ABSTRACT
CDP-2,3-di
-O-
geranylgeranyl-
sn
-glycerol:
l
-serine
O
-archaetidyltransferase (archaetidylserine synthase) activity in cell extracts of
Methanothermobacter thermautotrophicus
cells was characterized. The enzyme catalyzed the formation of unsaturated archaetidylserine from CDP-unsaturated archaeol and
l
-serine. The identity of the reaction products was confirmed by thin-layer chromatography, fast atom bombardment-mass spectrum analysis, and chemical degradation. The enzyme showed maximal activity in the presence of 10 mM Mn
2+
and 1% Triton X-100. Among various synthetic substrate analogs, both enantiomers of CDP-unsaturated archaeols with ether-linked geranylgeranyl chains and CDP-saturated archaeol with ether-linked phytanyl chains were similarly active toward the archaetidylserine synthase. The activity on the ester analog of the substrate was two to three times higher than that on the corresponding ether-type substrate. The activity of
d
-serine with the enzyme was 30% of that observed for
l
-serine. A trace amount of an acid-labile, unsaturated archaetidylserine intermediate was detected in the cells by a pulse-labeling experiment. A gene (MT1027) in
M. thermautotrophicus
genome annotated as the gene encoding phosphatidylserine synthase was found to be homologous to
Bacillus subtilis pssA
but not to
Escherichia coli pssA.
The substrate specificity of phosphatidylserine synthase from
B. subtilis
was quite similar to that observed for the
M. thermautotrophicus
archaetidylserine synthase, while the
E. coli
enzyme had a strong preference for CDP-1,2-diacyl-
sn
-glycerol. It was concluded that
M. thermautotrophicus
archaetidylserine synthase belongs to subclass II phosphatidylserine synthase (
B. subtilis
type) on the basis of not only homology but also substrate specificity and some enzymatic properties. The possibility that a gene encoding the subclass II phosphatidylserine synthase might be transferred from a bacterium to an ancestor of methanogens is discussed.
摘要
CDP-2,3-二
-O-
香叶基
甘油
-甘油:
l
-丝氨酸
O
-的细胞提取物中的古乙酰转移酶(古乙酰丝氨酸合成酶)活性。
的活性进行了表征。
的活性进行了表征。该酶催化 CDP-不饱和古醇和 lDP-不饱和古丝氨酸的形成。
l
-丝氨酸。反应产物的特征通过薄层色谱法、快速原子轰击质谱分析和化学降解得到了证实。该酶在 10 mM Mn
2+
和 1% Triton X-100 的条件下,酶的活性达到最高。在各种合成底物类似物中,具有醚键香叶基纯正甘油链的 CDP 不饱和古醇和具有醚键植烷酰链的 CDP 饱和古醇的两种对映体对古乙酰丝氨酸合成酶具有类似的活性。对底物的酯类似物的活性比对相应的醚型底物的活性高 2 到 3 倍。对
d
-丝氨酸合成酶活性的 30%。
l
-的 30%。通过脉冲标记实验,在细胞中检测到了微量的酸性不饱和古乙酰丝氨酸中间体。热自养菌中的一个基因(MT1027)
基因组中的一个基因(MT1027
基因组中被注释为编码磷脂酰丝氨酸合成酶的基因(MT1027)与
枯草芽孢杆菌 pssA
同源,但与
大肠杆菌 pssA 同源。
枯草芽孢杆菌磷脂酰丝氨酸合成酶的底物特异性
底物特异性
的底物特异性十分相似。
M. thermautotrophicus
的底物特异性十分相似,而大肠杆菌的
大肠杆菌
酶对 CDP-1,2-二乙酰基-丝氨酸有强烈的偏好。
甘油
-甘油。结论是
热自养蝠
古乙酰丝氨酸合成酶属于亚类 II 磷脂酰丝氨酸合成酶(B. subclass II phosphatidylserine synthase)。
B. subtilis
型),其依据不仅是同源性,还有底物特异性和一些酶学特性。本文讨论了编码亚类 II 磷脂酰丝氨酸合成酶的基因从细菌转移到甲烷菌祖先的可能性。