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Axel Schulz

Publications and source records attributed to Axel Schulz.

At least 19 recordsLinked to original sources
PubMed2006

The novel beta-defensin DEFB123 prevents lipopolysaccharide-mediated effects in vitro and in vivo.

Defensins are a family of secreted antimicrobial peptides proposed to directly interfere with bacterial membranes. Here we show a functional analysis of the novel beta-defensin DEFB123. A peptide comprising the beta-defensin core region was synthesized and used for our analysis. Like other beta-defensins, DEFB123 exerted antimicrobial activity against a broad spectrum of Gram-positive and Gram-negative bacteria, which was assessed by microbroth dilution assay and radial diffusion zone assay. In addition, the peptide showed lipopolysaccharide (LPS)-binding activity in a Limulus amoebocyte lysate (LAL) assay. Moreover, DEFB123 prevented LPS-induced tumor necrosis factor (TNF)-alpha secretion in a murine monocyte cell line (RAW264.7). Accordingly, DEFB123 abolished LPS-mediated MAPK induction in these cells. Protection against LPS-mediated effects was then investigated in a murine model of acute sepsis. Our experiments show that synthetic beta-defensin DEFB123 prevents LPS-induced mortality in C57BL/6 mice in a therapeutic approach. We propose that the physiological role of beta-defensins may include interference with LPS-action on macrophages, a function formerly thought to be restricted to the family of cathelicidins, a structurally unrelated group of antimicrobial peptides.

Animals↗
PubMed2006

Synthesis and structure-activity relationship of beta-defensins, multi-functional peptides of the immune system.

beta-defensins are a large family of multiple disulfide-bonded peptides occurring in mammals and birds. They play an important role in the innate immune system, directly killing microbial organisms. Recent research has demonstrated that beta-defensins are important for other biological functions beyond antimicrobial effects, including inhibition of viral infection, interaction with Toll-like receptors, chemotactic effects, and sperm function. The corresponding broad spectrum of activities makes this peptide class an important subject and tool in immunologic research. In this review, we summarize the current status of the routes to obtain synthetic beta-defensins, their major structural properties and structure-activity relationship.

Amino Acid Sequence↗
PubMed2005

Preoperative concentration of beta-lipotropin immunoreactive material in cerebrospinal fluid: a predictor of postoperative pain?

Levels of beta-endorphin immunoreactive material (IRM) in cerebrospinal fluid (CSF) have been reported to correlate inversely with postoperative morphine requirement. Considering proopiomelanocortin (POMC) derivatives as predictors for sensitivity to postoperative pain, we determined authentic beta-endorphin (beta-endorphin(1-31)), beta-lipotropin IRM, N-acetyl-beta-endorphin IRM and ACTH in CSF of 17 patients undergoing hip or knee arthroplasty, before surgery (t(A)), immediately after termination of propofol infusion and still under spinal anesthesia (t(B)), under postoperative pain (t(C)) and one day after surgery (t(D)); patients rated their severity of pain on a visual analogue scale (VAS) at those four times. In all patients CSF concentrations of N-acetyl-beta-endorphin IRM and beta-lipotropin IRM were found to be increased after terminating the propofol infusion with spinal anesthesia still effective at t(B). Patients did not feel pain at times t(A), t(B) or t(D); however, they reported moderate to considerable pain at t(C). There were no correlations of postoperative pain severity at t(C) with ACTH, beta-endorphin(1-31) or N-acetyl-beta-endorphin IRM concentrations in CSF. In contrast, we observed significant inverse correlations (Spearman's rank correlation coefficients between -0.83 and -0.85, p<0.01) for postoperative pain severity with beta-lipotropin IRM concentrations in CSF at t(C), and, in addition, at t(A), t(B) and t(D); thus, postoperative pain severity appeared to be dependent on a central system controlling sensitivity to pain, linked to a POMC system releasing beta-lipotropin IRM into CSF and already active at times t(A) and t(B). We conclude that beta-lipotropin IRM in CSF might be considered to serve as a predictor of sensitivity to postoperative pain.

Arthroplasty, Replacement, Hip↗
PubMed2005

3,5-Dimethyl-1,3,5-oxadiazane-2,4,6-trione: short intermolecular contacts determining the crystal packing.

