Porat Iris, Sieprawska-Lupa Magdalena, Teng Quincy, Bohanon Fredrick J, White Robert H, Whitman William B
Department of Microbiology, University of Georgia, Athens, GA 30602, USA.
Mol Microbiol. 2006 Nov;62(4):1117-31. doi: 10.1111/j.1365-2958.2006.05426.x. Epub 2006 Sep 29.
Methanococcus maripaludis is a strictly anaerobic, methane-producing archaeon and facultative autotroph capable of biosynthesizing all the amino acids and vitamins required for growth. In this work, the novel 6-deoxy-5-ketofructose-1-phosphate (DKFP) pathway for the biosynthesis of aromatic amino acids (AroAAs) and p-aminobenzoic acid (PABA) was demonstrated in M. maripaludis. Moreover, PABA was shown to be derived from an early intermediate in AroAA biosynthesis and not from chorismate. Following metabolic labelling with [U-(13)C]-acetate, the expected enrichments for phenylalanine and arylamine derived from PABA were observed. DKFP pathway activity was reduced following growth with aryl acids, an alternative source of the AroAAs. Lastly, a deletion mutant of aroA', which encodes the first step in the DKFP pathway, required AroAAs and PABA for growth. Complementation of the mutants by an aroA' expression vector restored the wild-type phenotype. In contrast, a deletion of aroB', which encodes the second step in the DKFP pathway, did not require AroAAs or PABA for growth. Presumably, methanococci contain an alternative activity for this step. These results identify the initial reactions of a new pathway for the biosynthesis of PABA in methanococci.
马氏沼球菌是一种严格厌氧、产甲烷的古菌，也是一种兼性自养生物，能够生物合成生长所需的所有氨基酸和维生素。在这项研究中，在马氏沼球菌中证实了用于芳香族氨基酸（AroAAs）和对氨基苯甲酸（PABA）生物合成的新的6-脱氧-5-酮果糖-1-磷酸（DKFP）途径。此外，PABA被证明来源于AroAA生物合成的早期中间体，而非分支酸。在用[U-(13)C]-乙酸进行代谢标记后，观察到了来自PABA的苯丙氨酸和芳胺的预期富集情况。在用芳香酸（AroAAs的另一种来源）培养后，DKFP途径的活性降低。最后，编码DKFP途径第一步的aroA'缺失突变体生长需要AroAAs和PABA。用aroA'表达载体对突变体进行互补可恢复野生型表型。相反，编码DKFP途径第二步的aroB'缺失突变体生长不需要AroAAs或PABA。据推测，甲烷球菌在这一步含有替代活性。这些结果确定了甲烷球菌中PABA生物合成新途径的初始反应。
