ROLE OF PEPTIDE CONFORMATION IN THE RATE AND MECHANISM OF DEAMIDATION OF ASPARAGINYL RESIDUES
ROLE OF PEPTIDE CONFORMATION IN THE RATE AND MECHANISM OF DEAMIDATION OF ASPARAGINYL RESIDUES
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DOI：
10.1021/bi00420a015
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发表时间：
1988-10-04
期刊：
影响因子：
2.9
通讯作者：
SCHIRCH, V
中科院分区：
文献类型：
--
作者：
LURA, R;SCHIRCH, V
四肽Val-Asn-Gly-Ala和N-乙酰基-Val-Asn-Gly-Ala在pH 7.0下以相似的速率经历天冬酰胺基残基的脱酰胺化。它们是不同的产品。N-乙酰基肽分别产生3：1比例的N-乙酰基-Val-iosAsp-Gly-Ala和N-乙酰基-Val-Asp-Gly-Ala。非乙酰化的肽没有检测到这些产物的量，而是给出了由天冬酰胺基侧链酰胺被缬氨酸的氨基末端亲核置换形成的环状肽。该化合物在天冬酰胺酰基残基的碳2处缓慢转化。在高于7.5的pH值下，非乙酰化肽也经历脱酰胺以形成比例为3：1的Val-isoAsp-Gly-Ala和Val-Asp-gly-Ala。质子NMR谱的乙酰化和nonacetylated四肽表明，低于pH值7.5，他们有非常不同的首选构象，正是这些不同的构象，导致不同的脱酰胺的机制。在pH 9.0以上，两种肽具有相似的构象，并通过相同的机制脱酰胺，得到等效的产物。两种脱酰胺机制均不受缓冲液的一般碱催化作用的影响。这些结果表明，蛋白质中天冬酰胺基-甘氨酰序列的脱酰胺速率将根据每种相应蛋白质的肽骨架的构象而变化。结果还表明，氨基末端倒数第二个天冬酰胺残基可以反应形成N-末端封闭的七元环。
The tetrapeptides Val-Asn-Gly-Ala and N-acetyl-Val-Asn-Gly-Ala undergo deamidation of the asparaginyl residue at pH 7.0 at similar rates. However, they form different products. The N-acetyl peptide gave a 3:1 ratio of N-acetyl-Val-iosAsp-Gly-Ala and N-acetyl-Val-Asp-Gly-Ala, respectively. The nonacetylated peptide gave no detectable amounts of these products but rather gave a cyclic peptide formed from the nucleophilic displacement of the asparaginyl side chain amide by the amino terminus of valine. This compound was slowly inverted at carbon 2 of the asparaginyl residue. At pH values above 7.5, the nonacetylated peptide also underwent deamidation to form Val-isoAsp-Gly-Ala and Val-Asp-gly-Ala in the 3:1 ratio. Proton NMR spectra of the acetylated and nonacetylated tetrapeptides show that below pH 7.5 they have very different preferred conformations, and it is these different conformations which result in the different mechanisms of deamidation. Above pH 9.0, both peptides have similar conformations and deamidate by the same mechanism to give equivalent products. Neither mechanism of deamidation was subject to general base catalysis by the buffer. These results suggest that deamidation rates of the asparaginyl-glycyl sequence in proteins will vary according to the conformation of the peptide backbone of each respective protein. The results also show that asparaginyl residues which are penultimate to the amino terminus can react to form an N-terminal-blocked seven-membered ring.