Molecular design and optimization of hepatic cancer SLP76‐derived PLCγ1 SH3‐binding peptide with the systematic N‐substitution of peptide PXXP motif

The phospholipase Cγ1 (PLCγ1) is essential for T‐cell signaling and activation in hepatic cancer immune response, which has a regulatory Src homology 3 (SH3) domain that can specifically recognize and interact with the PXXP‐containing decapeptide segment (¹⁸⁵QP P VP P QRPM¹⁹⁴, termed as SLP76^185–194 peptide) of adaptor protein SLP76 following T‐cell receptor ligation. The isolated peptide can only bind to the PLCγ1 SH3 domain with a moderate affinity due to lack of protein context support. Instead of the traditional natural residue mutagenesis that is limited by low structural diversity and shifted target specificity, we herein attempt to improve the peptide affinity by replacing the two key proline residues Pro187 and Pro190 of SLP76^185–194 PXXP motif with nonnatural N‐substituted amino acids, as the proline is the only endogenous N‐substituted amino acid. The replacement would increase peptide flexibility but can restore peptide activity by establishing additional interactions with the domain. Structural analysis reveals that the domain pocket can be divided into a large amphipathic region and a small negatively charged region; they accommodate hydrophobic, aromatic, polar, and moderate‐sized N‐substituted amino acid types. A systematic replacement combination profile between the peptide residues Pro187 and Pro190 is created by structural modeling, dynamics simulation, and energetics analysis, from which six improved and two reduced N‐substituted peptides as well as native SLP76^185–194 peptide are identified and tested for their binding affinity to the recombinant protein of the human PLCγ1 SH3 domain using fluorescence‐based assays. Two N‐substituted peptides, SLP76^185–194(N‐Leu187/N‐Gln190) and SLP76^185–194(N‐Thr187/N‐Gln190), are designed to have high potency (K_d = 0.67 ± 0.18 and 1.7 ± 0.3 μM, respectively), with affinity improvement by, respectively, 8.5‐fold and 3.4‐fold relative to native peptide (K_d = 5.7 ± 1.2 μM).     

Mechanism of formation of the C‐terminal β‐hairpin of the B3 domain of the immunoglobulin binding protein G from Streptococcus. III. Dynamics of long‐range hydrophobic interactions

A 20‐residue peptide, IG(42–61), derived from the C‐terminal β‐hairpin of the B3 domain of the immunoglobulin binding protein G from Streptoccocus was studied using circular dichroism, nuclear magnetic resonance (NMR) spectroscopy at various temperatures and by differential scanning calorimetry (DSC). Unlike other related peptides studied so far, this peptide displays two heat capacity peaks in DSC measurements (at a scanning rate of 1.5 deg/min at a peptide concentration of 0.07 mM), which suggests a three‐state folding/unfolding process. The results from DSC and NMR measurements suggest the formation of a dynamic network of hydrophobic interactions stabilizing the structure, which resembles a β‐hairpin shape over a wide range of temperatures (283–313 K). Our results show that IG (42–61) possesses a well‐organized three‐dimensional structure stabilized by long‐range hydrophobic interactions (Tyr50 ··· Phe57 and Trp48 ··· Val59) at T = 283 K and (Trp48 ··· Val59) at 305 and 313 K. The mechanism of β‐hairpin folding and unfolding, as well as the influence of peptide length on its conformational properties, are also discussed. Proteins 2010. © 2009 Wiley‐Liss, Inc.     

