Intracolonial allocation of trisoxazole macrolides in the sponge Pachastrissa nux

Pachastrissa nux has two distinctive growth forms in one colony, i.e., the protruding gorgonian-shaped capitum and the substratum-attached irregular-shaped base. The sponge has the ability to allocate specifically its major secondary metabolites to the two parts in different levels. Using two cytotoxic trisoxazole macrolides, kabiramides C (2) and G (3), as chemical markers, it was found that the capitum accumulated higher contents of either or both compounds than did the base. However, there were neither inductive nor suppressive correlations among the allocation profiles of either compound in either part of the sponge. The allocation of kabiramides was a trade-off with the structural materials involved in reinforcing the strength of the sponge. To date, this is the second report that provides evidence of the specific allocation of bioactive metabolites in two distinctively different organ-like structures in a single sponge colony.     

Antimicrobial susceptibilities of Propionibacterium acnes isolated from patients with acne vulgaris

Antibiotic susceptibilities of Propionibacterium acnes in Japan were determined. Erythromycin‐resistance was found in 10.4% (5/48) of the strains, and four of these were cross‐resistance to clindamycin. Although the erythromycin ribosome methylase gene erm(X) was looked for, no strain carrying erm(X) was found. Sequencing analysis revealed that all of the erythromycin‐resistant strains had a mutation in the peptidyl transferase region of the 23S rRNA gene: G2057A, A2058G, or A2059G. Consequently, our results show that P. acnes resistance to macrolides is caused by a mutation in the 23S rRNA gene, and has been increasing in Japan.     

使用微丝骨架解聚剂对橡胶树进行刺激采胶的研究

初步研究了不同浓度的(1%,5%,10%)KI、饱和浓度的大环内酯作为微丝骨架解聚剂对橡胶树的刺激排胶效果.2%的甲基纤维素处理的橡胶树作为空白.测定了各处理橡胶树的胶乳产量及胶乳的6种生理参数,即干胶含量、总固形物含量、蔗糖含量、无机磷含量、硫醇含量以及镁离子含量.结果表明施用1%KI和饱和浓度大环内酯的橡胶树胶乳产量大量增加,其增产幅度与作为天然橡胶常用刺激采胶剂--0.3%的乙烯利的增产幅度大致相当.比较通过1%KI和饱和浓度大环内酯刺激采胶的胶乳和0.3%的乙烯利刺激采胶的胶乳的各生理参数发现,3种处理得来的胶乳干胶含量和总固形物含量并没有明显的差别,但各处理的其它4个生理参数却差别明显,这意味着KI和饱和浓度大环内酯使橡胶树胶乳增产机制可能与乙烯利的机制不同.值得一提的是,高浓度的KI对橡胶树有明显的副作用,长时间的使用会引起橡胶树死皮病的发生.     

Ribosome protection by ABC‐F proteins—Molecular mechanism and potential drug design

Members of the ATP‐binding cassette F (ABC‐F) proteins confer resistance to several classes of clinically important antibiotics through ribosome protection. Recent structures of two ABC‐F proteins, Pseudomonas aeruginosa MsrE and Bacillus subtilis VmlR bound to ribosome have shed light onto the ribosome protection mechanism whereby drug resistance is mediated by the antibiotic resistance domain (ARD) connecting the two ATP binding domains. ARD of the E site bound MsrE and VmlR extends toward the drug binding region within the peptidyl transferase center (PTC) and leads to conformational changes in the P site tRNA acceptor stem, the PTC, and the drug binding site causing the release of corresponding drugs. The structural similarities and differences of the MsrE and VmlR structures likely highlight an universal ribosome protection mechanism employed by antibiotic resistance (ARE) ABC‐F proteins. The variable ARD domains enable this family of proteins to adapt the protection mechanism for several classes of ribosome‐targeting drugs. ARE ABC‐F genes have been found in numerous pathogen genomes and multi‐drug resistance conferring plasmids. Collectively they mediate resistance to a broader range of antimicrobial agents than any other group of resistance proteins and play a major role in clinically significant drug resistance in pathogenic bacteria. Here, we review the recent structural and biochemical findings on these emerging resistance proteins, offering an update of the molecular basis and implications for overcoming ABC‐F conferred drug resistance.     

