An approach to the biosynthetic pathway of butirosins and the related antibiotics.
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Four 2-deoxystreptamine (DOS) related compounds including S-11-P, isolated as an intermediate of DOS biosynthesis, were supplemented to the culture of a DOS- mutant of Bacillus circulans. Among the tested aminocyclitol compounds, S-11-P alone was converted to DOS. Addition of other aminocyclitols neither produced antibiotic nor inhibited the incorporation of S-11-P and DOS into butirosins. By these facts, S-11-P was confirmed clearly to be an intermediate of DOS biosynthesis.
The catalytic properties of the partially purified deacetoxycephalosporin C (DAOC)-synthetase and DAOC-hydroxylase from an industrial strain of Cephalosporium acremonium were studied. After mechanical breakage of the cells, purification was achieved by fractional (NH4)2SO4 precipitation, gel chromatography on Sephadex G-75, ion exchange chromatography on DEAE-Trisacryl M and two isoelectric focusing steps. The two enzyme activities could not be separated. Indirect evidence was obtained from SDS-polyacrylamide gel electrophoresis of the purest fractions obtained by isoelectric focusing that the two reactions are catalyzed by a single enzyme with a molecular weight of 33,000 +/- 2,000 and a pI of 4.6 +/- 0.1. Both reactions require alpha-ketoglutarate, FeSO4, ascorbate and O2, whereas additional ATP shows only a slight stimulation.
The genes for most of the biosynthesis of the kinamycin antibiotics have been cloned and heterologously expressed. Genomic DNA of Streptomyces murayamaensis was partially digested with MboI and a library of approximately 40 kb fragments in E. coli XL1-BlueMR was prepared using the cosmid vector pOJ446. Hybridization with the actI probe from the actinorhodin polyketide synthase genes identified two clusters of polyketide genes. After transferal of these clusters to S. lividans ZX7, expression of one cluster was established by HPLC with photodiode array detection. Peaks were identified from the kin cluster for dehydrorabelomycin, kinobscurinone, and stealthin C, which are known intermediates in kinamycin biosynthesis. Two shunt metabolites, kinafluorenone and seongomycin were also identified. The structure of the latter was determined from a quantity obtained from large-scale fermentation of one of the clones.
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Starting from a super-repressed mutant of purR, 3-18, 439 independent candidates of purR- mutants were isolated by using NCE selecting plate with lactose as sole carbon source. Among these mutants. 11 amber mutants were detected by introducing a tRNA suppressor gene. Cotransduction analysis proved that the amber mutation sites of 11 amber mutants all located on purR. Amino acid substitution experiments were performed with three tRNA suppressors, supD, supE and supF, for each purR(am). The results showed that the same amino acid substitution occurred in different site of PurR protein could result in varied effects on purR function; different amino acid substitution occurred at the same position of PurR protein also could produced varied effects on purR function.
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The regulation of AMPA receptors at the postsynaptic membrane is a fundamental component of synaptic plasticity. In the hippocampus, the induction of long-term potentiation increases the delivery of GluR1, a major AMPA receptor subunit in hippocampal pyramidal neurons, to the synaptic plasma membrane through a mechanism that requires the PDZ binding domain of GluR1. Synapse-associated protein 97 (SAP97), a member of the membrane-associated guanylate kinase family, is believed to associate with AMPA receptors (AMPARs) containing the GluR1 subunit, but the functional significance of these interactions is unclear. We investigated the interaction of GluR1 with SAP97, the only PDZ protein known to interact with GluR1. We find that interactions involving SAP97 and GluR1 occur early in the secretory pathway, while the receptors are in the endoplasmic reticulum or cis-Golgi. In contrast, few synaptic receptors associate with SAP97, suggesting that SAP97 dissociates from the receptor complex at the plasma membrane. We also show that internalization of GluR1, as triggered by NMDAR activation, does not require SAP97. These results implicate GluR1-SAP97 interactions in mechanisms underlying AMPA receptor targeting.
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