Low‐Overpotential Electrocatalytic Water Splitting with Noble‐Metal‐Free Nanoparticles Supported in a sp3 N‐Rich Flexible COF

Covalent organic frameworks (COFs) are crystalline organic polymers with tunable structures. Here, a COF is prepared using building units with highly flexible tetrahedral sp³ nitrogens. This flexibility gives rise to structural changes which generate mesopores capable of confining very small (<2 nm sized) non‐noble‐metal‐based nanoparticles (NPs). This nanocomposite shows exceptional activity toward the oxygen‐evolution reaction from alkaline water with an overpotential of 258 mV at a current density of 10 mA cm^?2. The overpotential observed in the COF‐nanoparticle system is the best in class, and is close to the current record of ≈200 mV for any noble‐metal‐free electrocatalytic water splitting system—the Fe–Co–Ni metal‐oxide‐film system. Also, it possesses outstanding kinetics (Tafel slope of 38.9 mV dec^?1) for the reaction. The COF is able to stabilize such small‐sized NP in the absence of any capping agent because of the COF–Ni(OH)₂ interactions arising from the N‐rich backbone of the COF. Density‐functional‐theory modeling of the interaction between the hexagonal Ni(OH)₂ nanosheets and the COF shows that in the most favorable configuration the Ni(OH)₂ nanosheets are sandwiched between the sp³ nitrogens of the adjacent COF layers and this can be crucial to maximizing their synergistic interactions.     

Epitope analysis of the multiphosphorylated peptide αs1‐casein(59–79)

The multiphosphorylated tryptic peptide α_s1‐casein(59–79) has been shown to be antigenic with anti‐casein antibodies. In an approach to determine the amino acyl residues critical for antibody binding we undertook an epitope analysis of the peptide using overlapping synthetic peptides. With α_s1‐casein(59–79) as the adsorbed antigen in a competitive ELISA only two of five overlapping synthetic peptides at 1 mM significantly inhibited binding of the anti‐casein antibodies. Peptides Glu‐Ser(P)‐Ile‐Ser(P)‐Ser(P)‐Ser(P)‐Glu‐Glu and Ile‐Val‐Pro‐Asn‐Ser(P)‐Val‐Glu‐Glu inhibited antibody binding by 20.0±3.6% and 60.3±7.9%, respectively. The epitope of Glu⁶³‐Ser(P)‐Ile‐Ser(P)‐Ser(P)‐Ser(P)‐Glu‐Glu⁷⁰ was further localised to the phosphoseryl cluster as the peptide Ser(P)‐Ser(P)‐Ser(P) significantly inhibited binding of the anti‐casein antibodies to α_s1‐casein(59–79) by 29.5±7.4%. Substitution of Ser(P)⁷⁵ with Ser⁷⁵ in the second inhibitory peptide Ile‐Val‐Pro‐Asn‐Ser(P)⁷⁵‐Val‐Glu‐Glu also abolished inhibition of antibody binding to α_s1‐casein (59–79) demonstrating that Ser(P)⁷⁵ is also a critical residue for recognition by the antibodies. These data show that the phosphorylated residues in the cluster sequence ‐Ser(P)⁶⁶‐Ser(P)‐Ser(P)⁶⁸ and in the sequence ‐Pro⁷³‐Asn‐Ser(P)‐Val‐Glu⁷⁷‐ are critical for antibody binding to α_s1‐casein(59–79) and further demonstrate that a highly phosphorylated segment of a protein can be antigenic. Copyright © 1999 European Peptide Society and John Wiley & Sons, Ltd.     

Characterization of a type of β‐bend ribbon spiral generated by the repeating (Xaa–Yaa–Aib–Pro) motif: The solution structure of harzianin HC IX,a 14‐residue peptaibol forming voltage‐dependent ion channels