In the title compound, C5H6N2O4, the molecules lie across a crystallographic mirror plane. The compound lacks traditional hydrogen-bond donors, and hence crystals are held together by unusual C=O...O, O...C and weak C-H...O interactions, forming layers. Adjacent layers are arranged in an antiparallel manner, yielding an ABA layer sequence. The intermolecular contacts are quite short; a topological analysis of charge density based on density-functional-theory calculations was used for consideration of these short contacts and indicated a strong attractive bonding closed-shell interaction between these atoms in the crystal structure.

Journal Article↗
PubMed2005

The dianion of 5-cyanoiminotetrazoline: C2N62-.

Several salts (alkali, Pd(NH(3))(3), and (i)PrNH(2)) of 5-cyanoiminotetrazoline (C(2)N(6)(2-), 5-cyanoiminotetrazolinediide, CIT) were investigated. A full characterization by means of X-ray, Raman, NMR techniques, mass spectrometry, and elemental analysis is presented for the (i)()PrNH(2) (4), Cs (5), and Pd(NH(3))(3) (6) salts. The CIT dianion represents a nitrogen-rich binary CN dianion, and 5 forms monoclinic crystals (a = 7.345(2) Angstroms, b = 9.505(2) Angstroms, c = 10.198(2) Angstroms, beta = 92.12(3) degrees, space group P2(1)/n, Z = 4). DSC and in situ temperature-dependent X-ray diffraction measurements of the cesium salt 5 revealed an astonishing thermal stability accompanied by a reversible phase transition from the low-temperature alpha modification to the metastable beta modification at 253 degrees C. Above the melting point (334 degrees C), the cesium salt decomposes yielding cesium azide and cesium dicyanamide, which decomposes under further heating under release of nitrogen. The reaction of Cs(2)CIT with SO(2) resulted in the surprising formation of a new cesium salt with the 5-cyaniminotetrazoline-1-sulfonate dianion (Cs(2)CITSO(3).SO(2) (7)). 7 crystallizes in the monoclinic space group P2(1) with one SO(2) solvent molecule (a = 8.0080(2) Angstroms, b = 8.0183(2) Angstroms, c = 9.8986(3) Angstroms, beta = 108.619(1) degrees, Z = 2). The structure and bonding of the 10pi dianion are discussed on the basis B3LYP/aug-cc-pvTZ computations (MO, NBO), and the three-dimensional array of the cesium salts with respect to the Cs(delta) (+)-N(delta)(-) in 5 compared to the Cs(delta)(+)-N(delta)(-) and Cs(delta)(+)-O(delta)(-) in 7 is discussed. Due to the expected rich bonding modes of the CIT anions, the coordination chemistry with palladium was also studied, yielding monoclinic crystals of [Pd(CIT)(NH(3))(3)].H(2)O (6, a = 7.988(2) Angstroms, b = 8.375(2) Angstroms, c = 13.541(3) Angstroms, beta = 104.56 degrees, space group P2(1)/n, Z = 4). In the solid state, the complex is composed of dimers, showing two agostic interactions and an unusual close interplanar pi-pi stacking of the tetrazole moiety of the CIT ligand.

Journal Article↗
PubMed2005

Structure and bonding in silver halides. A quantum chemical study of the monomers: Ag(2)X, AgX, AgX(2), and AgX(3) (X = F, Cl, Br, I).

The molecular structure of all silver halide monomers, Ag(2)X, AgX, AgX(2), and AgX(3), (X = F, Cl, Br, I), have been calculated at the B3LYP, MP2, and CCSD(T) levels of theory by using quasirelativistic pseudopotentials for all atoms except fluorine and chlorine. All silver monohalides are stable molecules, while the relative stabilities of the subhalides, dihalides, and trihalides considerably decrease toward the larger halogens. The ground-state structure of all Ag(2)X silver subhalides has C(2)(v)() symmetry, and the molecules can be best described as [Ag(2)](+)X(-). Silver dihalides are linear molecules; AgF(2) has a (2)Sigma(g) ground state, while all of the other silver dihalides have a ground state of (2)Pi(g) symmetry. The potential energy surface (PES) of all silver trihalides has been investigated. Neither of these molecules has a D(3)(h)() symmetric trigonal planar geometry, due to their Jahn-Teller distortion. The minimum energy structure of AgF(3) is a T-shaped structure with C(2)(v)() symmetry. For AgCl(3), AgBr(3), and AgI(3), the global minimum is an L-shaped structure, which lies outside the Jahn-Teller PES. This structure can be considered as a donor-acceptor system, with X(2) acting as donor and AgX as acceptor. Thus, except for AgF(3), in the other three silver trihalides, silver is not present in the formal oxidation state 3.

