Catalysis using iron–sulfur clusters and transition metals can be traced back to the last universal common ancestor. The damage to metalloproteins caused by reactive oxygen species (ROS) can prevent cell growth and survival when unmanaged, thus eliciting an essential stress response that is universal and fundamental in biology. Here we develop a computable multiscale description of the ROS stress response inEscherichia coli, called OxidizeME. We use OxidizeME to explain four key responses to oxidative stress: 1) ROS-induced auxotrophy for branched-chain, aromatic, and sulfurous amino acids; 2) nutrient-dependent sensitivity of growth rate to ROS; 3) ROS-specific differential gene expression separate from global growth-associated differential expression; and 4) coordinated expression of iron–sulfur cluster (ISC) and sulfur assimilation (SUF) systems for iron–sulfur cluster biosynthesis. These results show that we can now develop fundamental and quantitative genotype–phenotype relationships for stress responses on a genome-wide basis.

As part of our continuing search for potential anticancer drug candidates in the 2-aryl-1,8-naphthyridin-4(1H)-one series, we have synthesized two series of 3'-substituted 2-phenyl-1,8-naphthyridin-4(1H)-ones and 2-naphthyl-1,8-naphthyridin-4(1H)-ones. All compounds showed significant cytotoxic effects (log GI50 < -4.0; log molar drug concentration required to cause 50% growth inhibition) against a variety of human tumor cell lines of the National Cancer Institute's in vitro screen, including cells derived from solid tumors such as non-small cell lung, colon, central nervous system, melanoma, ovarian, prostate, and breast cancers. All 3'-substituted compounds demonstrated strong cytotoxic effects in almost all tumor cell lines. Introduction of an aromatic ring at the 2'- and 3'-positions also generated compounds with potent antitumor activity. Incorporation of an aromatic ring at the 3'- and 4'-positions produced compounds with reduced activity. Interestingly, introduction of a halogen at the 3'-position yielded compounds with different selectivity for the tumor cell lines tested. All 3'-halogenated compounds (29-36) and compounds 38 and 42-44 were potent inhibitors of tubulin polymerization with activities nearly comparable to those of the potent antimitotic natural products colchicine, podophyllotoxin, and combretastatin A-4. Active agents also inhibited the binding of [3H]colchicine to tubulin.

Herein, the cytocompatibility of selected MAX phases, Ti3AlC2, Ti3SiC2, and Ti2AlN, were systematically evaluated using in vitro tests for the first time. These phases were anoxic to preosteoblasts and fibroblasts. Compared with the strong viable fibroblasts, the different cellular responses of these materials were clearly distinguishable for the preosteoblasts. Under an osteoblastic environment, Ti2AlN exhibited better cell proliferation and differentiation performance than Ti3AlC2 and Ti3SiC2. Moreover, the performance was superior to that of a commercial Ti–6Al–4V alloy and comparable to that of pure Ti. A possible mechanism was suggested based on the different surface oxidation products, which were determined from the binding energy of adsorbed Ca2+ ions using first-principles calculations. Compared with the partially oxidized TiC x O y layer on Ti3AlC2 and Ti3SiC2, the partially oxidized TiN x O y layer on the Ti2AlN had a stronger affinity to the Ca2+ ions, which indicated the good cytocompatibility of Ti2AlN.

7-O-Substituted analogues of allothiocochicine were synthesized and evaluated for their inhibitory effects on tubulin polymerization in vitro. Ketone 6, a key compound in this study, was derived from thiocolchicone 5 by ring contraction. The structure of 6 was determined from spectral data. Optically active alcohols 7a and 7b were obtained by reduction of ketone 6 followed by chemical resolution including a separation of the camphanate diastereomers 8a and 8b and basic hydrolysis. The aR,7R configuration of 8b was verified by X-ray crystallographic analysis. Almost all compounds had strong inhibitory effects on the tubulin polymerization reaction, with IC50 values from 1.7 to 9.0 μM. The camphanates, cyclohexanates, and, most notably, the 7S-benzoate ester (10a), were inactive with IC50 values >40 μM. Compounds 6 and 7a also showed potent antitumor activity with GI50 values at nM concentration range for most cell lines in NCI's in vitro screening. Generally, the 7S enantiomers of colchicinoids with a troplone C-ring showed greater activity than the 7R enantiomers. In the current allothiocolchicinoid (with a benzenoid C-ring) study, only small differences occurred between the two active enantiomers of each pair. The acyl esters with a 7S configuration were slightly more active than the 7R isomers. However, the aroyl ester with a 7S configuration was less active than the 7R isomer. NMR, optical rotation, and molecular modeling studies revealed two conformers in a solvent-dependent equilibrium for both 7S and 7R isomers. In polar solvents, the molecular chirality in esters with a 7-O-aroyl substituent was reversed from aS to aR or from aR to aS at an intensified rate.