The three‐dimensional solution structure of harzianin HC IX, a peptaibol antibiotic isolated from the fungus Trichoderma harzianum, was determined using CD, homonuclear, and heteronuclear two‐dimensional nmr spectroscopy combined with molecular modeling. This 14‐residue peptide, Ac Aib¹ Asn² Leu³ Aib⁴ Pro⁵ Ala⁶ Ile⁷ Aib⁸ Pro⁹ Iva¹⁰ Leu¹¹ Aib¹² Pro¹³ Leuol¹⁴ (Aib, α‐aminoisobutyric acid; Iva, isovaline; Leuol, leucinol), is a main representative of a short‐sequence peptaibol class characterized by an acetylated N‐terminus, a C‐terminal amino alcohol, and the presence of three Aib‐L ‐Pro motifs at positions 4–5, 8–9, and 12–13, separated by two dipeptide units. In spite of a lower number of residues, compared to the 18/20‐residue peptaibols such as alamethicin, harzianin HC IX exhibits remarkable membrane‐perturbing properties. It interacts with phospholipid bilayers, increasing their permeability and forming voltage‐gated ion channels through a mechanism slightly differing from that proposed for alamethicin. Sequence‐specific ¹H‐ and ¹³C‐nmr assignments and conformational nmr parameters (³J_NHCαH coupling constants, quantitative nuclear Overhauser enhancement data, temperature coefficients of amide and carbonyl groups, NH–ND exchange rates) were obtained in methanol solution. Sixty structures were calculated based on 98 interproton distance restraints and 6 Φ dihedral angle restraints, using high temperature restrained molecular dynamics and energy minimization. Thirty‐seven out of the sixty generated structures were consistent with the nmr data and were convergent. The peptide backbone consists in a ribbon of overlapping β‐turns twisted into a continuous spiral from Asn² to Leuol¹⁴ and forming a 26 Å long helix‐like structure. This structure is slightly amphipathic, with the three Aib–Pro motifs aligned on the less hydrophobic face of the spiral where the Asn² side chain is also present, while the more hydrophobic bulky side chains of leucines, isoleucine, isovaline, and leucinol are located on the concave side. The repetitive (Xaa–Yaa–Aib–Pro) tetrapeptide subunit, making up the peptide sequence, is characterized by four sets of (Φ,Ψ) torsional angles, with the following mean values: Φ_i = −90°, Ψ_i = −27°; Φ_i+1 = −98°, Ψ_i+1 = −17°; Φ_i+2 = −49°, Ψ_i+2 = −50°; Φ_i+3 = −78°, Ψ_i+3 = +3°. We term this particular structure, specifically occurring in the case of (Xaa–Yaa–Aib–Pro)_n sequences, the (Xaa–Yaa–Aib–Pro)‐β‐bend ribbon spiral. It is stabilized by 4 → 1 intramolecular hydrogen bonds and differs from both the canonical 3₁₀‐helix made of a succession of type III β‐turns and from the β‐bend ribbon spiral that has been described in the case of (Aib–Pro)n peptide segments. © 1999 John Wiley & Sons, Inc. Biopoly 50: 71–85, 1999     

Modulation of protein–ligand interactions by photocleavage of a cyclic peptide using phosphatidylinositol 3‐kinase SH3 domain as model system

To photomodulate the interaction of the phosphatidylinositol 3‐kinase SH3 domain with a peptide ligand, a cyclic peptide (cyclic‐1) with a photolabile side chain‐to‐side chain linker was synthesized. The conformation of cyclic‐1 differs from that of the parent linear peptide, but becomes identical by UV‐irradiation. Accordingly, the binding affinity of cyclic‐1 to the SH3 domain increased upon conversion of the cyclic to a linear flexible structure by irradiation (K_d: 3.4 ± 1.7 and 0.9 ± 0.3 mM , respectively). These results confirm the usefulness of a photocleavable peptide for photocontrol of peptide–protein interactions. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd.     

