Fluorescence-based method for selection of recombinant plasmids

A fluorescence-based method for the selection of recombinant plasmids has been developed. Escherichia coli strains bearing plasmids for the overexpression of the gene encoding uroporphyrinogen III methyltransferase (cobA or cysG gene) accumulate fluorescent porphyrinoid compounds. When illuminated with ultraviolet light, the cells fluoresce with a bright red color. Replacement or disruption of the gene with other fragments of DNA results in loss of enzymatic activity and nonfluorescent cells. The detection of the recombinant plasmids can be accomplished without special host strains or expensive chromogenic reagents required for the blue-white screening technique.

Evidence for conformational changes in Escherichia coli porphobilinogen deaminase during stepwise pyrrole chain elongation monitored by increased reactivity of cysteine-134 to alkylation by N-ethylmaleimide

Porphobilinogen deaminase from Escherichia coli becomes progressively more susceptible to inactivation by the thiophilic reagent N-ethylmaleimide (NEM) as the catalytic cycle proceeds through the enzyme-intermediate complexes ES, ES2, ES3, and ES4. Site-directed mutagenesis of potentially reactive cysteines has been used to identify cysteine-134 as the key residue that becomes modified by the reagent and leads to inactivation. Since cysteine-134 is buried at the interface between domains 2 and 3 of the E. coli deaminase molecule, the observations suggest that a stepwise conformational change occurs between these domains during each stage of tetrapyrrole assembly. Interestingly, mutation of the invariant active-site cysteine-242 to serine leads to an enzyme with up to a third of the catalytic activity found in the wild-type enzyme. Electrospray mass spectrometry indicates that serine can substitute for cysteine as the dipyrromethane cofactor attachment site.

The Edinburgh Primary Care Depression Study: personality disorder and outcome

BACKGROUND

Little is known about the impact of personality pathology on the treatment outcome of major depressive illness in primary care in the UK.

METHOD

Patients meeting criteria for DSM-III major depressive disorder were randomly allocated to one of four treatments each lasting 16 weeks, then followed up for 18 months. Assessments were made of depressive symptoms, personality and social functioning. Personality was assessed at maximum improvement or 16 weeks.

RESULTS

The prevalence of personality disorder (PD) in the sample of 113 patients was 26%. Patients with a PD were significantly younger and rated more depressed at entry than patients with no personality disorder (NoPD). On completion of treatment patients with a PD were significantly more depressed and had poorer social functioning than the NoPD group. After 18 months there were no differences in ratings of depression or social functioning between the groups.

CONCLUSIONS

There was substantial improvement in both the PD and NoPD groups. The presence of personality pathology delays recovery from major depressive illness.

Overexpression in Escherichia coli of 12 vitamin B12 biosynthetic enzymes

The first 12 enzymes involved in the biosynthesis of vitamin B12 from its five-carbon precursor, aminolevulinic acid, have been overexpressed in recombinant strains of Escherichia coli. The activity of each enzyme has been demonstrated by the biosynthesis of hydrogenobyrinic acid from aminolevulinic acid.

Cloning, sequencing, and expression of the uroporphyrinogen III methyltransferase cobA gene of Propionibacterium freudenreichii (shermanii)

We cloned, sequenced, and overexpressed cobA, the gene encoding uroporphyrinogen III methyltransferase in Propionibacterium freudenreichii, and examined the catalytic properties of the enzyme. The methyltransferase is similar in mass (27 kDa) and homologous to the one isolated from Pseudomonas denitrificans. In contrast to the much larger isoenzyme encoded by the cysG gene of Escherichia coli (52 kDa), the P. freudenreichii enzyme does not contain the additional 22-kDa peptide moiety at its N-terminal end bearing the oxidase-ferrochelatase activity responsible for the conversion of dihydrosirohydrochlorin (precorrin-2) to siroheme. Since it does not contain this moiety, it is not a likely candidate for synthesis of a cobalt-containing early intermediate that has been proposed for the vitamin B12 biosynthetic pathway in P. freudenreichii. Uroporphyrinogen III methyltransferase of P. freudenreichii not only catalyzes the addition of two methyl groups to uroporphyrinogen III to afford the early vitamin B12 intermediate, precorrin-2, but also has an overmethylation property that catalyzes the synthesis of several tri- and tetra-methylated compounds that are not part of the vitamin B12 pathway. The enzyme catalyzes the addition of three methyl groups to uroporphyrinogen I to form trimethylpyrrocorphin, the intermediate necessary for biosynthesis of the natural products, factors S1 and S3, previously isolated from this organism. A second gene found upstream from the cobA gene encodes a protein homologous to CbiO of Salmonella typhimurium, a membrane-bound, ATP-dependent transport protein thought to be part of the cobalt transport system involved in vitamin B12 synthesis. These two genes do not appear to constitute part of an extensive cobalamin operon.

