Structural insights into the substrate-bound condensation domains of non-ribosomal peptide synthetase AmbB.

Non-ribosomal peptide synthetases (NRPS) are multi-modular/domain enzymes that catalyze the synthesis of bioactive peptides. A crucial step in the process is peptide elongation accomplished by the condensation (C) domain with the aid of a peptidyl carrier or thiolation (T) domain. Here, we examined condensation reaction carried out by NRPS AmbB involved in biosynthesis of L-2-amino-4-methoxy-trans-3-butenoic acid (AMB) in P. aeruginosa. We determined crystal structures of the truncated T-C bidomain of AmbB in three forms, the apo enzyme with disordered T domain, the holo form with serine linked phosphopantetheine (Ppant) and a holo form with substrate (L-alanine) loaded onto Ppant. The two holo forms feature the T domain in a substrate-donation conformation. Mutagenesis combined with functional assays identified residues essential for the attachment of Ppant, anchoring the Ppant-L-Ala in the donor catalytic channel and the role of the conserved His953 in condensation activity. Altogether, these results provide structural insights into the condensation reaction at the donor site with a substrate-bound C domain of AmbB and lay the foundation for understanding the molecular mechanism of condensation which is crucial for AMB synthesis.

Pharmacokinetic interactions of drugs with St John's wort.

There is a worldwide increasing use of herbs which are often administered in combination with therapeutic drugs, raising the potential for herb-drug interactions. St John's wort (Hypericum perforatum) is one of the most commonly used herbal antidepressants. A literature search was performed using Medline (via Pubmed), Biological Abstracts, Cochrane Library, AMED, PsycINFO and Embase (all from their inception to September 2003) to identify known drug interaction with St John's wort. The available data indicate that St John's wort is a potent inducer of CYP 3A4 and P-glycoprotein (PgP), although it may inhibit or induce other CYPs, depending on the dose, route and duration of administration. Data from human studies and case reports indicate that St John's wort decreased the blood concentrations of amitriptyline, cyclosporine, digoxin, fexofenadine, indinavir, methadone, midazolam, nevirapine, phenprocoumon, simvastatin, tacrolimus, theophylline and warfarin, whereas it did not alter the pharmacokinetics of carbamazepine, dextromethorphan, mycophenolic acid and pravastatin. St John's wort decreased the plasma concentration of the active metabolite SN-38 in cancer patients receiving irinotecan treatment. St John's wort did not alter the pharmacokinetics of tolbutamide, but increased the incidence of hypoglycaemia. Several cases have been reported that St John's wort decreased cyclosporine blood concentration leading to organ rejection. St John's wort caused breakthrough bleeding and unplanned pregnancies when used concomitantly with oral contraceptives. It also caused serotonin syndrome when coadministered with selective serotonin-reuptake inhibitors (e.g. sertaline and paroxetine). Both pharmacokinetic and pharmacodynamic components may play a role in these interactions. Because the potential interaction of St John's wort with other drugs is a major safety concern, additional systematic research on herb-drug interactions and appropriate regulation in herbal safety and efficacy is needed.

Diversity and biochemical features of culturable fungi from the coastal waters of Southern China.

Fungi play a major role in various biogeochemical cycles of terrestrial and marine ecosystems. However, fungi in marine environments remain to be one of the most under-studied microbial groups. This study investigates the diversity of planktonic fungi from the coastal habitat off Pearl River Delta (China) using culture-dependent approach. A total of 22 fungi and 9 yeast isolates were recovered from 30 seawater and 2 sediment samples. Microscopic and ITS rRNA gene sequence analyses revealed that most of the fungi belonged to the phylum Ascomycota and Basidiomycota with a very small percentage (3%) of the subphylum Mucoromycotina of the Phylum Zygomycota. Most of these fungal isolates exhibited considerable production of extracellular enzymes, cellulase, lipase and laccase. Fungal isolates of two genera Mucor and Aspergillus sp. demonstrated pelletization capability over a wide range of pH, suggesting them as potential agents towards algae harvesting and wastewater treatment.