期刊
ENVIRONMENTAL MICROBIOLOGY
卷 13, 期 4, 页码 943-959出版社
WILEY
DOI: 10.1111/j.1462-2920.2010.02398.x
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资金
- Ministry of Science and Innovation [BFU2006-15214-C03-01, BFU2009-11545-C03-03]
- Consejo Superior de Investigaciones Cientificas [BFU2006-15214-CO3-01]
P>The first step in the catabolism of cholesterol, i.e. the transformation of cholesterol into cholestenone, has been investigated in Mycobacterium smegmatis. In silico analysis identified the MSMEG_1604 gene encoding a putative protein similar to the ChoD cholesterol oxidase of M. tuberculosis H37Rv (Rv3409c) and the MSMEG_5228 gene coding for a protein similar to the NAD(P)-dependent cholesterol dehydrogenase/isomerase of Nocardia sp. The expression of the MSMEG_5228 gene was inducible by cholesterol whereas the expression of MSMEG_1604 gene was constitutive. When both genes were expressed in Escherichia coli only the MSMEG_5228 protein was active on cholesterol. The function of ChoD-like MSMEG_1604 protein remains to be elucidated, but it does not appear to play a critical role in the mineralization of cholesterol as a MSMEG_1604- mutant was not affected in the production of cholestenone. However, a MSMEG_5228- mutant showed a drastic reduction in the synthesis of cholestenone. The finding that this mutant was still able to grow in cholesterol, allowed us to demonstrate that the cholesterol-inducible MSMEG_5233 gene encodes an additional cholesterol dehydrogenase/isomerase similar to the AcmA dehydrogenase of Sterolibacterium denitrificans. The observation that the double MSMEG_5228-5233- mutant was able to grow in cholesterol suggests that in addition to these enzymes other dehydrogenase/isomerases can also catalyse the first reaction of the cholesterol degradation pathway in M. smegmatis, which is not the limiting step of the process.
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