CHO DUKX cell lineages preadapted to growth in serum-free suspension culture enable rapid development of cell culture processes for the manufacture of recombinant proteins

Using an adaptive strategy, Chinese hamster ovary (CHO) cell lines were developed that are capable of robust growth in serum-free suspension culture. These preadapted derivatives of the commonly used strain of CHO cells (CHO DUKX), termed PA-DUKX, were used for the introduction and stable expression of several heterologous human genes. A significant advantage of recombinant PA-DUKX cells was their ability to readily resume growth in serum-free suspension culture after transfection and amplification of heterologous genes. Expression of recombinant human proteins in PA-DUKX cells was quantitatively similar to that of lineages generated using conventional CHO DUKX cells. In addition, recombinant human proteins expressed by transfected PA-DUKX lineages were shown to be biochemically and structurally similar to those expressed in CHO DUKX cells, PA-DUKX host cell technology provides an opportunity for reducing the time and resources required to develop large-scale, suspension culture-based manufacturing processes employing serum-free medium. (c) 1996 John Wiley & Sons, Inc.     

Shakers and head bangers: differences in sonication behavior between Australian <Emphasis Type="Italic">Amegilla murrayensis</Emphasis> (blue-banded bees) and North American <Emphasis Type="Italic">Bombus impatiens</Emphasis> (bumblebees)

Many bees collect pollen by grasping the anthers of a flower and vibrating their flight muscles at high frequencies—a behavior termed sonication, or buzz-pollination. Here we compare buzz-pollination on Solanum lycopersicum (cherry tomatoes) by two bees that fill similar niches on different continents—in Australia, Amegilla murrayensis (blue-banded bee), and in North America, Bombus impatiens (bumblebee). We collected audio recordings of buzz-pollination and quantified the frequency and length of buzzes, as well as the total time spent per flower. We found that A. murrayensis buzzes at significantly higher frequencies (~350 Hz) than B. impatiens (~240 Hz) and flaps its wings at higher frequencies during flight. There was no difference in the length of a single buzz, but A. murrayensis spent less time on each flower, as B. impatiens buzzed the flower several times before departing, whereas A. murrayensis typically buzzed the flower only once. High-speed videos of A. murrayensis during buzz-pollination revealed that its physical interaction with the flower differs markedly from the mechanism described for Bombus and other bees previously examined. Rather than grasping the anther cone with its mandibles and shaking, A. murrayensis taps the anther cone with its head at the high buzzing frequencies generated by its flight muscles. This unique behavior, combined with its higher buzzing frequency and reduced flower visit duration, suggests that A. murrayensis may be able to extract pollen more quickly than B. impatiens, and points to the need for further studies directly comparing the pollination effectiveness of these species.     

Cloning of the Bacillus subtilis glutamine phosphoribosylpyrophosphate amidotransferase gene in Escherichia coli. Nucleotide sequence determination and properties of the plasmid-encoded enzyme

The Bacillus subtilis gene encoding glutamine phosphoribosylpyrophosphate amidotransferase (amidophosphoribosyltransferase) was cloned in pBR322. This gene is designated purF by analogy with the corresponding gene in Escherichia coli. B. subtilis purF was expressed in E. coli from a plasmid promoter. The plasmid-encoded enzyme was functional in vivo and complemented an E. coli purF mutant strain. The nucleotide sequence of a 1651-base pair B. subtilis DNA fragment was determined, thus localizing the 1428-base pair structural gene. A primary translation product of 476 amino acid residues was deduced from the DNA sequence. Comparison with the previously determined NH2-terminal amino acid sequence indicates that 11 residues are proteolytically removed from the NH2 terminus, leaving a protein chain of 465 residues having an NH2-terminal active site cysteine residue. Plasmid-encoded B. subtilis amidophosphoribosyltransferase was purified from E. coli cells and compared to the enzymes from B. subtilis and E. coli. The plasmid-encoded enzyme was similar in properties to amidophosphoribosyltransferase obtained from B. subtilis. Enzyme specific activity, immunological reactivity, in vitro lability to O2, Fe-S content, and NH2-terminal processing were virtually identical with amidophosphoribosyltransferase purified from B. subtilis. Thus E. coli correctly processed the NH2 terminus and assembled [4Fe-4S] centers in B. subtilis amidophosphoribosyltransferase although it does not perform these maturation steps on its own enzyme. Amino acid sequence comparison indicates that the B. subtilis and E. coli enzymes are homologous. Catalytic and regulatory domains were tentatively identified based on comparison with E. coli amidophosphoribosyltransferase and other phosphoribosyltransferase (Argos, P., Hanei, M., Wilson, J., and Kelley, W. (1983) J. Biol. Chem. 258, 6450-6457).     

