Deamidation, isomerization, and racemization at asparaginyl and aspartyl residues in peptides. Succinimide-linked reactions that contribute to protein degradation.
Deamidation, isomerization, and racemization at asparaginyl and aspartyl residues in peptides. Succinimide-linked reactions that contribute to protein degradation.
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DOI：
10.1016/s0021-9258(19)75855-4
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发表时间：
1987-01
期刊：
影响因子：
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通讯作者：
T. Geiger;S. Clarke
中科院分区：
文献类型：
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作者：
T. Geiger;S. Clarke
在合成肽中研究了天冬氨酰和天冬酰胺酰脱酰胺、异构化和外消旋化反应，以模拟这些改变蛋白质结构和功能的自发过程。我们在此表明，肽L-Val-L-Tyr-L-Pro-L-Asn-Gly-L-Ala在37 ℃，pH 7.4下经历快速脱酰胺反应，半衰期仅为1.4天，得到琥珀酰琥珀酰亚胺产物。在这些条件下，琥珀酰亚胺产物可以通过水解（半衰期，2.3小时）和通过外消旋化（半衰期，19.5小时）进一步反应。脱酰胺反应的净产物是L-和D-正戊酰基和β-转肽（异戊酰基）六肽的混合物。用天冬氨酸残基取代天冬酰胺残基导致琥珀酰亚胺形成速率降低34倍。发现脱酰胺和异构化反应伴随着显著的外消旋化，其中大部分可以通过琥珀酰亚胺中间体的快速外消旋化来解释。用大的亮氨酰或脯氨酰残基取代含天冬酰胺的肽中的甘氨酰残基导致降解速率降低33-50倍。当孵育这些含Asn-Leu和Asn-Pro的肽时，观察到肽裂解产物。我们的研究表明，天冬氨酸和天冬酰胺残基可能是蛋白质非酶降解的热点，特别是在红细胞和眼透镜等细胞中，这些大分子必须分别发挥约120天和80年的作用。
Aspartyl and asparaginyl deamidation, isomerization, and racemization reactions have been studied in synthetic peptides to model these spontaneous processes that alter protein structure and function. We show here that the peptide L-Val-L-Tyr-L-Pro-L-Asn-Gly-L-Ala undergoes a rapid deamidation reaction with a half-life of only 1.4 days at 37 degrees C, pH 7.4, to give an aspartyl succinimide product. Under these conditions, the succinimide product can further react by hydrolysis (half-time, 2.3h) and by racemization (half-time, 19.5 h). The net product of the deamidation reaction is a mixture of L- and D-normal aspartyl and beta-transpeptidation (isoaspartyl) hexapeptides. Replacement of the asparagine residue by an aspartic acid residue results in a 34-fold decrease in the rate of succinimide formation. Significant racemization was found to accompany the deamidation and isomerization reactions, and most of this could be accounted for by the rapid racemization of the succinimide intermediate. Replacement of the glycyl residue in the asparagine-containing peptide with a bulky leucyl or prolyl residue results in a 33-50-fold decrease in the rate of degradation. Peptide cleavage products are observed when these Asn-Leu and Asn-Pro-containing peptides are incubated. Our studies indicate that both aspartic acid and asparagine residues may be hot spots for the nonenzymatic degradation of proteins, especially in cells such as erythrocytes and eye lens, where these macromolecules must function for periods of about 120 days and 80 years, respectively.