嗜盐细菌中四氢嘧啶和羟基四氢嘧啶的生物合成及其生物学功能

Ectoine and hydroxyectoine: biosynthesis and its biological function in halophilic bacteria

摘要:

在嗜盐细菌盐适应中，四氢嘧啶（1，4，5，6-四氢-2-甲基-4-嘧啶羧酸）和羟基四氢嘧啶（1，4，5，6-四氢-2-甲基-5-羟基-4-嘧啶羧酸）发挥着十分重要的作用。四氢嘧啶的生物合成以L-天冬氨酸-β-半醛（ASA）为底物，依次由2，4-二氨基丁酸转氨酶（EctB），2，4-二氨基丁酸乙酰基转移酶（EctA）和四氢嘧啶合成酶（EctC）催化反应，分别生成L-2，4-二氨基丁酸（DABA），N-乙酰-L-2，4-二氨基丁酸（ADABA）和四氢嘧啶。羟基四氢嘧啶则由四氢嘧啶羟化酶（EctD）将四氢嘧啶羟基化产生。通常，四氢嘧啶合成基因以ectABC基因簇的形式存在，而羟基四氢嘧啶合成基因ectD单独存在。四氢嘧啶生物合成基因在微生物菌株和转基因经济作物中的表达可以提高其耐盐碱旱等抗逆能力，羟基四氢嘧啶合成基因的表达可以增强宿主耐热和耐干燥的能力。四氢嘧啶类相容性溶质的生物学功能及其潜在应用已成为前沿性研究热点。

Abstract:

Ectoine[(S)-2-methyl-1,4,5,6-tetrahydropyrimidine-4-carboxylic acid] and its hydroxyectoine[(S,S)-2-methyl-5-hydroxy-1,4,5,6-tetrahydropyrimidine-4-carboxylic acid] play a crucial role in the salt adaptation mechanism in halophilic bacteria. The biosynthesis of ectoine is catalyzed by three enzymes:L-diaminobutyric acid aminotransferase (EctB), L-diaminobutyric acid acetyltransferase (EctA), and ectoine synthase (EctC). Using L-Aspartate-β-semialdehyde (ASA) as the substrate, L-2,4-diaminobutyrate (DABA), N-γ-Acetyl-L-2,4-diaminobutyrate (ADABA) and ectoine are biosynthesized successively. Hydroxyectoine is produced by the hydroxylation of ectoine with ectoine hydroxylase (EctD). In normal, the ectoine synthesis genes exist in the form of ectABC gene cluster, while the hydroxyectoine synthesis gene ectD exists alone. The functional expression of ectoine synthesis genes in microbe and genetically modified cash crops can improve their resistance to extreme conditions such as hyperosmotic stress, alkali stress, and drought. The expression of hydroxyectoine synthesis gene also can enhance the host's ability to resist heat and drought. The biological functions and potential applications of ectoines have become a frontier hotspot.