Natural Peptides with Antimicrobial Activity

Antibiosis is a mechanism by which many cell types control potential environmental takeover or pathogenicity by microbes, especially bacteria. It is now clear that a large proportion of the antimicrobial compounds produced by various cells and organisms including bacteria, fungi, plants, insects, amphibia and mammals are antibiotics based around peptides. These antimicrobial peptides can be broadly subdivided into two groups: those which are produced by multienzyme complexes and those which are encoded by a structural gene, the transcription and translation of which results in a peptide template which may (in some cases) undergo further enzymatic modifications. In this context, the chemistry, biosynthesis and functional aspects of a broad range of bioactive peptides from both subgroups will be briefly discussed, including: gramicidin, bacitracin, valinomycin, alamethicin and polymixin B from the first group, and defensins (and related peptides), bacteriocins, lantibiotics and microcins from the second subgroup. From a biotechnological perspective, the peptide antibiotics produced by multienzyme complexes are open to a variety of manipulations to produce novel antibiotic compounds, whilst the ribosomally synthesised peptides may be specifically altered by site-directed mutagenesis. Furthermore, the enzymes capable of transforming some ribosomally synthesised peptide antibiotics may be of particular interest to the biotechnologist, because of the novel transformations of peptide substrates which they are able to perform

Structure of the pheromone peptide of the Staphylococcus epidermidis agr system

AbstractThe agr quorum-sensing system is responsible for the regulation of several virulence factors in staphylococci, with an extracellular pheromone peptide as signalling molecule. By monitoring the biological activity of synthetic peptides, it could be demonstrated that the pheromone of the agr system in Staphylococcus epidermidis is an octapeptide containing a thiolester linkage between the central cysteine and the C-terminal carboxyl group. The peptide was active at nanomolar concentrations. The N-terminus of the peptide pheromone, which is encoded as part of a protein precursor, proved to be crucial for biological activity

Charakterisierung einer Triazin-Bibliothek mittels markierungsfreier HTS-Reflektometrischen Interferenzspektroskopie

Mittels kombinatorischer Chemie werden heute große Substanzbibliotheken organischer und bioorganischer Verbindungen hergestellt. Eine der Standardmethoden ist die Synthese an festen Phasen. Beim Screening solcher Bibliotheken auf Aktivität gegenüber einem bestimmten Target bieten solche Verfahren einen Vorteil, die die Aktivitätsbestimmung, direkt an der festen Phase erlauben und somit das aufwendige Abspalten und Aufreinigen der großen Zahl an Einzelsubstanzen von der Festphase ersparen. Zur Realisierung eines solchen Systems wurde die Festphasensynthese einer Bibliothek in modifizierten Mikrotiterplatten durchgeführt. Die Böden solcher Mikrotiterplatten bestehen aus einer dünnen SiO2-Schicht, die auf eine Glassubstrat aufgetragen wurde. Eine Modifikation der SiO2-Schicht mit funktionellen Polymeren und das Einbringen einer Ankergruppe ermöglichen die Festphasensynthese. Darüber hinaus ist die Detektion von biomolekularer Wechselwirkung der fixierten Substanzen mit den zugehörigen Targets mit Hilfe der Reflektometrischen Interferenzspektroskopie von der Plattenunterseite erlaubt. Durch die Polymerschicht wird die zur Testung notwendige Biokompatibilität gewährleistet

Video-based, student tutor- versus faculty staff-led ultrasound course for medical students - a prospective randomized study

Background Ultrasound education is propagated already during medical school due to its diagnostic importance. Courses are usually supervised by experienced faculty staff (FS) with patient bedside examinations or students among each other but often overbooked due to limited FS availability. To overcome this barrier, use of teaching videos may be advantageous. Likewise, peer teaching concepts solely with trained student tutors have shown to be feasible and effective. The aim was to evaluate 1) objective learning outcomes of a combined video-based, student-tutor (ViST) as compared to a FS-led course without media support, 2) acceptance and subjective learning success of the videos. Methods Two ultrasound teaching videos for basic and advanced abdominal ultrasound (AU) and transthoracic echocardiography (TTE) were produced and six students trained as tutors. Fourth-year medical students (N = 96) were randomized to either the ViST- or FS course (6 students per tutor). Learning objectives were defined equally for both courses. Acquired practical basic and advanced ultrasound skills were tested in an objective structured clinical examination (OSCE) using modified validated scoring sheets with a maximum total score of 40 points. Acceptance and subjective learning success of both videos were evaluated by questionnaires based on Kirkpatrick's evaluation model with scale-rated closed and open questions. Results 79 of 96 medical students completed the OSCE and 77 could be finally analyzed. There was no significant difference in the mean total point score of 31.3 in the ViST (N = 42) and 32.7 in the FS course (N = 35, P = 0.31) or in any of the examined basic or advanced ultrasound skill subtasks. Of the 42 ViST participants, 29 completed the AU and 27 the TTE video questionnaire. Acceptance and subjective learning success of both videos was rated positively in 14-52% and 48-88% of the rated responses to each category, respectively. Attendance of either the student or faculty tutor was deemed necessary in addition to the videos. Conclusions A ViST versus FS teaching concept was able to effectively teach undergraduate students in AU and TTE, albeit acceptance of the teaching videos alone was limited. However, the ViST concept has the potential to increase course availability and FS resource allocation

