Phosphonate natural products possess a range of biological activities as a consequence of their ability to mimic phosphate esters or tetrahedral intermediates formed in enzymatic reactions involved in carboxyl group metabolism. The dianionic form of these compounds at pH 7 poses a drawback with respect to their ability to mimic carboxylates and tetrahedral intermediates. Microorganisms producing phosphonates have evolved two solutions to overcome this hurdle: biosynthesis of monoanionic phosphinates containing two P-C bonds or esterification of the phosphonate group. The latter solution was first discovered for the antibiotic dehydrophos that contains a methyl ester of a phosphonodehydroalanine group. We report here the expression, purification, substrate scope, and structure of the
O
-methyltransferase from the dehydrophos biosynthetic gene cluster. The enzyme utilizes
S
-adenosylmethionine to methylate a variety of phosphonates including 1-hydroxyethylphosphonate, 1,2-dihydroxyethylphosphonate, and acetyl-1-aminoethylphosphonate. Kinetic analysis showed that the best substrates are tripeptides containing as C-terminal residue a phosphonate analog of alanine suggesting the enzyme acts late in the biosynthesis of dehydrophos. These conclusions are corroborated by the X-ray structure that reveals an active site that can accommodate a tripeptide substrate. Furthermore, the structural studies demonstrate a conformational change brought about by substrate or product binding. Interestingly, the enzyme has low substrate specificity and was used to methylate the clinical antibiotic fosfomycin and the antimalaria clinical candidate fosmidomycin, showing its promise for applications in bioengineering.
膦酸天然产物具有一系列生物活性,这是因为它们能够模拟在羧基代谢中涉及的酶反应中形成的磷酸酯或四面体中间体。这些化合物在pH 7下的二阴离子形式对于模拟羧酸和四面体中间体的能力存在缺陷。产生膦酸的微生物已经演化出两种解决方案来克服这个障碍:合成含有两个P-C键的单阴离子膦酸盐或对膦酸基团进行酯化。后一种解决方案首次发现于含有膦酸脱氢丙氨酸甲酯基团的抗生素脱氢膦。我们在这里报道了脱氢膦生物合成基因簇中的O-甲基转移酶的表达、纯化、底物范围和结构。该酶利用S-腺苷甲硫氨酸对多种膦酸进行甲基化,包括1-羟乙基膦酸、1,2-二羟乙基膦酸和乙酰-1-氨基乙基膦酸。动力学分析表明,最佳底物是三肽,其C-末端残基是丙氨酸的膦酸类似物,这表明该酶在脱氢膦的生物合成过程中起到晚期作用。这些结论得到了X射线结构的证实,揭示了一个可以容纳三肽底物的活性位点。此外,结构研究表明,底物或产物结合引起了构象变化。有趣的是,该酶的底物特异性较低,并且已被用于甲基化临床抗生素磷霉素和抗疟疾临床候选药物磷膜多霉素,显示了其在生物工程应用中的潜力。