Search

The β-barrel assembly machine (BAM) mediates folding and insertion of integral β-barrel outer membrane proteins (OMPs) in Gram-negative bacteria. Of the five BAM subunits, only BamA and BamD are essential for cell viability. Here we present the crystal structure of a fusion between BamA POTRA4-5 and BamD from Rhodothermus marinus. The POTRA5 domain binds BamD between its tetratricopeptide repeats 3 and 4. The interface structural elements are conserved in the Escherichia coli proteins, which allowed structure validation by mutagenesis and disulfide crosslinking in E. coli. Furthermore, the interface is consistent with previously reported mutations that impair BamA-BamD binding. The structure serves as a linchpin to generate a BAM model where POTRA domains and BamD form an elongated periplasmic ring adjacent to the membrane with a central cavity approximately 30 × 60 Å wide. We propose that nascent OMPs bind this periplasmic ring prior to insertion and folding by BAM., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

This study reports a scalable and economical method to open a band gap in single layer graphene by deposition of cobalt metal on its surface using physical vapor deposition in high vacuum. At low cobalt thickness, clusters form at impurity sites on the graphene without etching or damaging the graphene. When exposed to oxygen at room temperature, oxygen functional groups form in proportion to the cobalt thickness that modify the graphene band structure. Cobalt/Graphene resulting from this treatment can support a band gap of 0.30 eV, while remaining largely undamaged to preserve its structural and electrical properties. A mechanism of cobalt-mediated band opening is proposed as a two-step process starting with charge transfer from metal to graphene, followed by formation of oxides where cobalt has been deposited. Contributions from the formation of both CoO and oxygen functional groups on graphene affect the electronic structure to open a band gap. This study demonstrates that cobalt-mediated oxidation is a viable method to introduce a band gap into graphene at room temperature that could be applicable in electronics applications.

Purpose: Parathyroid hormone (PTH), the only drug known to stimulate bone formation. is a peptide therapeutic indicated in the treatment of osteoporosis. Unfortunately, PTH is only effective when dosed by injection because it has no oral bioavailability. Herein we report the oral absorption of PTH in rats and monkeys facilitated by the novel delivery agent, N-[8-(2-hydroxy-4-methoxy)bensoyl]amino caprylic acid (4-MOAC)., Methods: 4-MOAC was selected from a group of 100 delivery agents based on in vitro chromotography studies and in vivo screening studies in rats. The PTH/4-MOAC combination was then tested in monkeys. The interaction of 4-MOAC and PTH was evaluated by nuclear magnetic resonance (NMR) spectroscopy., Results: Monkeys were administered an aqueous solution containing 4-MOAC and PTH and mean peak serum PTH concentrations of about 3000 pg/mL were obtained. The relative bioavailability of oral PTH was 2.1% relative to subcutaneous administration. The biological activity of the orally-delivered PTH was further evaluated in a rat model of osteoporosis. These studies showed that the bone formed following oral PTH/4-MOAC administration was comparable to that formed following PTH injections. The 4-MOAC mediated absorption of PTH is hypothesized to be the result of a noncovalent interaction between 4-MOAC and PTH. The preliminary evaluation of this interaction by NMR is described., Conclusions: 4-MOAC facilitates the absorption of PTH following oral administration to both rats and monkeys. The orally-absorbed PTH is biologically active as demonstrated in a rat model of osteoporosis.

Glucocorticoids inhibit the proliferation, but induce the differentiation, of bone marrow stromal cells into osteoblast-like cells. The mechanisms, however, are still conjectural. Since insulin-like growth factors (IGFs) have profound effects on osteoblast growth and differentiation, it is possible that glucocorticoids exert their effects on bone marrow stromal cells in part via regulation of IGFs. Therefore, we analyzed the effects of dexamethasone (Dex) on the expression of IGF I and IGF II in cultured preosteoblastic normal human bone marrow stromal cells (HBMSC). Whereas Dex decreased the concentration of IGF I in the conditioned medium since early in the treatment, the concentration of IGF II was increased progressively as culture period lengthened. As the activities of IGF I and IGF II are regulated by the IGF binding proteins (IGFBPs), we analyzed the effects of Dex on the expression of IGFBPs. Dex increased IGFBP-2 in a time-dependent manner. The increase in IGFBP-2, however, was only to the same extent as that of IGF II at most, depending on the length of treatment. Therefore, the increase in IGFBP-2 would dampen, but not eliminate, the increased IGF II activities. By contrast, Dex decreased IGFBP-3 levels, the latter increasing the bioavailability of IGF II. Although IGFBP-4 mRNA levels were stimulated by Dex, IGFBP-4 concentration in the conditioned medium was unchanged as measured by RIA. IGFBP-5 and IGFBP-6 mRNA levels were decreased by Dex in a time-dependent fashion. IGFBP-5 protein level was also decreased 1-4 days after Dex treatment. IGFBP-1 mRNA was not detectable in HBMSC. These accumulated data indicate that Dex regulates IGF I and IGF II and their binding proteins differentially in normal human bone marrow stromal cells. The progressive increase in IGF II may contribute to Dex-induced cell differentiation.