Dedicated to Prof. Dieter Seebach on the occasion of his 60th birthday 7-0-Substituted analogs of deaminodeoxycolchinol thiomethyl ether were synthesized and evaluated for their inhibitory effects on tubulin polymerization in vitro. Ketone 9, a key compound in this study, was derived from thiocolchicone 6 by reaction with aniline. Reaction of compound 6 with MeNH, or BuNH, gave tetracyclic lactams 7 and 8, respectively. Optically active alcohols l l a and l l b were obtained from racemic 11 by chemical resolution including a separation of the camphanate diastereoisomers 12a and lZb, followed by basic hydrolysis. The (aR,7R)-configuration of 12b was verified by X-ray crystallographic analysis. Almost all racemic and optically active 7-0-acyl or 7-0-aroyl compounds had strong inhibitory effects on the tubulin polymerization reaction, with ZC,, values from 1.7 to 5.1 p~. A few agents, such as the lactams 7 and 8, the camphanates 12a and 12b, the cyclohexanecarboxylates 19a and 19b, and, most notably, the (7s)-benzoate 15a, had negligible effects on polymerization, yielding IC,, values greater than 40 p~. Ketone 9 showed strong inhibition of tubulin polymerization comparable to that of thiocolchicone (6). Optically active alcohol l l a and acyl esters 13a and 14a with a (7S)-configuration were more active than the (7R)-esters 13b and 14b. However, the esters 15a-17a with a (7S)-configuration were less active than the (7R)-isomers 15b-l7b, in which the (7R)-benzoate 15b was at least 15-fold more inhibitory than the (7S)-isomer 15a. For the most part, the agents causing strongest inhibition of polymerization also caused the greatest inhibition of ['H]colchicine binding. NMR and optical rotatory data indicate that, in polar solvents, the equilibrium in esters with a 7-0-aroyl substituent, i.e., 15a,b, 16a,b, and 17a,b, is reversed from (as) to (aR) or from (aR) to (as), as compared to nonpolar solvents. I)

In the biosynthesis of pentalenolactone (1), PenE and PntE, orthologous proteins from Streptomyces exfoliatus and S. arenae, respectively, catalyze the flavin-dependent Baeyer-Villiger oxidation of 1-deoxy-11-oxopentalenic acid (4) to the lactone pentalenolactone D (5), in which the less-substituted methylene carbon has migrated. By contrast, the paralogous PtlE enzyme from S. avermitilis catalyzes the oxidation of 4 to neopentalenolactone D (6), in which the more substituted methane substitution has undergone migration. We report the design and analysis of 13 single and multiple mutants of PntE mutants in order to identify the key amino acids that contribute to the regiospecificity of these two classes of Baeyer-Villiger monooxygenases. The L185S mutation in PntE reversed the observed regiospecificity of PntE such that all recombinant PntE mutants harboring this L185S mutation acquired the characteristic regiospecificity of PtlE, catalyzing the conversion of 4 to 6 as the major product. The recombinant PntE mutant harboring R484L exhibited reduced regiospecificity, generating a mixture of lactones containing more than 17% of 6. These in vitro results were corroborated by analysis of the complementation of the S. avermitilis ΔptlED double deletion mutant with pntE mutants, such that pntE mutants harboring L185S produced 6 as the major product, while complemention of the ΔptlED deletion mutant with pntE mutants carrying the R484L mutation gave 6 as more than 33% of the total lactone product mixture.

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BackgroundHuman tissue plasminogen activator (tPA) belongs to the serine protease family. It converts plasminogen into plasmin and is used clinically to treat thrombosis. Human tPA is composed of 527 amino acids residues and contains 17 disulfide bonds. Escherichia coli has been used only rarely for the efficient production of recombinant tPA. However, the functional expression of full-length tPA that contains multiple disulfide bonds on an industrial scale remains challenging. Here, we describe the soluble expression and characterization of full-length tPA by auto-induction in E. coli.ResultsWe achieved optimal levels of gene expression, minimized negative effects related to the production of heterologous proteins, and optimized cytoplasmic yields. Three different E. coli strains, BL21 (DE3), Rosetta, and Origami 2, could express tPA using an auto-induction mechanism. In addition, similar yields of recombinant protein were produced at temperatures of 33, 35, and 37°C. The E. coli strain origami 2 could increase disulfide bond formation in cytoplasmic tPA and produce purified soluble recombinant protein (~0.9 mg/l medium). The full-length tPA was monomeric in solution, and fibrin plate assays confirmed that the recombinant tPA displayed serine protease activity.ConclusionsThis is the first report that describes the heterologous expression of correctly folded active full-length tPA. This could provide valuable information for using prokaryotic auto-induction expression systems to produce tPA at industrial and pharmaceutical levels without in vitro refolding during the production step.