Isostructural unbranched alkyl‐chains as tools for stabilizing β‐turn structure

To investigate the structural role played by isostructural unbranched alkyl‐chains on the conformational ensemble and stability of β‐turn structures, the conformational properties of a designed model peptide: Plm‐Pro‐Gly‐Pda ( 1 , Plm: H₃C—(CH₂)₁₄—CONH—; Pda: —CONH— (CH₂)₁₄—CH₃) have been examined and compared with the parent peptide: Boc‐Pro‐Gly‐NHMe ( 2 , Boc: tert‐butoxycarbonyl; NHMe: N‐methylamide). The characteristic ¹³C NMR chemical‐shifts of the Pro C^β and C^γ resonances ascertained the incidence of an all‐trans peptide‐bond in low polarity deuterochloroform solution. Using FTIR and ¹H NMR spectroscopy, we establish that apolar alkyl‐chains flanking a β‐turn promoting Pro‐Gly sequence impart definite incremental stability to the well‐defined hydrogen‐bonded structure. The assessment of ¹H NMR derived thermodynamic parameters of the hydrogen‐bonded amide‐NHs via variable temperature indicate that much weaker hydrophobic interactions do contribute to the stability of folded reverse turn structures. The far‐UV CD spectral patterns of 1 and 2 in 2,2,2‐trifluoroethanol are consistent with Pro‐Gly specific type II β‐turn structure, concomitantly substantiate that the flanking alkyl‐chains induce substantial bias in enhanced β‐turn populations. In view of structural as well as functional importance of the Pro‐Gly mediated secondary structures, besides biochemical and biological significance of proteins lipidation via myristoylation or palmytoilation, we highlight potential convenience of the unbranched Plm and Pda moieities not only as main‐chain N‐ and C‐terminal protecting groups but also to mimic and stabilize specific isolated secondary and supersecondary structural components frequently observed in proteins and polypeptides. © 2013 Wiley Periodicals, Inc. Biopolymers 99: 419–426, 2013.     

Lipid interactions of acylated tryptophan‐methylated lactoferricin peptides by solid‐state NMR

Lactoferricin (LfB) is a 25‐residue innate immunity peptide released by pepsin from the N‐terminal region of bovine lactoferrin. A smaller amidated peptide, LfB6 (RRWQWR‐NH₂) retains antimicrobial activity and is thought to constitute the “antimicrobial active‐site” (Tomita, Acta Paediatr Jpn. 1994; 36 : 585–91). Here we report on N‐acylation of 1‐Me‐Trp⁵‐LfB6, Cn‐RRWQ[1‐Me‐W]R‐NH₂, where Cn is an acyl chain having n = 0, 2, 4, 6 or 12 carbons. Tryptophan 5 (Trp⁵) was methylated to enhance membrane binding and to allow for selective deuteration at that position. Peptide/lipid interactions of Cn‐RRWQ[1‐Me‐W ]R‐NH₂ (deuterated 1‐Me‐Trp⁵ underlined), were monitored by solid state ³¹P NMR and ²H NMR. The samples consisted of macroscopically oriented bilayers of mixed neutral (dimyristoylphosphatidylcholine, DMPC) and anionic (dimyristoylphosphatidylglycerol, DMPG) lipids in a 3:1 ratio with Cn‐RRWQ[&1‐Me‐W ]R‐NH₂ peptides added at a 1:25 peptide to lipid ratio. ²H‐NMR spectra reveal that the acylated peptides are well aligned in DMPC:DMPG bilayers. The ²H NMR quadrupolar splittings suggest that the 1‐Me‐Trp is located in a motionally restricted environment, indicating partial alignment at the membrane interface. ³¹P‐NMR spectra reveal that the lipids are predominantly in a bilayer configuration, with little perturbation by the peptides. Methylation alone, in C0‐RRWQ[1‐Me‐W ]R‐NH₂, resulted in a 3–4 fold increase in antimicrobial activity against E. coli. N‐acylation with a C12 fatty acid enhanced activity almost 90 fold. Copyright © 2008 European Peptide Society and John Wiley & Sons, Ltd.     

Importance of the interaction protein–protein of the CaM–PDE1A and CaM–MLCK complexes in the development of new anti‐CaM drugs

