undergo subsequent vestigial-mediated proliferation within the wing pouch.

Synthetic peptides corresponding to the beta-hairpin loop of rabbit defensin NP-2 show antimicrobial activity

Mammalian defensins, a class of antibacterial peptides, are composed of 29-35 amino acids with six cysteines which form three disulfide bonds. Structural studies indicate a triple stranded beta-sheet structure with a well defined beta-hairpin loop at the C-terminal region. It is demonstrated in this report that 18 and 26 residue synthetic peptides corresponding to the beta-hairpin region, constrained by a single disulfide bond, have potent antimicrobial activity without hemolytic activity. Circular dichroism spectroscopy indicates that the single S-S bridge appears to constrain the peptides to a beta-structure. Peptides corresponding to the beta-hairpin region of defensins could thus be attractive candidates as therapeutic agents as well as good model compounds for investigation of the various physiological actions of defensins.

Addition and omission analogs of the 13-residue antibacterial and hemolytic peptide PKLLKTFLSKWIG: structural preferences, model membrane binding and biological activities

The consequences of selective addition or deletion of polar amino acids in a 13-residue antibacterial peptide PKLLKTFLSKWIG on structure, membrane binding and biological activities have been investigated. The variants generated are (a) S and T residues replaced by K, (b) S and T residues deleted individually and together, (c) introduction of two additional K and (d) deletion of L and L with T. In the aqueous environment all the peptides were unordered. In trifluoroethanol, the spectra of peptides belonging to groups (a-c) suggest distorted helical conformation. Peptides in group (d) appear to adopt beta-sheet conformation. The peptides bind to zwitterionic and negatively charged lipid vesicles, although to different extents. With the exception of peptides in group (d), all the other peptides exhibited comparable antibacterial activity against Escherichia coli and Staphylococcus aureus. However, the changes made in the peptides in groups (a-c) resulted in reduction of hemolytic activity compared to the parent peptide. Extent of binding to lipid vesicles composed of phosphatidylcholine and cholesterol appears to correlate with hemolytic activity. It appears that polar and charged residues play a major role in modulating the biological activities of the 13-residue peptide PKLLKTFLSKWIG. The 11-residue peptide-like PKLLKFLKWIG has selective antibacterial activity. Thus, by judicious engineering it should be possible to generate short peptides with selective antibacterial activity.