Frequent deliberate self-harm: repetition, suicide and cost after three or more years

This is a follow-up study of 44 patients who were admitted to the Royal Infirmary of Edinburgh after frequent deliberate self-harm (defined as three or more episodes of deliberate self-harm within one week) at least once between 1982 and 1987. Forty-two patients (95%) were traced after a minimum of three years (range 3yr 1 mo 8yr 9mo). Thirty eight patients were known to have repeated self-harm an average of 13 times during the follow-up. Only two patients had died, one of these by probable suicide. The average cost solely attributable to the in-patient accommodation and psychiatric assessment of this group during follow-up was 34,036.60 pounds (1986-87 prices).

Genetically engineered synthesis of precorrin-6x and the complete corrinoid, hydrogenobyrinic acid, an advanced precursor of vitamin B12

BACKGROUND

Genetically engineered synthesis, in which the gene products, cofactors, and substrates of a complete pathway are combined in vitro in a single flask to give the target, can be a viable alternative to conventional chemical construction of molecules of complex structure and stereochemistry. We chose to attempt to synthesize the metal-free corrinoid hydrogenobyrinic acid, an advanced precursor of vitamin B12.

RESULTS

Cloning and overexpression of the genes necessary for the S-adenosyl methionine dependent conversion of 5-aminolevulinic acid (ALA) to precorrin-3 and those required for the synthesis of hydrogenobyrinic acid from precorrin-3 completed the repertoire of the 12 biosynthetic enzymes involved in corrin synthesis. Using these enzymes and the necessary cofactors, the multi-enzyme synthesis of hydrogenobyrinic acid from ALA can be achieved in 20% overall yield in a single reaction vessel, corresponding to an average of at least 90% conversion for each of the 17 steps involved.

CONCLUSIONS

By replacing the cell wall with glass, and by mixing the soluble biosynthetic enzymes and necessary cofactors, the major segment of the physiological synthesis of vitamin B12 has been accomplished. Since only those enzymes necessary for the synthesis of hydrogenobyrinic acid from ALA are supplied, none of the intermediates is deflected from the direct pathway. This results in an efficiency which in fact surpasses that of nature.

Gene dissection demonstrates that the Escherichia coli cysG gene encodes a multifunctional protein

The C-terminus of the Escherichia coli CysG protein, consisting of amino acids 202-457, was expressed as a recombinant protein using gene dissection methodology. Analysis of the activity of this truncated protein, termed CysGA, revealed that it was able to methylate uroporphyrinogen III in the same S-adenosyl-L-methionine (SAM)-dependent manner as the complete CysG protein. However, this truncated protein was not able to complement E. coli cysG cells, thereby suggesting that the first 201 amino acids of the CysG protein had an enzymic activity associated with the conversion of dihydrosirohydrochlorin into sirohaem. Analysis of the N-terminus of the CysG protein revealed the presence of a putative pyridine dinucleotide binding site. When the purified CysG protein was incubated with NADP+, uroporphyrinogen III and SAM the enzyme was found to catalyse a coenzyme-mediated dehydrogenation to form sirohydrochlorin. The CysGA protein on the other hand showed no such coenzyme-dependent activity. Analysis of the porphyrinoid material isolated from strains harbouring plasmids containing the complete and truncated cysG genes suggested that the CysG protein was also involved in ferrochelation. The evidence presented in this paper suggests that the CysG protein is a multifunctional protein involved in SAM-dependent methylation, pyridine dinucleotide dependent dehydrogenation and ferrochelation.

Genetically engineered synthesis of natural products

The feasibility of multi-step, one-flask total synthesis of natural products is demonstrated by cloning and overexpression of the corresponding biosynthetic enzymes from plant and microbial sources. As many as eight or nine enzymes can be recombined in vitro to reach an advanced intermediate in the vitamin B12 pathway.