Oxygen-18 studies of the mechanism of pyrophosphoryl group transfer catalyzed by phosphoribosylpyrophosphate synthetase.

The formation of phosphoribosylpyrophosphate (PRPP) and adenosine 5′-monophosphate (AMP) from ribose 5-phosphate and adenosine 5′-triphosphate, catalyzed by purified PRPP synthetase from Salmonella typhimurium, was conducted in ¹⁸O-enriched water. The products were isolated, and inorganic phosphate was isolated from AMP and the pyrophosphoryl moiety of PRPP. Oxygen-18 was incorporated into PRPP but not into AMP. These results indicate that PRPP synthesis proceeds with scission of a βPO bond of adenosine 5′-triphosphate. Oxygen-18 enters PRPP by prior exchange of H₂¹⁸O into ribose 5-phosphate; the rate of this exchange was measured by combined gas chromatography-mass spectrometry of the trimethylsilyl derivative of ribose 5-phosphate.     

Acetate Synthesis from H(2) plus CO(2) by Termite Gut Microbes

Gut microbiota from Reticulitermes flavipes termites catalyzed an H(2)-dependent total synthesis of acetate from CO(2). Rates of H(2)-CO(2) acetogenesis in vitro were 1.11 +/- 0.37 mumol of acetate g (fresh weight) h (equivalent to 4.44 +/- 1.47 nmol termite h) and could account for approximately 1/3 of all the acetate produced during the hindgut fermentation. Formate was also produced from H(2) + CO(2), as were small amounts of propionate, butyrate, and lactate-succinate. However, H(2)-CO(2) formicogenesis seemed largely unrelated to acetogenesis and was believed not to be a significant reaction in situ. Little or no CH(4) was formed from H(2) + CO(2) or from acetate. H(2)-CO(2) acetogenesis was inhibited by O(2), KCN, CHCl(3), and iodopropane and could be abolished by prefeeding R. flavipes with antibacterial drugs. By contrast, prefeeding R. flavipes with starch resulted in almost complete defaunation but had little effect on H(2)-CO(2) acetogenesis, suggesting that bacteria were the acetogenic agents in the gut. H(2)-CO(2) acetogenesis was also observed with gut microbiota from Prorhinotermes simplex, Zootermopsis angusticollis, Nasutitermes costalis, and N. nigriceps; from the wood-eating cockroach Cryptocercus punctulatus; and from the American cockroach Periplaneta americana. Pure cultures of H(2)-CO(2)-acetogenic bacteria were isolated from N. nigriceps, and a preliminary account of their morphological and physiological properties is presented. Results indicate that in termites, CO(2) reduction to acetate, rather than to CH(4), represents the main electron sink reaction of the hindgut fermentation and can provide the insects with a significant fraction (ca. 1/3) of their principal oxidizable energy source, acetate.     

Reaction of Bacillus subtilis glutamine phosphoribosylpyrophosphate amidotransferase with oxygen: chemistry and regulation by ligands

The inactivation of glutamine phosphoribosylpyrophosphate amidotransferase by reaction of its iron-sulfur center with O2 is believed to be a physiologically important mode of regulation of this enzyme in Bacillus subtilis cells in the stationary phase of growth. Chemical and physical changes accompanying oxidation of the purified enzyme by O2 were studied. The iron of the 4Fe-4S center was oxidized to enzyme-bound high-spin Fe3+; the S2- was oxidized to a mixture of S0 bound as thiocystine and unidentified products. The oxidant appeared to be O2, rather than peroxide, superoxide, hydroxyl radical, or singlet oxygen. Gross physical changes in the oxidized enzyme were shown by its aggregation, decreased solubility, and altered circular dichroic spectrum. Experimental variables affecting the rate of oxidative inactivation were described; the most important of these was modulation of rates of inactivation by the allosteric inhibitors AMP, ADP, GMP, GDP and by the substrate P-Rib-PP. AMP was a potent stabilizer, whose effect was antagonized by P-Rib-PP. The other nucleotides, either acting singly or acting as synergistic pairs, were destabilizers and able to antagonize stabilization by AMP. The results are discussed in terms of the regulation of the stability of amidotransferase and its degradation in vivo.