Analysis of the gene cluster from Streptomyces avermitilis that governs the biosynthesis of the polyketide anthelmintic avermectin revealed that it contains four large ORFs encoding giant multifunctional polypeptides of the avermectin polyketide synthase (AVES 1, AVES 2, AVES 3, and AVES 4). These clustered polyketide synthase genes responsible for avermectin biosynthesis together encode 12 homologous sets of enzyme activities (modules), each catalyzing a specific round of polyketide chain elongation. The clustered genes encoding polyketide synthase are organized as two sets of six modular repeats, aveA1-aveA2 and aveA3-aveA4, which are convergently transcribed. The total of 55 constituent active sites makes this the most complex multifunctional enzyme system identified to date. The sequenced DNA region contains 14 additional ORFs, some of which encode polypeptides governing other key steps in avermectin biosynthesis. Between the two sets of polyketide synthase genes lie two genes involved in postpolyketide modification, one of which encodes cynthochrome P450 hydroxylase that probably catalyzes furan ring formation at C6 to C8a. Immediately right of the large polyketide synthase genes is a set of genes involved in oleandrose biosynthesis and its transglycosylation to polyketidederived aglycons. This cluster includes nine genes, but one is not functional in the biosynthesis of avermectin. On the left side of polyketide synthase genes, two ORFs encoding methyltransferase and nonpolyketide synthase ketoreductase involved in postpolyketide modification are located to the left of the polyketide synthase genes, and an adjacent gene encodes a regulatory function that may be involved in activation of the transcription of avermectin biosynthetic genes.Streptomyces avermitilis produces avermectin, a series of eight related pentacyclic lactones that contain a disaccharide of the methylated deoxysugar oleandrose (1). Avermectin and the related compounds milbemycin and nemadectin are potent anthelmintic compounds, the former two of which are used commercially in animal healthcare and agriculture. The semisynthetic derivatives of avermectin C22, C23 dihydroavermectin B1, ivermectin, are widely used for the treatment of diseases caused by nematodes and arthropods in veterinary and agricultural fields, respectively. Ivermectin has been used for livestock farming and health care of companion animals.

We have cloned a gene (aphA) encoding acetylpolyamine amidohydrolase from Mycoplana ramosa ATCC 49678 (previously named Mycoplana bullata). A genomic library of M. ramosa was screened with an oligonucleotide probe designed from a N-terminal amino acid sequence of the enzyme purified from M. ramosa. Nucleotide sequence analysis revealed an open reading frame of 1,023 bp which encodes a polypeptide with a molecular mass of 36,337 Da. This is the first report of the structure of acetylpolyamine amidohydrolase. The aphA gene was subcloned under the control of the trc promoter and was expressed in Escherichia coli MM294. The recombinant enzyme was purified, and the enzymatic properties were characterized. Substrate specificities, K m values, and V max values were identical to those of the native enzyme purified from M. ramosa. In the analysis of the metal-substituted enzymes, we found that the acid limb of pH rate profiles shifts from 7.2 for the original zinc enzyme to 6.6 for the cobalt enzyme. This change suggests that the zinc atom is essential for the catalytic activity of the enzyme similarly to the zinc atom in carboxypeptidase A.Polyamines (putrescine, cadaverine, spermidine, and spermine) are bioactive amines widely distributed among both eukaryotic and prokaryotic cells. Polyamines and their metabolites are essential for normal cell growth, although details of their functions have not been fully elucidated (22). In higher eukaryotes, polyamines modulate channel activities of N-methyl-D-aspartate receptors, which play an important role in glutamate-mediated neuronal plasticity and neurotoxicity in the central nervous system (17). Spermine also functions to stimulate the protein kinase casein kinase 2 (12).Biosynthetic pathways for polyamines are well established (14,22). Four key enzymes make up the pathway of polyamine synthesis. L-Ornithine decarboxylase forms putrescine from Lornithine. S-Adenosylmethionine decarboxylase forms decarboxylated S-adenosylmethionine, which acts as an aminopropyl donor. Spermidine synthase and spermine synthase transfer the aminopropyl group from decarboxylated S-adenosylmethionine to putrescine and spermidine, respectively. Specific inhibitors of these enzymes are now available and are used as therapeutic agents for African sleeping sickness and cancer.In eukaryotic cells, the retroconversion of spermine to putrescine can be accomplished by sequential actions of spermidine-spermine N 1 -acetyltransferase and polyamine oxidase. In microorganisms, however, polyamine oxidase and acetylpolyamine amidohydrolase are involved in degradative pathways of acetylpolyamines (14). It is uncertain whether some types of acetylpolyamines are catabolized via deacetylation by acetylpolyamine amidohydrolases while the others are catabolized by polyamine oxidases. The acetylpolyamine amidohydrolases found in Streptomyces avellaneus (18), Arthrobacter sp. (10), and Micrococcus rubens (15) act only on acetylputrescine. A novel acetylpolyamine amidohydrolase which acts upon all types of acetylpolya...

