Mosquito larvicidal activity of silver nanoparticles synthesised using actinobacterium, Streptomyces sp. M25 against Anopheles subpictus, Culex quinquefasciatus and Aedes aegypti

The present work reports the larvicidal potential of microbially synthesised silver nanoparticles (AgNPs) by using an actinobacterium, Streptomyces sp. M25 isolated from Western Ghats, Tamil Nadu, India. The biomass of Streptomyces sp. was exposed to 1 mM silver nitrate (AgNO3) solution. The synthesis of AgNPs was confirmed by visual inspection followed by instrumental analysis such as UV-vis spectroscopy, fourier transform infrared spectroscopy, X-ray diffraction (XRD), energy dispersive X-ray spectroscopy, scanning electron microscopy, atomic force microscopy and transmission electron microscopy (TEM) with selected area electron diffraction. Based on the TEM and XRD analysis, the average size of the AgNPs was determined to be 10-35 nm. The biosynthesised AgNPs exhibited significant larvicidal activity against malarial vector, Anopheles subpictus (LC50 51.34 mg/L and χ (2) value of 8.228), filarial vector, Culex quinquefasciatus (LC50 48.98 mg/L and χ (2) value of 14.307) and dengue vector, Aedes aegypti (LC50 60.23 mg/L and χ (2) value of 4.042), respectively. Similarly, AgNO3 had larvicidal activity against malarial vector, A. subpictus (LC50 42.544 mg/L and χ (2) value of 2.561), filarial vector, C. quinquefasciatus (LC50 44.922 mg/L and χ (2) value of 1.693) and dengue vector, A. aegypti (LC50 39.664 mg/L and χ (2) value of 5.724), respectively. The current study is a rapid, cost effective, eco-friendly and single step approach. The Streptomyces sp. M25 is a newly added source for the synthesis of AgNPs with improved larvicidal activity.

Identification of a cysteine involved in the interaction between carbon monoxide dehydrogenase and corrinoid/Fe-S protein from Clostridium thermoaceticum

In Clostridium thermoaceticum, the synthesis of acetyl-CoA from methyl tetrahydrofolate occurs via a series of enzymatic reactions involving methyl transferase, corrinoid/Fe-S protein (corrinoid), carbon monoxide dehydrogenase (CODH) and ferredoxin. We have investigated the possibility of one or more of these proteins existing as multi-enzyme complexes in vivo with higher catalytic activity. A protein complex consisting of CODH and corrinoid was isolated from the cell-free extracts of Clostridium thermoaceticum. The acetyl-CoA synthesis was found to be approximately 1.8-fold higher with the complex than that observed with the isolated protein components. HPLC gel filtration analyses of the native and DTE reduced complex suggested that the CODH:corrinoid complex is held together primarily by an inter disulfide bond. By differential labeling of thiols with [14C]N-ethylmaleimide it was found that Cys-506 of the alpha subunit of CODH was involved in the disulfide linkage with the corrinoid of the complex.

Interaction of ferredoxin with carbon monoxide dehydrogenase from Clostridium thermoaceticum

Acetogenic bacteria, as determined with Clostridium thermoaceticum, synthesize acetate by the acetyl-CoA pathway which involves the reduction of CO2 to a methyl group and then combination of the methyl with CoA and a carbonyl group formed from CO or CO2 (Wood, H.G., Ragsdale, S.W., and Pezacka, E. (1986) Trends Biochem. Sci. 11, 14-18). Carbon monoxide dehydrogenase (CODH), the key enzyme in this pathway not only catalyzes the oxidation of CO to CO2 but also the final step, the synthesis of acetyl-CoA from a methyl group, CO, and CoA. Previously, it has been shown that ferredoxin can stimulate exchange of CO with CH3 14COSCoA (Ragsdale, S.W., and Wood, H.G. (1985) J. Biol. Chem. 260, 3970-3977). In the present study, it has been observed that ferredoxin and CODH can form an electrostatically stabilized complex. In order to identify the ferredoxin binding region on CODH, the ferredoxin and CODH were cross-linked by using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. The cross-linked CODH-ferredoxin adduct was enzymatically as active as the uncross-linked complex. The native CODH and cross-linked CODH-ferredoxin complex were subjected to cyanogen bromide cleavage. By comparison of the high-performance liquid chromatography peptide profiles, it was observed that the mobility of at least one peptide is altered in the CODH-ferredoxin cross-linked complex. The peptide was identified with residues 229-239 of the alpha-subunit of CODH.

