Archaea have been shown to produce isoprenoids from mevalonate; however, genome analysis has failed to identify several genes in the mevalonate pathway on the basis of sequence similarity. A predicted archaeal kinase, coded for by the MJ0044 gene, was associated with other mevalonate pathway genes in the archaea and was predicted to be the “missing” phosphomevalonate kinase. The MJ0044-derived protein was tested for phosphomevalonate kinase activity and was found not to catalyze this reaction. The MJ0044 gene product was found to phosphorylate isopentenyl phosphate, generating isopentenyl diphosphate. Unlike other known kinases associated with isoprene biosynthesis,
Extreme acidophiles are capable of growth at pH values near zero. Sustaining life in acidic environments requires extensive adaptations of membranes, proton pumps, and DNA repair mechanisms. Here we describe an adaptation of a core biochemical pathway, the mevalonate pathway, in extreme acidophiles. Two previously known mevalonate pathways involve ATP dependent decarboxylation of either mevalonate 5-phosphate or mevalonate 5-pyrophosphate, in which a single enzyme carries out two essential steps: (1) phosphorylation of the mevalonate moiety at the 3-OH position and (2) subsequent decarboxylation. We now demonstrate that in extreme acidophiles, decarboxylation is carried out by two separate steps: previously identified enzymes generate mevalonate 3,5-bisphosphate and a new decarboxylase we describe here, mevalonate 3,5-bisphosphate decarboxylase, produces isopentenyl phosphate. Why use two enzymes in acidophiles when one enzyme provides both functionalities in all other organisms examined to date? We find that at low pH, the dual function enzyme, mevalonate 5-phosphate decarboxylase is unable to carry out the first phosphorylation step, yet retains its ability to perform decarboxylation. We therefore propose that extreme acidophiles had to replace the dual-purpose enzyme with two specialized enzymes to efficiently produce isoprenoids in extremely acidic environments.
极端酸性菌可以在接近零的pH值下生长。在酸性环境中维持生命需要膜、质子泵和DNA修复机制的广泛适应。在这里,我们描述了极端酸性菌中一个核心生化途径——甲烷基丙酮酸途径的适应性。先前已知的两个甲烷基丙酮酸途径涉及ATP依赖性脱羧化,分别是甲烷基丙酮酸5-磷酸或甲烷基丙酮酸5-焦磷酸,其中单个酶执行两个必要的步骤:(1)在3-OH位置磷酸化甲烷基丙酮基团和(2)随后脱羧化。我们现在证明,在极端酸性菌中,脱羧化是通过两个单独的步骤进行的:先前鉴定的酶生成甲烷基丙酮酸3,5-双磷酸盐,我们在这里描述了一个新的脱羧酶,甲烷基丙酮酸3,5-双磷酸盐脱羧酶,产生异戊烯基磷酸盐。为什么在酸性菌中使用两个酶,而在所有其他已研究的生物中一个酶提供了两种功能?我们发现,在低pH值下,双重功能酶甲烷基丙酮酸5-磷酸脱羧酶无法执行第一步磷酸化反应,但保留其执行脱羧反应的能力。因此,我们建议极端酸性菌必须用两种专门的酶来有效地在极端酸性环境中产生异戊烯类物质,以取代双重用途酶。