A. Bellamine et al., Structural requirements for substrate recognition of Mycobacterium tuberculosis 14 alpha-demethylase: implications for sterol biosynthesis, J LIPID RES, 42(1), 2001, pp. 128-136
Sterol 14 alpha -demethylase (14DM) is a cytochrome P-450 involved in stero
l biosynthesis in eukaryotes, It was reported that Mycobacterium smegmatis
also makes cholesterol and that cholesterol is essential to Mycobacterium t
uberculosis (MT) infection, although the origin of the cholesterol is unkno
wn. A protein product from MT having about 30% sequence identity with eukar
yotic 14 alpha -demethylases has been found to convert sterols to their 14-
demethyl products indicating that a sterol pathway might exist in MT: To de
termine the optimal sterol structure recognized by MT 14DM, binding of 28 s
terol and sterol-like (triterpenoids) molecules to the purified recombinant
14 alpha -demethylase was examined, Like eukaryotic forms, a 3 beta -hydro
xy group and a 14 alpha -methyl group are essential for substrate acceptabi
lity by the bacterial 14 alpha -demethylase. The high affinity binding of 3
1-norcycloartenol without detectable activity indicates that the Delta (8)-
bond is required for activity but not for binding. As for plant 14 alpha -d
emethylases, 31-nor-sterols show a binding preference for MT 14DM, Similar
to enzymes from mammals and yeast, a C24-alkyl group is not required for MT
14DM binding and activity, whereas it is for plant 14 alpha -demethylases.
Thus, substrate binding to MT 14DM seems to share common features with all
eukaryotic 14 alpha -demethylases, the MT form seemingly having the broade
st substrate recognition of all forms of 14 alpha -demethylase studied so f
ar.