Osteoporosis, the result of an imbalance between bone resorption and bone formation, is a potential problem for the individual with a spinal cord injury because of the immobility commonly associated with this impairment. This study was performed to determine the diagnostic value of a new assay for urinary Pyridinium crosslink (UPyr). Assays were performed on 62 first morning voided and 50 24-hour urine specimens from clients in a bone health clinic. Higher than normal levels of UPyr were observed in females with osteoporosis. UPyr correlated well with urinary hydroxyproline (r = 0.429, p = 0.005; conversely, there was an inverse relationship between bone density and UPyr (r = -0.489, p = 0.01), positive correlation (r = 0.43, p = 0.011) between the 24-hour UPyr and a serum marker of bone resorption. The study confirms that UPyr has the ability to identify states of high bone resorption. This assay should be a welcome addition to the bone health assessment of individuals with risk factors such as impaired physical mobility.

Nuclear magnetic resonance assignments are reported at pH approximately 3 for a type 1 ("blue") copper protein, rusticyanin, obtained from the acidophilic organism Thiobacillus ferrooxidans. A combination of homonuclear proton and heteronuclear 15N-edited NMR spectra has been used to assign most of the 1H and 15N resonances of reduced rusticyanin. The copper-binding site is shown by analogy with other blue copper proteins to contain the side-chains of Cys138, His143 and Met148 at the C-terminal end of the sequence and a fourth ligand that is most likely a histidine, His85, consistent with the constitution of other type 1 copper sites. The global fold of the molecule is a compact beta-barrel or beta-sandwich, which contains a high proportion of beta-sheet secondary structure and a hydrophobic core particularly rich in aromatic residues. The copper-binding active site is surrounded by aromatic residues, and many of the resonances of the residues flanking the active site are shifted to unusual values, consistent with the effects of ring currents. The protected nature of the copper site is demonstrated by the large number of amide protons that are persistent in this region in 99% 2H2O solution at pH 3.4. We suggest that the unusual acid stability, both of the protein itself and of the blue copper active site, is a direct result of the protected and highly hydrophobic nature of the active site sequence and contacting loops and the high proportion of secondary structure in the protein.

A new member of the aurodox family of antibiotics, A83016F, has been isolated from an unidentified actionmycete designated A83016. The structure and relative stereochemistry of A83016F were elucidated by NMR examination of the parent compound and its diacetate derivative. A83016F exhibits only weak antimicrobial activity.

Actaplanin (A4696), a new complex of broad spectrum Gram-positive antibiotics is produced by Actinoplanes missouriensis. High performance liquid chromatography was used to show that this complex is composed of several actaplanins. Hydrolytic experiments with acetaplanins A, B1, B2, B3, C1 and G showed that these actaplanins were composed of the same peptide core, an amino sugar and varying amounts of glucose, mannose and rhamnose. The neutral sugar content was determined for each actaplanin. A bioautographic study of aglycone formation during hydrolysis of the actaplanin complex showed that within a short time a simple mixture of two antimicrobially active hydrolysis products was obtained. These substances retained the antimicrobial spectrum and a high percentage of the antibiotic activity of the parent actaplanin complex. Methanolysis of the acetaplanin complex as well as the individual actaplanins resulted in the selective loss of the neutral sugar moieties and the isolation of actaplanin psi (pseudo)-aglycone--the core peptide which still retained an amino sugar group. The 1H NMR spectrum of this substance indicated a similarity to many features of ristocetin psi-aglycone. Hydrolytic studies showed that the amino sugar present in actaplanin was identical with L-ristosamine. It is concluded that the aglycone of actaplanin is a complex peptide composed of aromatic amino acids, and that the actaplanins each possess this aglycone and L-ristosamine but are differentiated by their neutral sugar composition.

A37812, a new member of the streptothricin class of antibiotics, has been isolated and characterized as N-methylstreptothricin F. The structure elucidation of A37812 is based on results from 13C and 1H NMR spectroscopies.