Protein–protein interactions play central roles in physiological and pathological processes. The bases of the mechanisms of drug action are relevant to the discovery of new therapeutic targets. This work focuses on understanding the interactions in protein–protein–ligands complexes, using proteins calmodulin (CaM), human calcium/calmodulin‐dependent 3′,5′‐cyclic nucleotide phosphodiesterase 1A active human (PDE1A), and myosin light chain kinase (MLCK) and ligands αII–spectrin peptide (αII–spec), and two inhibitors of CaM (chlorpromazine (CPZ) and malbrancheamide (MBC)). The interaction was monitored with a fluorescent biosensor of CaM (hCaM M124C–mBBr). The results showed changes in the affinity of CPZ and MBC depending on the CaM–protein complex under analysis. For the Ca²⁺–CaM, Ca²⁺–CaM–PDE1A, and Ca²⁺–CaM–MLCK complexes, CPZ apparent dissociation constants (K_ds) were 1.11, 0.28, and 0.55 μM, respectively; and for MBC K_ds were 1.43, 1.10, and 0.61 μM, respectively. In competition experiments the addition of calmodulin binding peptide 1 (αII–spec) to Ca²⁺–hCaM M124C–mBBr quenched the fluorescence (K_d = 2.55 ± 1.75 pM) and the later addition of MBC (up to 16 μM) did not affect the fluorescent signal. Instead, the additions of αII–spec to a preformed Ca²⁺–hCaM M124C–mBBr–MBC complex modified the fluorescent signal. However, MBC was able to displace the PDE1A and MLCK from its complex with Ca²⁺–CaM. In addition, docking studies were performed for all complexes with both ligands showing an excellent correlation with experimental data. These experiments may help to explain why in vivo many CaM drugs target prefer only a subset of the Ca²⁺–CaM regulated proteins and adds to the understanding of molecular interactions between protein complexes and small ligands. Copyright © 2013 John Wiley & Sons, Ltd.     

Perfluoro‐tert‐butyl‐homoserine as a sensitive 19F NMR reporter for peptide–membrane interactions in solution

Fluorine (¹⁹F) NMR is a valuable tool for studying dynamic biological processes. However, increasing the sensitivity of fluorinated reporter molecules is a key to reducing acquisition times and accessing transient biological interactions. Here, we evaluate the utility a novel amino acid, l ‐O‐(perfluoro‐t‐butyl)‐homoserine (pFtBSer), that can easily be synthesized and incorporated into peptides and provides greatly enhanced sensitivity over currently used ¹⁹F biomolecular NMR probes. Incorporation of pFtBSer into the potent antimicrobial peptide MSI‐78 results in a sharp ¹⁹F NMR singlet that can be readily detected at concentrations of 5 µm and lower. We demonstrate that pFtBSer incorporation into MSI‐78 provides a sensitive tool to study binding through ¹⁹F NMR chemical shift and nuclear relaxation changes. These results establish future potential for pFtBSer to be incorporated into various proteins where NMR signal sensitivity is paramount, such as in‐cell investigations. Copyright © 2013 European Peptide Society and John Wiley & Sons, Ltd.     

Effects of N‐Acetyl‐L‐Cysteine‐Capped CdTe Quantum Dots on Bovine Serum Albumin and Bovine Hemoglobin: Isothermal Titration Calorimetry and Spectroscopic Investigations

The interactions of N‐acetyl‐L‐cysteine‐capped CdTe quantum dots (QDs) with bovine serum albumin (BSA) and bovine hemoglobin (BHb) were investigated by isothermal titration calorimetry (ITC), fluorescence, synchronous fluorescence, fluorescence lifetime, ultraviolet–visible absorption, and circular dichroism techniques. Fluorescence data of BSA–QDs and BHb–QDs revealed that the quenching was static in every system. While CdTe QDs changed the microenvironment of tryptophan in BHb, the microenvironment of BSA kept unchanged. Adding CdTe QDs affected the skeleton and secondary structure of the protein (BSA and BHb). The ITC results indicated that the interaction between the protein (BSA and BHb) and QDs‐612 was spontaneous and the predominant force was hydrophobic interaction. In addition, the binding constants were determined to be 1.19 × 10⁵ L mol^?1 (BSA–QDs) and 2.19 × 10⁵ L mol^?1 (BHb–QDs) at 298 K. From these results, we conclude that CdTe QDs have a larger impact on the structure of BHb than BSA.     