Journal Article↗
PubMed2005

In vitro degradation of the antimicrobial human peptide HEM-gamma 130-146 in plasma analyzed by a validated quantitative LC-MS/MS procedure.

In stability studies during preclinical drug development, the human antimicrobial peptide hHEM-gamma 130-146 shows progressive N-terminal degradation in plasma. To determine this effect, we developed and validated a selective and quantitative muHPLC-MS/MS procedure for this compound. Following deproteinization by precipitation, reversed-phase separation is performed with a time-saving two-column design online coupled to an ion trap mass spectrometer for electrospray ionization MS detection. Using a linear calibration curve obtained with synthetic external standards ranging nearly two orders of magnitude, we achieved good precision (repeatability and reproducibility: 5-15%), accuracy (-3 to 15%), and ruggedness with a lower limit of quantification at 0.29 microg/ml plasma (0.15 microM). Because of good linearity (r2>0.999), the recovery (84+/-3%) and ion suppression (86+/-4% remaining intensity) were calculated from specifically prepared calibration curves. The developed procedure was applied to human and animal plasma samples. Incubations in the presence and absence of proteinase inhibitors revealed at least an aminopeptidase M activity for the initial N-terminal truncation of tryptophan (W130) and a putative glutaminyl-peptide cyclotransferase activity for the resulting intermediate starting with the bared glutamine residue (Q131). The calculated periods of half-change demonstrated exceeding interspecies variations, whereas the intraspecies variations were only between 20 and 30%. The current procedure is valuable as a generic method for pharmaceutical purposes, and data give important information for further development toward a potential natural drug candidate.

Amino Acid Sequence↗
PubMed2005

Mono-, di-, and tricoordinated phosphorus attached to a N-N unit: an experimental and theoretical study.

N,N',N'-[Tris(trimethylsilyl)]hydrazino-diphenylphosphane, (TMS)2 N-(TMS)N-PPh2 (1), and N,N',N'-[tris(trimethylsilyl)]hydrazino-phenyl(chloro)phosphane, (TMS)2 N-(TMS)N-P(Cl)Ph2 (2), were obtained in the reaction of bis-[lithium-tris(trimethylsilyl)hydrazide] with Ph(n)PCl(3 - n) (n = 1, 2). The structure and bonding of both species are discussed on the basis of experimentally observed (X-ray, Raman, NMR, and MS) and theoretically obtained data (B3LYP/6-31G(d,p), NBO analysis). Oxidation with sulfur and selenium results in the formation of (TMS)2 N-(TMS)N-P(S)Ph2 (4), (TMS)2 N-(TMS)N-P(Se)Ph2 (5), (TMS)2 N-(TMS)N-P(S)Ph(Cl) (6), and (TMS)2 N-(TMS)N-P(Se)Ph(Cl) (7). Moreover, the thermal decomposition of N,N',N'-[tris(trimethylsilyl)]hydrazine-dichlorophosphane, (TMS)2 N-(TMS)N-PCl2 (3) and the reaction with magnesium have been investigated. The formation and molecular structure of the novel MgCl2(THF)2 x 2Mg[(TMS)NP(O)2 N(TMS)2](THF) (8) salt containing the hitherto unknown (TMS)NP(O)2 N(TMS)2(2-) anion are discussed. DFT calculations (B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d,p)) are used to evaluate the bonding, ground-state structures, and energy landscape for the different isomers of 3: the thermodynamics and kinetics of the successive elimination of chlorotrimethylsilane (TMS-Cl) resulting in the formation of covalent azide analogues such as TMS-PNN or TMS-NNP.

Journal Article↗
PubMed2005

1,5-diamino-4-methyltetrazolium dinitramide.

The highly friction-sensitive 1,5-diamino-4-methyltetrazolium dinitramide was synthesized by a metathetical reaction of the corresponding iodide and silver dinitramide. An intriguing interaction of one nitro group with the tetrazolium cation was found as a crystal structure determining feature (X-ray determination), and the chemical bond is discussed on the basis of the theory of atoms in molecules (AIM).