This article presents the fundamental knowledge nurse practitioners need when managing the care of a client with mitral valve prolapse (MVP). The assessment discussion includes information on where and how to perform cardiac auscultation, and it also includes a discussion of the particular mid-to-late systolic click with murmur that is typical of MVP. Client preparation for diagnostic tests (echocardiogram and ECG) is also presented. Potential complications of endocarditis, mitral regurgitation, ventricular dysrhythmia, chest pain, systemic emboli and sudden death are discussed. Particular emphasis is given to the nursing management and client teaching that are required for clients with MVP. Nursing management includes teaching the client 1) the need and schedule for chemoprophylaxis of endocarditis, 2) how to maintain left ventricular volume, 3) the possible relationship between chest pain and hypovolemia and 4) the advantages of regular exercise. Changes in the click-murmur that may occur with pregnancy and the impact of MVP on contraception and childbearing decisions are discussed. Specific nursing diagnoses that may arise with the client with MVP are listed. Outcome criteria that may be used for evaluation of nursing care are provided.

Multilayered liposome (MLV) formation from water/organic-solvent (W/O) emulsions was studied. A fundamental liposome population parameter, the E(ratio), was defined and used to estimate the bilayer number and water spacing in MLV liposomes. MLVs prepared from W/O emulsions have optimum drug entrapment at an emulsion-lipid/emulsion-water ratio of ∼0.33. Drug entrapment is typically 50 to 65% under these optimal conditions.

The antifungal antibiotic, echinocandin B (ECB), was modified by a sequential procedure in which the initial step involved enzymatic removal of the native N-linoleoyl group from the N-terminus using an Actinoplanes utahensis culture. The resulting product, ECB nucleus, was reacylated using active esters or acid halides of various substituted acids to give a series of ECB analogs. These analogs possessed anti-Candida activity both in vitro and in vivo (mice). Other studies have shown that one of these, cilofungin, the 4-n-octyloxybenzoyl-ECB analog (LY121019), has excellent anti-Candida activity, low toxicity and is superior to other available antifungal antibiotics.

A58365A and A58365B, angiotensin converting enzyme inhibitors isolated from the culture filtrate of Streptomyces chromofuscus NRRL 15098, are homologous compounds of molecular formulas C12H13NO6 and C13H15NO6. The molecular similarities of the two inhibitors were established by comparison of their 1H NMR, 13C NMR, and UV spectra. Catalytic hydrogenation of A58365A led to a tetrahydro-deoxy derivative, C12H17NO5; extensive 1H NMR decoupling studies at 360 MHz allowed all the non-exchangeable protons of the derivative to be connected in a continuous substructure. This fragment was combined with information from other spectroscopic methods to suggest the structures for A58365A (1) and A58365B (2); the conclusions were confirmed by an X-ray crystallographic analysis of A58365A-dimethyl ester.

The use of digital subtraction angiography (DSA) is increasing. Nurses must be prepared to provide quality care to patients who have this relatively new method for radiographically studying the blood vessels. A description of DSA and its applications is provided. Patient preparation, assessment, teaching, and management are described. Complications of the procedure and their management are presented.

A culture identified as Streptomyces karnatakensis was found to produce a novel cyclic hexadepsipeptide antibiotic designated A83586C. The structure was elucidated by X-ray crystallography, and full 1H and 13C NMR assignments are reported. The absolute configuration was confirmed by the detection of D-threonine in the acid hydrolysate of A83586C. A83586C had potent Gram-positive activity in vitro but lacked in vivo efficacy in mice.

The novel lipopeptide antibiotic A21978C complex is active against Gram-positive organisms. This complex consists of a common peptide nucleus with various lipid acyl groups at the N-terminus characteristic of each individual factor. The fatty acid acyl group is removed by incubation of the A21978C complex with Actinoplanes utahensis to give the peptide nucleus. This peptide nucleus has the same amino acid sequence as A21978C. New analogs of A21978C were synthesized by acylation of the N-terminus of a tert-butoxycarbonyl (tert-BOC)-protected nucleus and subsequent deprotection. 1H NMR showed that the newly introduced acyl group was at the desired N-terminus. Three major groups of analogs were synthesized bearing fatty acid acyl, amino-aroyl and extended peptide side chains. Each analog was evaluated for antimicrobial activity and acute toxicity. Of these analogs, the n-decanoyl analog of A21978C (LY146032) gave the best survival in the mouse acute toxicity test at a high dose of 1,000 mg/kg, iv and was chosen for further study. This analog has been named daptomycin.