The primary structure of the subunits of carbon monoxide dehydrogenase/acetyl-CoA synthase from Clostridium thermoaceticum

CO dehydrogenase/acetyl-coenzyme A synthase (CODH) is the central enzyme in the pathway of acetyl-coenzyme A biosynthesis in Clostridium thermoaceticum. It catalyzes the interconversion of CO and CO2 and the synthesis of acetyl-coenzyme A from the methylated corrinoid/iron sulfur protein, CO, and coenzyme A. It is a nickel-iron-sulfur protein and contains two subunits in the form (alpha beta)3. Reported here is the cloning and sequencing of the genes for both subunits of CODH. The gene for the alpha subunit codes for a protein with 729 amino acids and a molecular weight of 81,730, and the beta gene for a protein with 674 amino acids and a molecular weight of 72,928. The alpha subunit follows the beta subunit by 23 bases and the genes for both subunits are preceded by a sequence which is similar to the Shine-Dalgarno sequence of Escherichia coli. No significant amino acid sequence homology has been found to any known sequence. Labeling CODH with 2,4-dinitrophenylsulfenyl chloride and isolating labeled peptide fragments demonstrated that a tryptophan, residue 418 of the alpha subunit, is protected by coenzyme A and thus may be considered a potential part of the coenzyme A site.

Chemical modification of the functional arginine residues of carbon monoxide dehydrogenase from Clostridium thermoaceticum

Carbon monoxide dehydrogenase (CODH) is the key enzyme of autotrophic growth with CO or CO2 and H2 by the acetyl-CoA pathway. The enzyme from Clostridium thermoaceticum catalyzes the formation of acetyl-CoA from the methyl, carbonyl, and CoA groups and has separate binding sites for these moieties. In this study, we have determined the role of arginine residues in binding of CoA by CODH. Phenylglyoxal, an arginine-specific reagent, inactivated CODH, and CoA afforded about 80-85% protection against this inactivation. The other ligands, such as the carbonyl and the methyl groups, gave no protection. By circular dichroism, it was shown that the loss of activity is not due to extensive structural changes in CODH. Earlier, we showed that tryptophan residues are located at the CoA binding site of CODH [Shanmugasundaram, T., Kumar, G. K., & Wood, H. G. (1988) Biochemistry 27, 6499-6503]. A comparison of the fluorescence spectra of the native and phenylglyoxal-modified enzymes indicates that the reactive arginine residues appear to be located close to fluorescing tryptophans. Fluorescence spectral studies with CoA analogues or its components showed that CoA interacts with the tryptophan(s) of CODH through its adenine moiety. In addition, evidence is presented that the arginines interact with the pyrophosphate moiety of CoA.

Involvement of tryptophan residues at the coenzyme A binding site of carbon monoxide dehydrogenase from Clostridium thermoaceticum

Carbon monoxide dehydrogenase (CODH) from Clostridium thermoaceticum plays a central role in the newly discovered acetyl-CoA pathway [Wood, H.G., Ragsdale, S.W., & Pezacka, E. (1986) FEMS Microbiol. Rev. 39, 345-362]. The enzyme catalyzes the formation of acetyl-CoA from methyl, carbonyl, and CoA groups, and it has specific binding sites for these moieties. In this study, we have determined the role of tryptophans at these subsites. N-Bromosuccinimide (NBS) oxidation of the exposed and reactive tryptophans (5 out of a total of approximately 20) of CODH at pH 5.5 results in the partial inactivation of the exchange reaction (approximately 50%) involving carbon monoxide and the carbonyl group of the acetyl-CoA. Also, about 70% of the acetyl-CoA synthesis was abolished as a result of NBS modification. The presence of CoA (10 microM) produced complete protection against the partial inhibition of the exchange activity and the overall synthesis of acetyl-CoA caused by NBS. Additionally, none of the exposed tryptophans of CODH was modified in the presence of CoA. Ligands such as the methyl or the carbonyl groups did not afford protection against these inactivations or the modification of the exposed tryptophans. A significant fraction of the accessible fluorescence of CODH was shielded in the presence of CoA against acrylamide quenching. On the basis of these observations, it appears that certain tryptophans are involved at or near the CoA binding site of CODH.

Role of carbon monoxide dehydrogenase in acetate synthesis by the acetogenic bacterium, Acetobacterium woodii

Carbon monoxide dehydrogenase (CODH) plays a key role in acetate synthesis by the acetogenic bacterium, Clostridium thermoaceticum. Acetobacterium woodii, like C. thermoaceticum contains high levels of CODH. In this work we show that crude extracts of A. woodii synthesize acetate from methyl tetrahydrofolate or methyl iodide, carbon monoxide and coenzyme A (CoA). The purified CODH from A. woodii catalyzes an exchange reaction between CO and the carbonyl group of acetyl-CoA even faster than the C. thermoaceticum enzyme, indicating the CODH of A. woodii, like that of C. thermoaceticum is an acetyl-CoA synthetase. Fluorescence and EPR studies further support this postulate by demonstrating that CODH binds CoA near the CO binding site involving a tryptophan residue. The UV absorption spectra and the amino acid compositions of A. woodii and C. thermoaceticum CODHs are very similar. Evidence is presented using purified enzymes from A. woodii that the synthesis of acetyl-CoA occurs by a pathway similar to that utilized by C. thermoaceticum.