Expeditious, potentially primordial, aminoacylation of nucleotides
Expeditious, potentially primordial, aminoacylation of nucleotides
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DOI：
10.1002/anie.200501591
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发表时间：
2005-01-01
影响因子：
16.6
通讯作者：
Sutherland, JD
中科院分区：
文献类型：
--
作者：
Biron, JP;Parkes, LL;Sutherland, JD
在现代生物化学中，酶法合成的活化的氨基酰tRNA酯(AA-tRNA)作为核糖体合成编码肽的底物[1]，一个主要的目标是了解这一过程产生的进化路径。作为实现这一目标的第一步，我们一直在寻找一种在生物前看似可行的方法，用于核糖核苷酸2о-/3о-羟基的氨酰化。已经报道了一些简单的，潜在的益生素，激活的氨基酸衍生物，最著名的是N-羧酸酐(NCA)。[2]最近发现它们可以通过简单的火山气体羰基硫化物的作用从氨基酸中产生，从而加强了NCA在益生进化中的理由。[3]因此，我们决定研究NCA对核苷酸的氨基酰化作用。起初，我们担心腺嘌呤和胞嘧啶的碱基氨基比2о-/3о-羟基更具亲核性；然而，最近的发现表明，NCA与无机磷酸反应生成氨基酰基磷酸酯。[4]这表明，通过磷酸单酯的初始氨酰化反应，然后分子内氨酰基转移，可能生成核苷酸氨基酰基酯。通过中间体羧基磷酸酸酐进行的核苷酸氨酰化反应类似于氨基酰基-tRNA合成酶(AA-RS)的化学。这些酶通过氨基酸羧酸盐对о的亲核攻击产生5о-氨基酰基腺苷(5ATPAA-AMP)1(A=腺嘌呤)。然后，AA-RS催化同源tRNA1到2о/3о-末端的分子间氨酰转移，得到腺苷-5о-一磷酸(5о-AMP)(2)和3о-和2о-aatRNA3和4的平衡混合物(方案1)。当从AA-RS的保护环境中分离出来时，5о-AA-AMP高度不稳定，并在水溶液中进行水解和异构化。[5，6]异构化涉及到缓慢的初始分子内氨酰转移，通过八元过渡状态从5о-磷酸到3о-羟基，5，5，然后，后者与2о氨基酸酯快速平衡。如果由5-о-AMP2与NCA反应生成5-о-AA-AMP1是可能的，那么这种分子内转移有望导致寻求的氨基酸酯的形成。我们首先研究了一个简单的模型磷酸单酯与NCA的氨酰化反应是否可能。我们选择磷酸甲酯6作为模型磷酸单酯和Valyl衍生物7，以便与以前关于无机磷酸盐的工作[4]进行比较，因为7易于制备和存储(方案2)。[7]在一般意义上，当磷酸盐处于双离子状态时，当pH值高于7时，磷酸单酯与任何电泳剂的反应更快，(单阴离子状态的pKA为6-7(支持信息))；然而，在高pH值下，NCA的水解/聚合也是有利的。
In contemporary biochemistry, enzymatically synthesized, activated aminoacyl-tRNA esters (aa-tRNA) serve as substrates for coded peptide synthesis by ribosomes,[1] and a major goal is to understand the evolutionary path through which this process arose. As a first step towards this goal, we have been looking to find a prebiotically plausible means for the aminoacylation of ribonucleotide 2о-/3о-hydroxy groups. A number of simple, potentially prebiotic, activated amino acid derivatives have been reported, most notably N-carboxyanhydrides (NCAs).[2] The case for NCAs in prebiotic evolution has recently been strengthened by the finding that they can be produced from amino acids through the action of the simple volcanic gas carbonyl sulfide.[3] We therefore decided to investigate the aminoacylation of nucleotides by NCAs. Initially we were concerned that the nucleobase amino groups of adenine and cytosine would prove more nucleophilic than the 2о-/3о-hydroxy groups; however, recent findings show that NCAs react with inorganic phosphate to give aminoacyl phosphates.[4] This suggests that it might be possible to generate nucleotide aminoacyl esters by initial aminoacylation of the phosphate monoester, followed by intramolecular aminoacyl transfer. Nucleotide aminoacylation by way of intermediate carboxylic phosphoric anhydrides would be analogous to the chemistry of aminoacyl-tRNA synthetase (aa-RS) enzymes. These enzymes generate 5о-aminoacyladenylates (5о-aa-AMP) 1 (A= adenine) through an initial nucleophilic attack of an amino acid carboxylate on ATP. The aa-RS then catalyzes the intermolecular aminoacyl transfer from 1 to the 2о/3о-terminus of a cognate tRNA to give adenosine-5о-monophosphate (5о-AMP)(2) and an equilibrating mixture of 3о-and 2о-aatRNAs 3 and 4 (Scheme 1).When separated from the protective environment of an aa-RS, 5о-aa-AMPs are highly unstable and undergo hydrolysis and isomerization in aqueous solution.[5, 6] The isomerization involves a slow initial intramolecular aminoacyl transfer from the 5о-phosphate to the 3о-hydroxy group via an eight-membered transition state to give the 3о-aminoacyl ester 5, followed by rapid equilibration of the latter with a 2оaminoacyl ester. If it were possible to generate 5о-aa-AMP 1 from 5о-AMP 2 by reaction with an NCA, then this intramolecular transfer would hopefully result in the sought-after formation of aminoacyl esters. We first investigated whether the aminoacylation of a simple model phosphate monoester with an NCA was possible. We chose methyl phosphate 6 as the model phosphate monoester and the valyl derivative 7 to allow comparison with the previous work on inorganic phosphate [4] and because 7 can be easily prepared and stored (Scheme 2).[7] In a general sense, the reaction of a phosphate monoester with any electrophile is faster at pH values above 7 when the phosphate is in its dianionic state,(pKa for the monoanionic state 6–7 (Supporting Information)); however, NCA hydrolysis/polymerization is also favored at high pH values.