Contemporary practice of electroconvulsive therapy

Electroconvulsive therapy (ECT) is an effective and important treatment for severe depressive illness and for other depressive illnesses that have not responded to drug treatment. Practical guidelines based on recent research findings are presented here to maximize the efficacy and minimize the adverse effects of ECT.

19-Bromo-1-hydroxymethylbilane, a novel inhibitor of uro'gen III synthase

A novel hydroxymethylbilane analog, 19-Br-HMB (11), has been synthesized. Its activity with the enzyme Uro'gen III synthase shows competitive inhibition.

Evidence for an intermediate in the enzymatic formation of uroporphyrinogen III

Evidence for an azafulvene intermediate in the enzymatic formation of Uroporphyrinogen III has been obtained. Using conditions to slow down the enzyme activity (high pH, low temperature), the transient species was trapped with ammonium ions as aminomethylbilane and with sodium borohydride as methylbilane, and observed by 13C-NMR.

Is there a delay in the onset of the antidepressant effect of electroconvulsive therapy?

The severity of depression in 11 drug-free unipolar patients diagnosed with definite major depressive disorder was assessed using the Hamilton Rating Scale for Depression during a course (5-10 treatments) of bilateral electroconvulsive therapy (ECT). The degree of improvement after three treatments of ECT was six times greater than the improvement that occurred over the remainder of the course. Although depressed patients who recover with ECT require repeated treatments, the treatments early in a course of ECT can have marked antidepressant effect.

NMR and molecular modeling study of active and inactive taxol analogues in aqueous and nonaqueous solution

The conformations of the biologically active taxol analogs Taxotere®, 3R, 4R, and 4S, and the biologically inactive analog 3S were evaluated in CDCl3 and DMSO–water solution using 1H NMR coupling constant and NOESY data and molecular modeling. The solution structures of Taxotere® were very similar to those detected previously for taxol. The A-ring side chain conformations of analogs 3 and 4 could not be defined with the same precision as had been possible for taxol, but the conformational possibilities could be significantly limited by the data. Analogs 3R, 4R, and 4S (but not 3S) can mimic the dominant conformation of taxol in chloroform, but no logical relationship between biological activity and aqueous solution conformation could be detected.

Short-term effects of electroconvulsive treatment on the uptake of 99mTc-exametazime into brain in major depression shown with single photon emission tomography

Fifteen patients with major depression who were being treated with bilateral electroconvulsive treatment (ECT) were investigated before and 45 min after a single ECT using split-dose Single Photon Emission Tomography (SPET or SPECT) with 99mTc-Exametazime. All patients suffered from unipolar depressive illness and were rated on the Newcastle scale and with the 17-item Hamilton scale. They completed tests of orientation and verbal memory on the day of ECT. For comparison, verbal memory was also tested on the preceding day. The uptake of 99mTc-Exametazime was expressed relative to calcarine/occipital cortex. Significant decreases in tracer uptake were confined to the inferior anterior cingulate cortex. The changes were correlated with the severity of depressive symptoms and more weakly with decrements of memory function produced by ECT; there was no significant correlation with stimulus intensity or electroencephalographic measures of seizure duration.

The Escherichia coli cysG gene encodes the multifunctional protein, siroheme synthase

Previously, the E. coli cysG gene product had been shown to sequentially methylate uro'gen III to produce precorrin-2, hence it was given the trivial name uro'gen III methylase. We now report that in addition to methylase activity, the CysG protein catalyses both the NAD+ dependent oxidation of precorrin-2 to sirohydrochlorin, but also the insertion of iron into this oxidized intermediate, thereby producing siroheme. Thus CysG is a multifunctional protein solely responsible for siroheme synthesis from uro'gen III in E. coli, and accordingly is renamed siroheme synthase.

Biosynthesis of vitamin B12. Discovery of the enzymes for oxidative ring contraction and insertion of the fourth methyl group

In the vitamin B12 biosynthetic pathway the enzymes responsible for the conversion of precorrin-3 to precorrin-4 have been identified as the gene products of cobG and cobJ from Pseudomonas denitrificans. CobG catalyzes the oxidation of precorrin-3 to precorrin-3x (a hydroxy lactone) whereas CobJ is a SAM-dependent C-17 methyl transferase and is necessary for ring contraction. A mechanism for ring contraction is proposed.