Zymomonas mobilis squalene-hopene cyclase gene (shc): cloning, DNA sequence analysis and expression in Escherichia coli

Using a DNA probe from the gene encoding squalene-hopene cyclase (SHC, EC 5.4.99.-) from the Gram-positive bacterium Alicyclobacillus acidocaldarius, we have cloned a 4.3 kb HindIII fragment of chromosomal DNA from Zymomonas mobilis. An open reading frame of 1977 bp was detected that could encode a protein of 658 amino acids with a calculated molecular mass of 74077 Da. Under the control of lac or tac promoters, this gene, shc, was expressed in Escherichia coli K12 strains and its product had squalene-hopene cyclase activity. Sequence alignments with the A. acidocaldarius SHC, the lanosterol cyclase of the yeast Candida albicans, and the cycloartenol synthase of the plant Arabidopsis thaliana revealed six highly conserved regions (mainly in the C-terminal part) of the proteins. These regions contained the core motif Gln-X-X-X-Gly-X-Trp.