Quantitative analysis of safranal in saffron extract and nanoparticle formulation by a validated high‐performance thin‐layer chromatographic method†

Introduction – Safranal is an effective anticonvulsant shown to act as an agonist at GABA_A receptors. Nose to brain delivery via nanoparticle formulation might improve its brain delivery. A selective and sensitive analytical method is required for evaluation of safranal‐based novel drug delivery systems. Objective – To develop and validate a high‐performance thin‐layer chromatographic (HPTLC) method for the quantitative analysis of safranal as bulk, in saffron extract and in developed safranal‐loaded nanoparticle formulation. Methodology – Chromatographic separation was achieved on silica gel pre‐coated TLC aluminium plates 60F‐254, using n‐hexane:ethyl acetate (9 : 1, v/v) as the mobile phase. Quantitative analysis was carried out by densitometry at a wavelength of 310 nm. The method was validated and applied to detect related impurities, to analyse safranal in saffron extract and to evaluate safranal‐loaded nanoparticles. Results – Compact spots of safranal were observed at R_f value 0.51 ± 0.02. The method was linear (r = 0.9991) between 0.5 and 5.0 μg/spot. The intra‐ and inter‐day precisions were 1.08–2.17 and 1. 86–3.47%, respectively. The limit of detection was 50 ng/spot and the limit of quantification was 150 ng/spot. The method proved to be accurate (recovery 97.4–102.0%) and was selective for safranal. Evaluation of safranal‐loaded nanoparticle formulation demonstrated drug loading of 23.0%, encapsulation efficiency of 42.0% and sustained drug release following biphasic pattern. Conclusion – The present method is useful for the quantitative and qualitative analysis of safranal and safranal‐loaded nanoparticle formulation. It provides significant advantages in terms of greater specificity and rapid analysis. Copyright © 2009 John Wiley & Sons, Ltd.     

Deletion of the carboxyl‐terminal residue disrupts the amino‐terminal folding,self‐association,and thermal stability of an amphipathic antimicrobial peptide

Understanding the complex relationship between amino acid sequence and protein behaviors, such as folding and self‐association, is a major goal of protein research. In the present work, we examined the effects of deleting a C‐terminal residue on the intrinsic properties of an amphapathic α‐helix of mastoparan‐B (MP‐B), an antimicrobial peptide with the sequence LKLKSIVSWAKKVL‐NH2. We used circular dichroism and nuclear magnetic resonance to demonstrate that the peptide MP‐B^[1‐13] displayed significant unwinding at the N‐terminal helix compared with the parent peptide of MP‐B, as the temperature increased when the residue at position 14 was deleted. Pulsed‐field gradient nuclear magnetic resonance data revealed that MP‐B forms a larger diffusion unit than MP‐B^[1‐13] at all experimental temperatures and continuously dissociates as the temperature increases. In contrast, the size of the diffusion unit of MP‐B^[1‐13] is almost independent of temperature. These findings suggest that deleting the flexible, hydrophobic amino acid from the C‐terminus of MP‐B is sufficient to change the intrinsic helical thermal stability and self‐association. This effect is most likely because of the modulation of enthalpic interactions and conformational freedom that are specified by this residue. Our results implicate terminal residues in the biological function of an antimicrobial peptide. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.     

Determination of manganese‐ and manganese‐containing fungicides with lucigenin–Tween‐20‐enhanced chemiluminescence detection

