The existence of the classical mevalonate (MVA) pathway was examined in the thermoacidophilic archaeon Sulfolobus solfataricus. The pathway is considered uncommon among archaea because the genes of the orthologues of phosphomevalonate kinase (PMK) and/or diphosphomevalonate decarboxylase (DMD) are absent in the genomes of most archaea. Instead, the modified MVA pathway, which involves isopentenyl phosphate kinase (IPK), has been proposed to exist in the archaea that lack the classical pathway. However, some archaea including S. solfataricus possess the genes of the orthologues of both IPK and all enzymes of the classical pathway. Biochemical characterization using recombinant proteins showed that the orthologues of the enzymes catalyzing the late steps of the classical pathway, i.e. MVA kinase, PMK and DMD, are all active. Moreover, in vitro conversion of the intermediates in the classical and modified pathways by cell-free extract from S. solfataricus indicated that only the classical pathway likely works in the organism.
研究人员考察了嗜酸性古菌溶胀
硫杆菌(Sulfolobus solfataricus)中是否存在经典的甲羟
戊酸(MVA)途径。这种途径在古生菌中并不常见,因为大多数古生菌的
基因组中都没有
磷酸甲羟
戊酸激酶(PMK)和/或二
磷酸甲羟
戊酸脱羧酶(
DMD)的同源
基因。相反,有人提出在缺乏经典途径的古细菌中存在改良的 MVA 途径,其中涉及
磷酸异
戊烯酯激酶(IPK)。然而,包括溶菌体在内的一些古菌拥有 IPK 和经典途径所有酶的直向同源物
基因。利用
重组蛋白进行的生化鉴定表明,催化经典途径后期步骤的酶的直向同源物,即 MVA 激酶、PMK 和
DMD 都具有活性。此外,用溶藻菌的无细胞
提取物对经典途径和改良途径的中间产物进行体外转化表明,该
生物体内可能只有经典途径起作用。