ABSTRACT
Mycobacterium tuberculosis
utilizes the methylerythritol phosphate (MEP) pathway for biosynthesis of isopentenyl diphosphate and its isomer, dimethylallyl diphosphate, precursors of all isoprenoid compounds. This pathway is of interest as a source of new drug targets, as it is absent from humans and disruption of the responsible genes has shown a lethal phenotype for
Escherichia coli
. In the MEP pathway, 4-diphosphocytidyl-2-
C
-methyl-
d
-erythritol is formed from 2-
C
-methyl-
d
-erythritol 4-phosphate (MEP) and CTP in a reaction catalyzed by a 4-diphosphocytidyl-2-
C
-methyl-
d
-erythritol synthase (IspD). In the present work, we demonstrate that Rv3582c is essential for
M. tuberculosis
: Rv3582c has been cloned and expressed, and the encoded protein has been purified. The purified
M. tuberculosis
IspD protein was capable of catalyzing the formation of 4-diphosphocytidyl-2-
C
-methyl-
d
-erythritol in the presence of MEP and CTP. The enzyme was active over a broad pH range (pH 6.0 to 9.0), with peak activity at pH 8.0. The activity was absolutely dependent upon divalent cations, with 20 mM Mg
2+
being optimal, and replacement of CTP with other nucleotide 5′-triphosphates did not support activity. Under the conditions tested,
M. tuberculosis
IspD had
K
m
values of 58.5 μM for MEP and 53.2 μM for CTP. Calculated
k
cat
and
k
cat
/
K
m
values were 0.72 min
−1
and 12.3 mM
−1
min
−1
for MEP and 1.0 min
−1
and 18.8 mM
−1
min
−1
for CTP, respectively.
摘要
结核分枝杆菌
结核分枝杆菌利用赤藓醇磷酸甲酯(MEP)途径进行二磷酸异戊烯酯及其异构体二磷酸二甲烯丙酯(所有异戊烯化合物的前体)的生物合成。这一途径是新药靶点的重要来源,因为人类不存在这一途径,而破坏相关基因会导致大肠杆菌出现致死表型。
大肠杆菌
.在 MEP 途径中,4-二磷酸胞嘧啶-2-C
C
-甲基-
d
-赤藓醇由 2-
C
-甲基-
d
-4-磷酸赤藓醇(MEP)和CTP在4-二磷酸-2-
C
-甲基-
d
-赤藓糖醇合成酶(IspD)催化的反应。在本研究中,我们证明了 Rv3582c 对结核杆菌的生长至关重要。
结核杆菌
Rv3582c:Rv3582c 已被克隆和表达,其编码蛋白已被纯化。纯化的
结核杆菌
IspD 蛋白能够催化形成 4-二磷酸胞嘧啶-2-C
C
-甲基-
d
-赤藓醇。该酶在广泛的 pH 值范围(pH 值 6.0 至 9.0)内都具有活性,在 pH 值 8.0 时活性达到峰值。该酶的活性完全依赖于二价阳离子,20 mM Mg
2+
用其他核苷酸 5′-三磷酸酯代替 CTP 并不支持其活性。在测试条件下
结核杆菌
IspD 具有
K
m
为 58.5 μM,CTP 为 53.2 μM。计算得出
k
cat
和
k
cat
/
K
m
值为 0.72 min
-1
和 12.3 毫摩尔
-1
分钟
-1
和 12.3 毫摩尔
-1
和 18.8 毫摩尔
-1
分钟
-1
和 18.8 mM -1 min -1。