Journal Article↗
PubMed2005

Blue alkali dinitrosomethanides: synthesis, structure, and bonding.

Explosive alkali dinitrosomethanides (M[HC(NO)2]; M = Li, Na, K, Cs) were prepared in a new, simple, high-yielding synthetic procedure, fully characterized, and shown to be stable at ambient temperature. Alkali dinitrosomethanides are of widespread interest to pharmaceutical and materials scientists alike.

Journal Article↗
PubMed2005

Isolation and characterization of a novel proopiomelanocortin-derived peptide from hemofiltrate of chronic renal failure patients.

We report the isolation of a novel human circulating proopiomelanocortin-derived peptide, VA-beta-MSH, from hemofiltrate and its pharmacological characterization. Screening for lipolytic activity in differentiated 3T3-L1 adipocytes led to the isolation from a hemofiltrate peptide library by alternating reverse phase and cation exchange chromatography. In the course of this isolation, we also identified human beta-MSH-(1-22). We synthesized VA-beta-MSH by the N-(9-fluorenyl)-methoxycarbonyl (F-moc) solid phase method and used synthetic beta-MSH-(1-22) to confirm that both isolated peptides are lipolytically active in a dose-dependent manner in differentiated 3T3-L1 adipocytes in the nanomolar range. Using cAMP ELISA, we demonstrate that stimulation with both peptides caused a strong cAMP elevation in this cell system. Furthermore, we show that the selective inhibitors of cAMP-dependent protein kinase, 8-(4-Chlorophenylthio)adenosine-3',5'-cyclic monophosphorothioate, Rp-isomer (Rp-8-CPT-cAMPS); N-[2-(p-Bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H89), significantly reduce VA-beta-MSH- and beta-MSH-(1-22)-mediated lipolysis. Although isolated after its lipolytic activity on 3T3-L1 cells, this newly identified circulating human melanocortin may serve other functions in human physiology. Moreover, the fact that these peptides have been identified after a functional assay, but have been overseen in large proteomic approaches, underscores the importance of such approaches in identifying previously undescribed circulating bioactive molecules.

3T3-L1 Cells↗
PubMed2005

Engineering disulfide bonds of the novel human beta-defensins hBD-27 and hBD-28: differences in disulfide formation and biological activity among human beta-defensins.

Human beta-defensins comprise a large number of peptides that play a functional role in the innate and adaptive immune system. Recently, clusters of new beta-defensin genes with predominant expression in testicular tissue have been discovered on different chromosomes by bioinformatics. beta-Defensins share a common pattern of three disulfides that are essential for their biological effects. Here we report for the first time the chemical synthesis of the new fully disulfide-bonded beta-defensins hBD-27 and hBD-28, and compare the results with synthetic procedures to obtain the known hBD-2 and hBD-3. While hBD-27 was readily converted into a product with the desired disulfide pattern by oxidative folding, hBD-28 required a selective protective group strategy to introduce the three disulfide bonds. The established synthetic processes were applied to the synthesis of hBD-2, which, like hBD-27, was accessible by oxidative folding, whereas hBD-3 required a selective strategy comparable to hBD-28. Experimental work demonstrated that trityl, acetamidomethyl, and t-butyl are superior to other protection strategies. However, the suitable pairwise arrangement of the protective groups can be different, as shown here for hBD-3 and hBD-28. Determination of the minimum inhibitory concentration against different bacteria revealed that hBD-27, in contrast to other beta-defensins tested, has virtually no antimicrobial activity. Compared to the other peptides tested, hBD-27 showed almost no cytotoxic activity, measured by hemoglobin release of erythrocytes. This might be due to the low positive net charge, which is significantly higher for hBD-2, hBD-3, and hBD-28.

Amino Acid Sequence↗
PubMed2005

Side chain contributions to the interconversion of the topological isomers of guanylin-like peptides.