The structural basis of macrolide-ribosome binding assessed using mutagenesis of 23S rRNA positions 2058 and 2059

Macrolides are a diverse group of antibiotics that inhibit bacterial growth by binding within the peptide tunnel of the 50S ribosomal subunit. There is good agreement about the architecture of the macrolide site from different crystallography studies of bacterial and archaeal 50S subunits. These structures show plainly that 23S rRNA nucleotides A2058 and A2059 are located accessibly on the surface of the tunnel wall where they act as key contact sites for macrolide binding. However, the molecular details of how macrolides fit into this site remain a matter of contention. Here, we have generated an isogenic set of single and dual substitutions at A2058 and A2059 in Mycobacterium smegmatis to investigate the effects of the rRNA mutations on macrolide binding. Resistances conferred to a comprehensive array of 11 macrolide compounds are used to assess models of macrolide binding predicted from the crystal structures. The data indicate that all macrolides and their derivatives bind at the same site in the tunnel with their C5 amino sugar in a similar orientation. Our data are compatible with the lactone rings of 14-membered and 16-membered macrolides adopting different conformations, enabling the latter compounds to avoid a steric clash with 2058G. This difference, together with interactions conveyed via substituents that are specific to certain ketolide and macrolide sub-classes, influences the binding to the large ribosomal subunit. Our genetic data show no support for a derivatized-macrolide binding site that has been proposed to be located further down the tunnel.     

Effect of nitrogen source on biosynthesis of rapamycin by Streptomyces hygroscopicus

Six non-amino acid nitrogen compounds were examined as nitrogen source for growth of Streptomyces hygroscopicus and biosynthesis of rapamycin. Of the nitrogen sources studied, ammonium sulfate was the best with respect to formation of rapamycin, and supported cell growth comparable to the organic nitrogen sources used in the control chemically defined medium, ie, aspartate, arginine plus histidine. In the new chemically defined medium, which is buffered with 200 mM 2-(N-morpholino)ethanesulfonic acid to prevent decline of pH during fermentation, an ammonium sulfate concentration of 40 mM was optimal for biosynthesis of rapamycin. Rapamycin production increased by more than 30% on both volumetric and specific bases as compared to the previous medium containing the three amino acids as nitrogen source. Received 08 November 1996/ Accepted in revised form 07 April 1997     

Peptide derivatives of tylosin-related macrolides

Approaches to the synthesis of model compounds based on the tylosin-related macrolides desmycosin and O=mycaminosyltylonolide were developed to study the conformation and topography of the nascent peptide chain in the ribosome tunnel using specially designed peptide derivatives of macrolide antibiotics. A method for selective bromoacetylation of desmycosin at the hydroxyl group of mycinose was developed, which involves preliminary acetylation of mycaminose. The reaction of the 4″-bromoacetyl derivative of the antibiotic with cesium salts of the dipeptide Boc-Ala-Ala-OH and the hexapeptide MeOTr-Gly-Pro-Gly-Pro-Gly-Pro-OH led to the corresponding peptide derivatives of desmycosin. The protected peptides Boc-Ala-Ala-OH, Boc-Ala-Ala-Phe-OH, and Boc-Gly-Pro-Gly-Pro-Gly-Pro-OH were condensed with the C23-hydroxyl group of O-mycaminosyltylonolide.     

Azithromycin, a lysosomotropic antibiotic, impairs fluid-phase pinocytosis in cultured fibroblasts

The dicationic macrolide antibiotic azithromycin inhibits the uptake of horseradish peroxidase (HRP) by fluid-phase pinocytosis in fibroblasts in a time- and concentration-dependent fashion without affecting its decay (regurgitation and/or degradation). The azithromycin effect is additive to that of nocodazole, known to impair endocytic uptake and transport of solutes along the endocytic pathway. Cytochemistry (light and electron microscopy) shows a major reduction by azithromycin in the number of HRP-labeled endocytic vesicles at 5 min (endosomes) and 2 h (lysosomes). Within 3 h of exposure, azithromycin also causes the appearance of large and light-lucentlelectron-lucent vacuoles, most of which can be labeled by lucifer yellow when this tracer is added to culture prior to azithromycin exposure. Three days of treatment with azithromycin result in the accumulation of very large vesicles filled with pleiomorphic content, consistent with phospholipidosis. These vesicles are accessible to fluorescein-labeled bovine serum albumin (FITC-BSA) and intensively stained with filipin, indicating a mixed storage with cholesterol. The impairment of HRP pinocytosis directly correlates with the amount of azithromycin accumulated by the cells, but not with the phospholipidosis induced by the drug. The proton ionophore monensin, which completely suppresses azithromycin accumulation, also prevents inhibition of HRP uptake. Erythromycylamine, another dicationic macrolide, also inhibits HRP pinocytosis in direct correlation with its cellular accumulation and is as potent as azithromycin at equimolar cellular concentrations. We suggest that dicationic macrolides inhibit fluid-phase pinocytosis by impairing the formation of pinocytic vacuoles and endosomes.     

Spongia属沐浴海绵化学成分及生理活性研究概况

已进行化学成分研究的Spongia属沐浴海绵有15个种,主要化学成分有大环内酯,萜类,甾醇,神经酰胺和一些长链脂肪酸,脂等,其中一些化学成分具有结构新颖性和较好的生理活性,综述了国内外有关该属沐浴海绵化学成分及生理活性的研究概况。