Cyclic peptides are promising compounds for new chemical biological tools and therapeutics due to their structural diversity, resistance to proteases, and membrane permeability. Amatoxins, the toxic principles of poisonous mushrooms, are biosynthesized on ribosomes as 35mer precursor peptides, which are ultimately converted to hydroxylated bicyclic octapeptides. The initial cyclization steps, catalyzed by a dedicated prolyl oligopeptidase (POPB), involves removal of the 10-amino acid leader sequence from the precursor peptide and transpeptidation to produce a monocyclic octapeptide intermediate. The utility of POPB as a general catalyst for peptide cyclization was systematically characterized using a range of precursor peptide substrates produced either in E. coli or chemically. Substrates produced in E. coli were expressed either individually or in mixtures produced by codon mutagenesis. A total of 127 novel peptide substrates were tested, of which POPB could cyclize 100. Peptides of 7–16 residues were cyclized at least partially. Synthetic 25mer precursor peptide substrates containing modified amino acids including d-Ala, β-Ala, N-methyl-Ala, and 4-hydroxy-Pro were also successfully cyclized. Although a phalloidin heptapeptide with all L amino acids was not cyclized, partial cyclization was seen when l-Thr at position #5 was replaced with the naturally occurring D amino acid. POPB should have broad applicability as a general catalyst for macrocyclization of peptides containing 7 to at least 16 amino acids, with an optimum of 8–9 residues.

中文翻译：

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脯氨酰寡肽酶B在多肽大环化中的多功能性

环状肽由于其结构多样性，对蛋白酶的抗性和膜通透性，是用于新型化学生物学工具和治疗剂的有前途的化合物。Amatoxins是有毒蘑菇的毒性原理，是在核糖体上以35mer前体肽的形式生物合成的，最终被转化为羟基化的双环八肽。最初的环化步骤由专用的脯氨酰寡肽酶（POPB）催化，涉及从前体肽中除去10个氨基酸的前导序列并进行转肽作用以产生单环八肽中间体。使用在大肠杆菌或化学方法中产生的一系列前体肽底物，系统地表征了POPB作为肽环化通用催化剂的效用。基板生产于大肠杆菌可以单独表达，也可以通过密码子诱变产生的混合物表达。总共测试了127种新的肽底物，其中POPB可以环化100个。7–16个残基的肽至少部分地被环化。含有修饰氨基酸（包括d -Ala，β-Ala，N-甲基-Ala和4-hydroxy-Pro）的合成25mer前体肽底物也已成功环化。尽管具有全部L个氨基酸的鬼笔环肽七肽没有被环化，但是当＃5位的1- Thr被天然存在的D氨基酸替换时，看到了部分环化。POPB应当具有广泛的适用性，可以作为含有7至至少16个氨基酸，最佳8-9个残基的肽大环化的一般催化剂。