Alicyclobacillus acidocaldarius

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]. 

Alicyclobacillus acidocaldarius SC amino acid sequence (amino acids 376 and 377 of the DDTAV motif) are also essential for enzyme activity [59]. These residues are located in the large central cavity of the dimeric enzyme [55]. Interestingly, targeted mutations that convert the DDTAV motif of SC to DCTAE (the corresponding OSC motif) result in a change in substrate specificity from squalene to 2,3-oxidosqualene [61]. 

Comparable studies have been performed for the formation of co-cyclohexyl fatty acids in Alicyclobacillus acidocaldarius and the pathways are identical [100]. A recent publication concerning this later pathway has shown that the final remaining stereochemical ambiguity, the stereochemistry of proton loss at C-6 in the initial 1,4-conjugate elimination of shikimate occurs with loss of the pro-6R proton [102]. This mirrors the stereochemistry of normal shikimate metabolism in the formation of chorismate from 5-enolpyruvyl-shikimate 3-phosphate. 

The syntheses of [5- H] labelled 5-epishikimic acid and [6 H] labelled shikimic acid have been achieved from L-shikimic acid. The synthesis of several deuterated and "C derivatives of shikimic acid has been described in order to study the biosynthesis of ansatrienin (a member of the ansamycin antibiotics). These derivatives were also used in feeding experiments to determine the biosynthesis of the cyclohexanecarboxylic acid starter unit of ca-cyclohexyl fatty acids in Alicyclobacillus acidocaldarius. ... 

Alicyclobacillus Squalene-hopene cyclase (SC). . raveyllscEkdeByI.. mekirryllheBredBt. . ypdvBdBavvvwa.. rraveylkreBkpdBsB.. kaldwveqhBnpdBgB.. acidocaldarius... 

Contamination by Alicyclobacillus spp. was firstly detected in apple juice but, since then, a larger variety of fruit juices, soft drink, fortified with minerals products have been found to be contaminated. A. acidoterrestris and A. acidocaldarius are the most common specie able to cause typical off-fiavors (medicine-like taints) in fruit juices this was related to the production of 2-methoxyphenol (guaiacol), 2-6-dibromophenol, 2-6 diclorophenol [62, 63] which are retained to be the markers of contamination. 

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