Artificial enzymes with serine, aspartic acid, and histidine that mimic the catalytic triad of serine proteases have been studied. However, they were mainly investigated for their cleavage activity on low molecular-weight esters and amides, and there has been a lack of knowledge about their protein cleavage activity. We previously found that not only ternary polyacrylamides with serine, aspartic acid, and histidine but also homo-polyacrylamides with a single type of amino acid cleaved bovine and human serum albumins. These results suggested that the carboxy group, a common functional group in active polymers, may be involved in the expression of activity. In this study, we synthesized histidine polymers in which the carboxy group was changed to a carboxamido or amino group and investigated the relationships between structure and activity. Histidine homopolymers and histidine-acrylamide copolymers were incubated with bovine serum albumin at 37 °C for one week under different pH conditions and then analyzed by sodium dodecyl-sulfate polyacrylamide gel electrophoresis. In the case of histidine homopolymers, the carboxy-type homopolymers were active under weakly acidic to neutral conditions, while the carboxamido- and amino-type homopolymers were not active regardless of liquid properties. In the case of histidine-acrylamide copolymers, their activity was essentially the same as that of each type of histidine homopolymer, but for all types of copolymers, activity appeared under weakly basic conditions when the histidine monomer units were of a specific density. The carboxy-type copolymers with dual-mode activity showed different degradation patterns of bovine serum albumin under acidic and basic conditions. The structural features common to the active homopolymers and copolymers suggested that the carboxy group contributes to the activity under weakly acidic to neutral conditions, while the imidazole group of the histidine side chain and its density contribute to the activity under weakly basic conditions.

中文翻译：

---

组氨酸侧链聚丙烯酰胺的 pH 依赖性蛋白水解活性

已经研究了模拟丝氨酸蛋白酶催化三联体的含有丝氨酸、天冬氨酸和组氨酸的人工酶。然而，主要研究它们对低分子量酯和酰胺的裂解活性，并且缺乏对其蛋白质裂解活性的了解。我们之前发现不仅具有丝氨酸、天冬氨酸和组氨酸的三元聚丙烯酰胺，而且还具有具有单一类型氨基酸裂解的牛和人血清白蛋白的均聚丙烯酰胺。这些结果表明羧基是活性聚合物中常见的官能团，可能参与活性的表达。在本研究中，我们合成了组氨酸聚合物，其中羧基被改变为羧酰胺基或氨基，并研究了结构和活性之间的关系。将组氨酸均聚物和组氨酸-丙烯酰胺共聚物与牛血清白蛋白在37℃、不同pH条件下孵育1周，然后通过十二烷基硫酸钠聚丙烯酰胺凝胶电泳进行分析。在组氨酸均聚物的情况下，羧基型均聚物在弱酸性至中性条件下具有活性，而甲酰胺基和氨基型均聚物无论液体性质如何都没有活性。就组氨酸-丙烯酰胺共聚物而言，其活性与每种类型的组氨酸均聚物的活性基本相同，但对于所有类型的共聚物，当组氨酸单体单元具有特定密度时，在弱碱性条件下出现活性。具有双模式活性的羧基型共聚物在酸性和碱性条件下表现出不同的牛血清白蛋白降解模式。活性均聚物和共聚物共有的结构特征表明，羧基有助于弱酸性至中性条件下的活性，而组氨酸侧链的咪唑基团及其密度有助于弱碱性条件下的活性。