A flow‐injection (FI) method is reported for the determination of Mn(II), maneb and mancozeb fungicides based on the catalytic effect of Mn(II) on the oxidation of lucigenin and dissolved oxygen in a basic solution. The Tween‐20 surfactant has been reported for first time to enhance lucigenin chemiluminescence (CL) intensity in the presence of Mn(II) (53%) and maneb and mancozeb (89%). The calibration graphs were linear in the concentration range of 0.001–1.5 mg L^–1 (R² = 0.9982 (n = 11) with a limit of detection (S/N = 3) of 0.1 µg L^–1 for Mn(II) and 0.01–3.0 mg L^–1 [R² = 0.9989 and R² = 0.9992 (n = 6)] with a limit of detection (S/N =3) of 1.0 µg L^–1 for maneb and mancozeb respectively. Injection throughputs of 90 and 120 h^–1 for Mn(II) and maneb and mancozeb respectively, and relative standard deviations of 1.0–3.4% were obtained in the concentration range studied. The experimental variables, e.g., reagents concentrations, flow rates, sample volume, and photomultiplier tube voltage, were optimized and potential interferences were investigated. The analysis of Mn(II) in river water reference materials (SLRS‐4 and SLRS‐5) showed good agreement with the certified values incorporating an on‐line 8‐hydroxyquinoline chelating column in the manifold for removing interfering metal ions. Recoveries for maneb and mancozeb were in the range of 92 ± 5 to 104 ± 3% and 91 ± 2 to 100 ± 4% (n = 3) respectively. The effect of 30 other pesticides (fungicides, herbicides and insecticides) was also examined in the lucigenin–Tween‐20 CL system. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of head‐to‐tail cyclization on conformation of histatin‐5

Histatin‐5 (Hst‐5, DSHAKRHHGYKRKFHEKHHSHRGY) is a member of a histidine‐rich peptide family secreted by major salivary glands, exhibiting high fungicidal activity against Candida albicans. In the present work, we demonstrate the 3D structure of the head‐to‐tail cyclic variant of Hst‐5 in TFE solution determined using NMR spectroscopy and molecular dynamics simulations. The cyclic histatin‐5 reveals a helix‐loop‐helix motif with α‐helices at positions Ala⁴‐His⁷ and Lys¹¹‐Ser²⁰. Both helical segments are arranged relative to each other at an angle of ca. 142°. The head‐to‐tail cyclization increases amphipathicity of the peptide, this, however, does not affect its antimicrobial potency. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.     

Ce3+/Tb3+ non‐/single‐/co‐doped K‐Lu‐F materials: synthesis,optical properties,and energy transfer

Using a hydrothermal method, Ce³⁺/Tb³⁺ non‐/single‐/co‐doped K‐Lu‐F materials have been synthesized. The X‐ray diffraction (XRD) results suggest that the Ce³⁺ and/or Tb³⁺ doping had great effects on the crystalline phases of the final samples. The field emission scanning electron microscopy (FE‐SEM) images indicated that the samples were in hexagonal disk or polyhedron morphologies in addition to some nanoparticles, which also indicated that the doping also had great effects on the sizes and the morphologies of the samples. The energy‐dispersive spectroscopy (EDS) patterns illustrated the constituents of different samples. The enhanced emissions of Tb³⁺ were observed in the Ce³⁺/Tb³⁺ co‐doped K‐Lu‐F materials. The energy transfer (ET) efficiency η_T were calculated based on the fluorescence yield. The ET mechanism from Ce³⁺ to Tb³⁺ was confirmed to be the dipole–quadrupole interaction inferred from the theoretical analysis and the experimental data. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and conformational analysis of salivary proline‐rich peptide P‐B

The 57‐amino acid human salivary polypeptide P‐B has been synthesized by the solid‐phase method using 9‐fluorenylmethoxycarbonyl (Fmoc) strategy. The circular dichroism (CD) spectroscopy, Fourier‐transform infrared spectroscopy (FTIR) and molecular modeling methods have been used for conformational studies of P‐B. Examination of the CD spectra of P‐B showed the content of the secondary structure to be independent of temperature over the range 0–60 °C at pH = 7 as well as over the pH range of 2–12 at 37 °C. P‐B adopts predominantly unordered structure with locally appearing β‐turns. The cumulative results obtained using the CD and FTIR spectroscopic techniques indicate the percentage of the polyproline type‐II (PPII) helix being as low as about 10%. Similarly, the molecular dynamics (MD) simulations reveal only a short PPII helix in the C‐terminal fragment of the peptide (Pro⁵¹–Pro⁵⁴), which constitutes 7%. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.     

