Nyyssola A, Kerovuo J, Kaukinen P, von Weymarn N, Reinikainen T
Danisco Cultor Innovation, Kantvik, Sokeritehtaantie 20, FIN-02460 Kantvik, Finland.
J Biol Chem. 2000 Jul 21;275(29):22196-201. doi: 10.1074/jbc.M910111199.
Glycine betaine is a compatible solute, which is able to restore and maintain osmotic balance of living cells. It is synthesized and accumulated in response to abiotic stress. Betaine acts also as a methyl group donor and has a number of important applications including its use as a feed additive. The known biosynthetic pathways of betaine are universal and very well characterized. A number of enzymes catalyzing the two-step oxidation of choline to betaine have been isolated. In this work we have studied a novel betaine biosynthetic pathway in two phylogenically distant extreme halophiles, Actinopolyspora halophila and Ectothiorhodospira halochloris. We have identified a three-step series of methylation reactions from glycine to betaine, which is catalyzed by two methyltransferases, glycine sarcosine methyltransferase and sarcosine dimethylglycine methyltransferase, with partially overlapping substrate specificity. The methyltransferases from the two organisms show high sequence homology. E. halochloris methyltransferase genes were successfully expressed in Escherichia coli, and betaine accumulation and improved salt tolerance were demonstrated.
甘氨酸甜菜碱是一种相容性溶质，能够恢复和维持活细胞的渗透平衡。它是在非生物胁迫下合成并积累的。甜菜碱还可作为甲基供体，有许多重要应用，包括用作饲料添加剂。已知的甜菜碱生物合成途径是通用的且已得到很好的表征。已分离出多种催化胆碱两步氧化生成甜菜碱的酶。在这项工作中，我们研究了两种系统发育关系较远的极端嗜盐菌——嗜盐放线多孢菌和嗜盐嗜盐外硫红螺菌中的一种新型甜菜碱生物合成途径。我们确定了从甘氨酸到甜菜碱的三步甲基化反应系列，该反应由两种甲基转移酶催化，即甘氨酸 - 肌氨酸甲基转移酶和肌氨酸 - 二甲基甘氨酸甲基转移酶，它们的底物特异性部分重叠。这两种生物的甲基转移酶显示出高度的序列同源性。嗜盐嗜盐外硫红螺菌甲基转移酶基因在大肠杆菌中成功表达，并证明了甜菜碱的积累和耐盐性的提高。