The peptide hormones guanylin and uroguanylin are ligands of the intestinal guanylyl cyclase-C (GC-C) that is involved in the regulation of epithelial water and electrolyte transport. The small peptides contain 15 and 16 amino acids, respectively, and two disulfide bonds with a 1-3/2-4 connectivity. This structural feature causes the unique existence of two topological isoforms for each peptide in an approximate 3:2 ratio, with only one of the isoforms exhibiting GC-C-activating potential. The two uroguanylin isomers can be separated by HPLC and are of sufficient stability to be studied separately at ambient temperatures while the two guanylin isomers are rapidly interconverting even at low temperatures. Both isomers show clearly distinguishable (1)H chemical shifts. To investigate the influence of certain amino acid side chains on this isomerism and interconversion kinetics, derivatives of guanylin and uroguanylin (L-alanine scan and chimeric peptides) were designed and synthesized by Fmoc solid-phase chemistry and compared by HPLC and 2D (1)H NMR spectroscopy. Amino acid residues with the most significant effects on the interconversion kinetics were predominantly identified in the COOH-terminal part of both peptides, whereas amino acids in the central part of the peptides only moderately affected the interconversion. Thus, the conformational conversion among the isomers of both peptides is under the control of a COOH-terminal sterical hindrance, providing a detailed model for this dynamic isomerism. Our results demonstrate that kinetic control of the interconversion process can be achieved by the introduction of side chains with a defined sterical profile at suitable sequence positions. This is of potential impact for the future development of GC-C peptide agonists and antagonists.

Amino Acid Sequence↗
PubMed2004

Role of disulfide bonds for the structure and folding of proguanylin.

The intestinal peptide hormone guanylin circulates mainly as its corresponding prohormone of 94 amino acids and is the first identified endogenous ligand of intestinal guanylyl cyclase C. While the prohormone is biologically inactive, it is processed to the fully functional form with 15 amino acid residues corresponding to the COOH terminus of the precursor protein. In addition to this inactivation of the hormone region, the prosequence makes an essential contribution to the disulfide-coupled folding of the hormone. On the basis of the recently determined solution structure of proguanylin, explanations for these functions of the prosequence were found, indicating that interstrand contacts between the NH2-terminal beta-hairpin of the prosequence and the COOH-terminal hormone region are crucial for formation of the correct disulfide bonds of guanylin. To further investigate the role of individual disulfide bonds upon stabilization of the overall three-dimensional structure of proguanylin and to test the assumption of a direct effect of the prosequence on the structure of the hormone region, we studied the cysteine double mutant proteins proguanylin-C48S/C61S and proguanylin-C86S/C94S. Disulfide determination as well as CD and NMR spectroscopy of proguanylin-C48S/C61S reveals an essential function of the Cys48-Cys61 disulfide bond for the stability of the hydrophobic core and thereby for the stability of the overall three-dimensional structure of proguanylin. Furthermore, sequence specific resonance assignment of the second disulfide deletion mutant, proguanylin-C86S/C94S, and comparison of the NMR spectra of this protein with those of the wild-type protein demonstrate that the rigid helical core structure of proguanylin is not affected by the mutation. Additionally, analysis of the interstrand contacts between the termini reveals a direct effect of the prosequence on the conformation of the hormone region. On the basis of these results, we propose a cooperative mechanism that leads to formation of the correct disulfide pattern of guanylin.

Amino Acid Sequence↗
PubMed2004

Dimeric (tris(tert-butyl)silyl)phosphanyl (tris(tert-butyl)silyl)phosphanediyl gallane: a molecule with a Ga-P-Ga heteroallyl system.

The metathesis reaction of potassium (tris(tert-butyl)silyl)phosphanide with GaCl(3) in a molar ratio of 1:1 leads to the formation of [Cl(2)GaP(H)Si(t)Bu(3)](2) (1) as a mixture of cis and trans isomers with very large (1)J(P,H) and (2)J(P,P) coupling constants. The molecular structure of 1 shows a Ga(2)P(2) cycle with nearly planar coordinated phosphorus atoms under neglection of the hydrogen atoms and Ga-P distances of 239 pm. The reaction of GaCl(3) with 3 equiv of potassium (tris(tert-butyl)silyl)phosphanide as well as the reaction of 1 with 2 equiv of KP(H)Si(t)Bu(3) yields [(t)Bu(3)SiP(H)Ga(mu-PSi(t)Bu(3))](2) (2). The central moiety comprises a four-membered Ga(2)P(2) cycle with one planar P atom and extremely short Ga-P bonds of approximately 226 pm, the other being in a pyramidal environment with an angle sum of 298.4 degrees. The structure of 2 can be described as a GaPGa heteroallyl system which is bonded to a phosphanidyl substituent. This idea and its dependency on the steric demand of the trialkylsilyl groups are investigated by DFT calculations on different isomers of 2.

Journal Article↗