Atomistic mechanisms of huntingtin N‐terminal fragment insertion on a phospholipid bilayer revealed by molecular dynamics simulations

The huntingtin protein is characterized by a segment of consecutive glutamines (Q_N) that is responsible for its fibrillation. As with other amyloid proteins, misfolding of huntingtin is related to Huntington's disease through pathways that can involve interactions with phospholipid membranes. Experimental results suggest that the N‐terminal 17‐amino‐acid sequence (htt^NT) positioned just before the Q_N region is important for the binding of huntingtin to membranes. Through all‐atom explicit solvent molecular dynamics simulations, we unveil the structure and dynamics of the htt^NTQ_N fragment on a phospholipid membrane at the atomic level. We observe that the insertion dynamics of this peptide can be described by four main steps—approach, reorganization, anchoring, and insertion—that are very diverse at the atomic level. On the membrane, the htt^NT peptide forms a stable α‐helix essentially parallel to the membrane with its nonpolar side‐chains—mainly Leu‐4, Leu‐7, Phe‐11 and Leu‐14—positioned in the hydrophobic core of the membrane. Salt‐bridges involving Glu‐5, Glu‐12, Lys‐6, and Lys‐15, as well as hydrogen bonds involving Thr‐3 and Ser‐13 with the phospholipids also stabilize the structure and orientation of the htt^NT peptide. These observations do not significantly change upon adding the Q_N region whose role is rather to provide, through its hydrogen bonds with the phospholipids' head group, a stable scaffold facilitating the partitioning of the htt^NT region in the membrane. Moreover, by staying accessible to the solvent, the amyloidogenic Q_N region could also play a key role for the oligomerization of htt^NTQ_N on phospholipid membranes. Proteins 2014; 82:1409–1427. © 2014 Wiley Periodicals, Inc.     

Influence of thiol capping on the photoluminescence properties of L‐cysteine‐, mercaptoethanol‐ and mercaptopropionic acid‐capped ZnS nanoparticles

Mercaptoethanol (ME), mercaptopropionic acid (MPA) and L‐cysteine (L‐Cys) having ‐SH functional groups were used as surface passivating agents for the wet chemical synthesis of ZnS nanoparticles. The effect of the thiol group on the optical and photoluminescence (PL) properties of ZnS nanoparticles was studied. L‐Cysteine‐capped ZnS nanoparticles showed the highest PL intensity among the studied capping agents, with a PL emission peak at 455 nm. The PL intensity was found to be dependent on the concentration of Zn²⁺ and S^2– precursors. The effect of buffer on the PL intensity of L‐Cys‐capped ZnS nanoparticles was also studied. UV/Vis spectra showed blue shifting of the absorption edge. Copyright © 2015 John Wiley & Sons, Ltd.     

Stopped‐flow chemiluminescence determination of the anticancer drug capecitabine: Application in pharmaceutical analysis and drug‐delivery systems

Capecitabine is a chemotherapeutic agent used for the treatment of patients with metastatic cancers. This study aimed at determining the drug capecitabine in a simple chemiluminescence (CL) system of acidic potassium permanganate using the stopped‐flow injection technique. Statistical methods were used to detect optimum conditions. The method showed two linear calibration ranges from 6.7 × 10^?6 to 6.7 × 10^?5 mol L^?1 and from 6.7 × 10^?5 to 2.7 × 10^?3 mol L^?1 with a detection limit of 1.5 × 10^?6 mol L^?1. Chitosan‐modified magnetic nanoparticles were studied in the drug‐delivery experiments. According to the pH sensitivity of chitosan and low pH values in tumour cells, the chitosan‐coated magnetic nanoparticles could provide a good targeting drug‐delivery system to tumour sites. To evaluate the applicability of the method, the capecitabine‐loaded magnetic chitosan nanoparticles were synthesized with two different cross‐linkers; loading and releasing rates of the drug were investigated using the proposed CL method and an ultraviolet–visible light spectrophotometric method (absorption at 305 nm). The results showed a good correlation between the two methods, and it was found that the synthesized chitosan‐modified magnetic nanoparticles could be used for pH‐dependent release of capecitabine in cancer cells. Moreover, determination of capecitabine in tablets and synthetic samples was performed.