Departamento de Bioquímica, Instituto Nacional de Cardiología Ignacio Chávez, Tlalpan, México DF, 14080, México.
Mol Microbiol. 2011 Nov;82(3):578-90. doi: 10.1111/j.1365-2958.2011.07832.x. Epub 2011 Sep 29.
In Saccharomyces cerevisiae, the first committed step in the lysine (Lys) biosynthetic pathway is catalysed by the Lys20 and Lys21 homocitrate synthase (HCS) isoforms. Overexpression of Lys20 resulted in eightfold increased Lys, as well as 2-oxoglutarate pools, which were not attained by overexpressing Lys21 or other pathway enzymes (Lys1, Lys9 or Lys12). A metabolic control analysis-based strategy, by gradually and individually manipulating the Lys20 and Lys21 activities demonstrated that the cooperative and strongly feedback-inhibited Lys21 isoform exerted low control of the pathway flux whereas most of the control resided on the non-cooperative and weakly feedback-inhibited Lys20 isoform. Therefore, the higher control of Lys20 over the Lys flux represents an exception to the dogma of higher pathway control by the strongest feedback-inhibited enzyme and points out to multi-site engineering (HCS isoforms and supply of precursors) to increase Lys synthesis.
在酿酒酵母中，赖氨酸（Lys）生物合成途径中的第一个关键步骤是由 Lys20 和 Lys21 同型柠檬酸合酶（HCS）同工酶催化的。Lys20 的过表达导致 Lys 和 2-氧戊二酸池增加了八倍，而过表达 Lys21 或其他途径的酶（Lys1、Lys9 或 Lys12）则无法达到这一效果。通过逐步和单独操纵 Lys20 和 Lys21 的活性进行代谢控制分析的策略表明，协同且受强反馈抑制的 Lys21 同工酶对途径通量的控制作用较低，而大部分控制作用则取决于非协同且弱反馈抑制的 Lys20 同工酶。因此，Lys20 对 Lys 通量的更高控制代表了由最强反馈抑制酶控制更高途径通量的教条的例外，并指出了多部位工程（HCS 同工酶和前体供应）以增加 Lys 合成。
