Polyprenyl Phosphate Biosynthesis in Mycobacterium tuberculosis and Mycobacterium smegmatis

Mycobacterium smegmatis has been shown to contain two forms of polyprenyl phosphate (Pol-P), while Mycobacterium tuberculosis contains only one. Utilizing subcellular fractions from M. smegmatis and M. tuberculosis, we show that Pol-P synthesis is different in these species. The specific activities of the prenyl diphosphate synthases in M. tuberculosis are 10- to 100-fold lower than those in M. smegmatis. In M. smegmatis decaprenyl diphosphate and heptaprenyl diphosphate were the main products synthesized in vitro, whereas in M. tuberculosis only decaprenyl diphosphate was synthesized. The data from both organisms suggest that geranyl diphosphate is the allylic substrate for two distinct prenyl diphosphate synthases, one located in the cell membrane that synthesizes ω,E,Z-farnesyl diphosphate and the other present in the cytosol that synthesizes ω,E,E,E-geranylgeranyl diphosphate. In M. smegmatis, the ω,E,Z-farnesyl diphosphate is utilized by a membrane-associated prenyl diphosphate synthase activity to generate decaprenyl diphosphate, and the ω,E,E,E-geranylgeranyl diphosphate is utilized by a membrane-associated activity for the synthesis of the heptaprenyl diphosphate. In M. tuberculosis, however, ω,E,E,E-geranylgeranyl diphosphate is not utilized for the synthesis of heptaprenyl diphosphate. Thus, the difference in the compositions of the Pol-P of M. smegmatis and M. tuberculosis can be attributed to distinct enzymatic differences between these two organisms.

已有研究表明，耻垢分枝杆菌（Mycobacterium smegmatis）含有两种形式的聚异戊烯磷酸（polyprenyl phosphate, Pol-P），而结核分枝杆菌（Mycobacterium tuberculosis）仅含一种。本研究利用耻垢分枝杆菌与结核分枝杆菌的亚细胞组分，证实二者的Pol-P合成过程存在差异。结核分枝杆菌的异戊二烯二磷酸合酶（prenyl diphosphate synthases）比活性较耻垢分枝杆菌低10~100倍。体外实验中，耻垢分枝杆菌的主要合成产物为癸异戊烯二磷酸（decaprenyl diphosphate）与七异戊烯二磷酸（heptaprenyl diphosphate），而结核分枝杆菌仅能合成癸异戊烯二磷酸。对两种菌株的研究数据均显示，香叶基二磷酸（geranyl diphosphate）可作为两种不同异戊二烯二磷酸合酶的烯丙基底物：一种定位于细胞膜，负责合成ω,E,Z-法尼基二磷酸（ω,E,Z-farnesyl diphosphate）；另一种存在于细胞质基质，负责合成ω,E,E,E-香叶基香叶基二磷酸（ω,E,E,E-geranylgeranyl diphosphate）。在耻垢分枝杆菌中，膜结合的异戊二烯二磷酸合酶可利用ω,E,Z-法尼基二磷酸合成癸异戊烯二磷酸，而另一膜结合酶则利用ω,E,E,E-香叶基香叶基二磷酸合成七异戊烯二磷酸。但在结核分枝杆菌中，ω,E,E,E-香叶基香叶基二磷酸无法用于七异戊烯二磷酸的合成。综上，耻垢分枝杆菌与结核分枝杆菌的Pol-P组成差异，可归因于二者之间存在的特异性酶学差异。