Acidocaldarius

Figure 5.28 Enantioselective hydrolysis of sulfate esters using S. acidocaldarius.

The Rieske protein II (SoxF) from Sulfolobus acidocaldarius, which is part, not of a bci or b f complex, but of the SoxM oxidase complex 18), could be expressed in E. coli, both in a full-length form containing the membrane anchor and in truncated water-soluble forms 111). In contrast to the results reported for the Rieske protein from Rhodobacter sphaeroides, the Rieske cluster was more efficiently inserted into the truncated soluble forms of the protein. Incorporation of the cluster was increased threefold when the E. coli cells were subject to a heat shock (42°C for 30 min) before induction of the expression of the Rieske protein, indicating that chaperonins facilitate the correct folding of the soluble form of SoxF. The iron content of the purified soluble SoxF variant was calculated as 1.5 mol Fe/mol protein the cluster showed g values very close to those observed in the SoxM complex and a redox potential of E° = +375 mV 111). 

Fig. 2. Protein backbone representations of (a) the 2[4Fe-4S] ferredoxin from Peptococcus aerogenes, (b) the proposed structure of the FA/FB-binding protein of PSl based on the 4 A crystsd structure (25), and (c) the [3Fe-4S][4Fe-4S] ferredoxin from Sulfolo-bus acidocaldarius. Ligands to clusters Fa and Fb, important residues as well as the loop extension (see text) EU e highlighted in darker gray.

To date, only two exceptions to the pK of 8 rule have been found the Rieske protein from Sulfolobus acidocaldarius (139) and that from Thiobacillus ferrooxidans (140). In both cases, a first pK is observed in the vicinity of 6 (Fig. 7). The fact that Sulfolobus and Thiobacillus are phylogenetically almost as distant as they can possibly be, but share acidophilic growth conditions (medium-pH of 2), indicates that the pK, which is lower by 2 pH units in Sulfolobus and Thiobacillus, reflects adaptation. In the absence of structural information for the two acidophilic Rieske proteins, the molecular modifications resulting in this pK shift are difficult to guess. The absence of sequence data for the Thiobacillus protein furthermore precludes a comparative approach. It seems likely, however, that the solvent-exposed histidine ligands to the cluster will become slightly more bur-... 

Reports on a few other desulfurization organisms also exists, including Nocardia [98], S. acidocaldarius [5,99], Arthrobacter [100], R. toruloides, [101], C. elegans [102], Klebsiella spp. [103], and Alcaligenes xylosoxydans strain deposited with the ATCC under PTA-4669 [104], A S. acidocaldarius species was reported to desulfurize DBT and produce sulfate [5], A similar strain was later used to study the DBT desulfurization [99] in complex media using tryptone however, the authors reported that the strain was not active when grown on sucrose. It was apparently inhibited by DBT and also affected by the interface in oil-water mixtures [105],... 

Kargi, F., and Robinson, J. M., Microbial Oxidation of Dibenzothiophene by the Thermophilic Organism Sulfolobus Acidocaldarius. Biotechnology and Bioengineering, 1984. 26 p. 687. 

Kankipati, P., and Ju, L. K., Microbial Desulfurization of Petroleum Fundamental Study on Dibenzothiophene Desulfurization by Sulfolobus Acidocaldarius. In Exploration Issues and Solutions in Petroleum Exploration, Production and Refining. 1994. Pennwell Books. 605-614. 

Figure 29 Cyclic voltammogram recorded at an edge-orientedpyrolitic graphite electrode in an aqueous solution (pH 6.4) of the 7Fe ferredoxin of Sulfolabus acidocaldarius in the presence of neomicin sulfate...

Bartolucci, S., A. Guagliardi, E. Pedone, D. De Pascale, R. Cannio, L. Camardella, M. Rossi, G. Nicastro, C. de Chiara, P. Facci, G. Mascetti, and C. Nicolini. 1997. Thioredoxin from Bacillus acidocaldarius characterization, high-level expression in Escherichia coli and molecular modelling. Biochem J 328 277-285. 

The solution structure of a thioredoxin from B. acidocaldarius (Topt = 60 °C) has been studied by NMR and compared with that of E. coli determined by X-ray analysis. It was found that the higher thermostability of the former is due to cumulative effects, the main factor being an increased number of ionic interactions cross-linking different secondary structural elements. Multidimensional heteronuclear NMR spectroscopy was also employed to characterize thioredoxin homologues found in the hyperthermophilic... 

In recent years, several papers appeared in the literature concerning NMR and X-ray studies of thermostable ribonucleases. Among archaebacteria, several histone-like proteins from Sulfolobus strains have been identified and grouped into molecular mass classes. From the 7 kDa class, Sac7e from S. acidocaldarius and Sso7d from S. solfataricus, possessing DNA binding activity in combination with non-specific RNase activity, were identified. ... 

In the context of the desirability of removing sulfur compounds from fuels, a bacterial strain has been identified that will metabolize thianthrene to water-soluble products under aerobic conditions (83MI5). A thermophilic organism, Sulfolobus acidocaldarius, removed 38% of the sulfur, as measured by sulfate release, in 4 weeks at 70°C (87MI2). 

Currently there is no experimentally determined three-dimensional structural information available for OSCs, although studies with a related enzyme, squa-lene-hopene cyclase (SC EC 5.4.99.7) have proved informative. SCs are involved in the direct cyclisation of squalene to pentacyclic triterpenoids known as hopanoids, which play an integral role in membrane structure in prokaryotes [ 51 ]. A number of SC genes have been cloned from bacteria [52 - 54]. The SC and OSC enzymes have related predicted amino acid sequences, and so should have similar spatial structures [55]. The crystal structure of recombinant SC from the Gram-positive bacterium Alicyclobacillus acidocaldarius has established that the enzyme is dimeric [55]. Each subunit consists of two a-a barrel domains that assemble to form a central hydrophobic cavity [55,56]. 

The activity of 2,3-oxidosqualene cyclases is associated with microsomes, indicating their membrane-bound nature. However, the predicted amino acid sequences of these enzymes generally lack signal sequences and obvious transmembrane domains. Addition of hydrophobic membrane-localising regions to OSCs during evolution may have removed selection pressures that maintained alternate mechanisms for membrane localisation [33]. Consistent with this, there is a non-polar plateau on the surface of the A. acidocaldarius SC enzyme which is believed to be immersed in the centre of the membrane. The squalene substrate for SC is likely to diffuse from the membrane interior into the central cavity of the enzyme via this contact region [55,56]. 

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