Solution Structures of the Acyl Carrier Protein Domain from the Highly Reducing Type I Iterative Polyketide Synthase CalE8

Biosynthesis of the enediyne natural product calicheamicins γ1I in Micromonospora echinospora ssp. calichensis is initiated by the iterative polyketide synthase (PKS) CalE8. Recent studies showed that CalE8 produces highly conjugated polyenes as potential biosynthetic intermediates and thus belongs to a family of highly-reducing (HR) type I iterative PKSs. We have determined the NMR structure of the ACP domain (meACP) of CalE8, which represents the first structure of a HR type I iterative PKS ACP domain. Featured by a distinct hydrophobic patch and a glutamate-residue rich acidic patch, meACP adopts a twisted three-helix bundle structure rather than the canonical four-helix bundle structure. The so-called ‘recognition helix’ (α2) of meACP is less negatively charged than the typical type II ACPs. Although loop-2 exhibits greater conformational mobility than other regions of the protein with a missing short helix that can be observed in most ACPs, two bulky non-polar residues (Met992, Phe996) from loop-2 packed against the hydrophobic protein core seem to restrict large movement of the loop and impede the opening of the hydrophobic pocket for sequestering the acyl chains. NMR studies of the hydroxybutyryl- and octanoyl-meACP confirm that meACP is unable to sequester the hydrophobic chains in a well-defined central cavity. Instead, meACP seems to interact with the octanoyl tail through a distinct hydrophobic patch without involving large conformational change of loop-2. NMR titration study of the interaction between meACP and the cognate thioesterase partner CalE7 further suggests that their interaction is likely through the binding of CalE7 to the meACP-tethered polyene moiety rather than direct specific protein-protein interaction

Diversity of anopheline species and their <it>Plasmodium</it> infection status in rural Bandarban, Bangladesh

<p>Abstract</p> <p>Background</p> <p>Historically, the Chittagong Hill Tracts (CHT) of Bangladesh was considered hyperendemic for malaria. To better understand the contemporary malaria epidemiology and to develop new and innovative control strategies, comprehensive epidemiologic studies are ongoing in two endemic unions of Bandarban district of CHT. Within these studies entomological surveillance has been undertaken to study the role of the existing anopheline species involved in the malaria transmission cycle throughout the year.</p> <p>Methods</p> <p>CDC miniature light traps were deployed to collect anopheline mosquitoes from the sleeping room of the selected houses each month in a single union (Kuhalong). Molecular identification was carried out for available <it>Anopheles</it> species complexes. Circumsporozoite proteins (CSP) for <it>Plasmodium falciparum</it>, <it>Plasmodium vivax</it>-210 (Pv-210) and <it>Plasmodium vivax</it>-247(Pv-247) were detected by Enzyme-linked immunosorbent assay (ELISA) from the female anopheline mosquitoes. To confirm CSP-ELISA results, polymerase chain reaction (PCR) was also performed.</p> <p>Results</p> <p>A total of 2,837 anopheline mosquitoes, of which 2,576 were female, belonging to 20 species were collected from July 2009 -June 2010. <it>Anopheles jeyporiensis</it> was the most abundant species (18.9%), followed by <it>An. vagus</it> (16.8%) and <it>An. kochi</it> (14.4%). ELISA was performed on 2,467 female mosquitoes of 19 species. 15 (0.6%) female anophelines belonging to eight species were found to be positive for <it>Plasmodium</it> infection by CSP-ELISA. Of those, 11 (0.4%) mosquitoes were positive for <it>P. falciparum</it> and four (0.2%) for Pv-210. No mosquito was found positive for Pv-247. <it>An. maculatus</it> (2.1%, 2/97) had the highest infection rate followed by <it>An. umbrosus</it> (1.7%, 2/115) and <it>An. barbirostris</it> (1.1%, 2/186). Other infected species were <it>An. nigerrimus</it>, <it>An. nivipes, An. jeyporiensis</it>, <it>An. kochi</it>, and <it>An. vagus</it>. Out of 11 <it>P. falciparum</it> CSP positive samples, seven turned out to be positive by PCR. None of the samples positive for Pv-210 was positive by PCR. In terms of abundance and incrimination, the results suggest that <it>An. maculatus</it>, <it>An. jeyporiensis</it> and <it>An. nivipes</it> play important roles in malaria transmission in Kuhalong.</p> <p>Conclusion</p> <p>The findings of this study suggest that even in the presence of an insecticide impregnated bed-net intervention, a number of <it>Anopheles</it> species still play a role in the transmission of malaria. Further investigations are required to reveal the detailed biology and insecticide resistance patterns of the vector mosquito species in endemic areas in Bangladesh in order to assist with the planning and implementation of improved malaria control strategies.</p