Antibody-dependent cellular cytotoxicity (ADCC) is dependent on the fucose content of oligosaccharides bound to monoclonal antibodies (MAbs). As MAbs with a low fucose content exhibit high ADCC activity, it is important to control the defucosylation levels (deFuc%) of MAbs and to analyze the factors that affect deFuc%. In this study, we observed that the deFuc% was inversely related to culture medium osmolality for MAbs produced in the rat hybridoma cell line YB2/0, with r 2 values as high as 0.92. Moreover, deFuc% exhibited the same correlation irrespective of the type of compound used for regulating osmolality (NaCl, KCl, fucose, fructose, creatine, or mannitol) at a culture scale ranging from 1 to 400 L. We succeeded in controlling MAb deFuc% by maintaining a constant medium osmolality in both perfusion and fed-batch cultures. In agreement with these observations, reverse transcription PCR analyses revealed decreased transcription of genes involved in glycolysis, GDP-fucose supply, and fucose transfer under hypoosmotic conditions.

We have cloned the Micromonospora viridifaciens neuraminidase (EC 3.2.1.18) gene (nedA) in Streptomyces fividans. This was accomplished by using the vector pU7O2 and BgM-BclI libraries of M. viridifaciens chromosomal inserts created in S. fividans. The libraries were screened for the expression of neuraminidase by monitoring the cleavage of the fluorogenic neuraminidase substrate 2'-(4-methylumbelliferyl)-a-D-N-acetylneuraminic acid. Positive clones (BG6, BG7, BC4, and BC8) contained the identical 2-kb BclI-BgI fragment and expressed neuraminidase efficiently and constitutively using its own promoter in the heterologous host. From the nucleotide sequence analysis, an open reading frame of 1,941 bp which encodes a polypeptide with an M, of 68,840 was detected. The deduced amino acid sequence has five Asp boxes, -Ser-X-Asp-X-Gly-XThr-Trp, showing great similarity to other bacterial and viral neuraminidases. We have also identified the catalytic domain by using truncated proteins produced in S. fividans. Neuraminidase (EC 3.2.1.18) is a glycosidase which cleaves an a-ketosidic linkage between sialic acid and the adjacent sugar residue on glycoproteins, glycolipids, and oligosaccharides. It is widely distributed in microorganisms such as viruses, bacteria, and actinomycetes and in various tissues from fowls and mammals. For myxovirus it is an important surface antigen and also plays a role in facilitating the movement of the virus both to and from the site of infection (1). Bacteria and actinomycetes which produce neuraminidase can release sialic acids from glycoconjugates for use as carbon and energy sources. In pathogenic microorganisms, neuraminidase activity has a strong correlation with pathogenesis (27).Recently, neuraminidase genes were cloned from several pathogenic microorganisms, including Clostridium sordellii G12 (25), Clostridium perfringens A99 (24), Salmonella typhimurium LT-2 (23), Vibrio cholerae 395 (29), and Bacteroides fragilis TAL2480 (26). From examination of their deduced amino acid sequences, a conserved sequence of 12 amino acids (Asp box) which was repeated at four or five positions was found (23). This conserved sequence shows similarity to the neuraminidase of influenza virus A H7N1 and H13N9. The structures of neuraminidases from nonpathogenic bacteria have not been characterized. In a recent report, neuraminidase was widely found in culture fluids of actinomycetes (3). For Micromonospora spp., 10 of the 39 strains examined exhibited neuraminidase activity. Micromonospora viridifaciens showed the highest neuraminidase activity among this group. Neuraminidase from M.viridifaciens was purified, and its properties were analyzed (2). Neuraminidase activity in M. viridifaciens was detected in the culture broth only when a substrate such as colominic acid or the product N-acetylneuraminic acid was present in the culture medium (2).We would like to understand the regulation of neuraminidase gene (ned4) expression and the properties of its * Corresponding author. product in M. viridifaciens and ...