Characterization of the ribonuclease activity on the skin surface

The rapid degradation of ribonucleic acids (RNA) by ubiquitous ribonucleases limits the efficacy of new therapies based on RNA molecules. Therefore, our aim was to characterize the natural ribonuclease activities on the skin and in blood plasma i.e. at sites where many drugs in development are applied. On the skin surfaces of Homo sapiens and Mus musculus we observed dominant pyrimidine-specific ribonuclease activity. This activity is not prevented by a cap structure at the 5'-end of messenger RNA (mRNA) and is not primarily of a 5'- or 3'-exonuclease type. Moreover, the ribonuclease activity on the skin or in blood plasma is not inhibited by chemical modifications introduced at the 2'OH group of cytidine or uridine residues. It is, however, inhibited by the ribonuclease inhibitor RNasin(® )although not by the ribonuclease inhibitor SUPERase· In™. The application of our findings in the field of medical science may result in an improved efficiency of RNA-based therapies that are currently in development

Cholestenoic acid, an endogenous cholesterol metabolite, is a potent γ-secretase modulator.

BackgroundAmyloid-β (Aβ) 42 has been implicated as the initiating molecule in the pathogenesis of Alzheimer's disease (AD); thus, therapeutic strategies that target Aβ42 are of great interest. γ-Secretase modulators (GSMs) are small molecules that selectively decrease Aβ42. We have previously reported that many acidic steroids are GSMs with potencies ranging in the low to mid micromolar concentration with 5β-cholanic acid being the most potent steroid identified GSM with half maximal effective concentration (EC50) of 5.7 μM.ResultsWe find that the endogenous cholesterol metabolite, 3β-hydroxy-5-cholestenoic acid (CA), is a steroid GSM with enhanced potency (EC50 of 250 nM) relative to 5β-cholanic acid. CA i) is found in human plasma at ~100-300 nM concentrations ii) has the typical acidic GSM signature of decreasing Aβ42 and increasing Aβ38 levels iii) is active in in vitro γ-secretase assay iv) is made in the brain. To test if CA acts as an endogenous GSM, we used Cyp27a1 knockout (Cyp27a1-/-) and Cyp7b1 knockout (Cyp7b1-/-) mice to investigate if manipulation of cholesterol metabolism pathways relevant to CA formation would affect brain Aβ42 levels. Our data show that Cyp27a1-/- had increased brain Aβ42, whereas Cyp7b1-/- mice had decreased brain Aβ42 levels; however, peripheral dosing of up to 100 mg/kg CA did not affect brain Aβ levels. Structure-activity relationship (SAR) studies with multiple known and novel CA analogs studies failed to reveal CA analogs with increased potency.ConclusionThese data suggest that CA may act as an endogenous GSM within the brain. Although it is conceptually attractive to try and increase the levels of CA in the brain for prevention of AD, our data suggest that this will not be easily accomplished

Imported lassa fever in Germany: molecular characterization of a new lassa virus strain.

We describe the isolation and characterization of a new Lassa virus strain imported into Germany by a traveler who had visited Ghana, Côte D'Ivoire, and Burkina Faso. This strain, designated "AV," originated from a region in West Africa where Lassa fever has not been reported. Viral S RNA isolated from the patient's serum was amplified and sequenced. A long-range reverse transcription polymerase chain reaction allowed amplification of the full-length (3.4 kb) S RNA. The coding sequences of strain AV differed from those of all known Lassa prototype strains (Josiah, Nigeria, and LP) by approximately 20%, mainly at third codon positions. Phylogenetically, strain AV appears to be most closely related to strain Josiah from Sierra Leone. Lassa viruses comprise a group of genetically highly diverse strains, which has implications for vaccine development. The new method for full-length S RNA amplification may facilitate identification and molecular analysis of new arenaviruses or arenavirus strains