Cell penetrating peptides (CPPs) have emerged as powerful tools for delivering bioactive cargoes, such as biosensors or drugs to intact cells. One limitation of CPPs is their rapid degradation by intracellular proteases. β‐hairpin “protectides” have previously been demonstrated to be long‐lived under cytosolic conditions due to their secondary structure. The goal of this work was to demonstrate that arginine‐rich β‐hairpin peptides function as both protectides and as CPPs. Peptides exhibiting a β‐hairpin motif were found to be rapidly internalized into cells with their uptake efficiency dependent on the number of arginine residues in the sequence. Cellular internalization of the β‐hairpin peptides was compared to unstructured, scrambled sequences and to commercially available, arginine‐rich CPPs. The unstructured peptides displayed greater uptake kinetics compared to the structured β‐hairpin sequences; however, intracellular stability studies revealed that the β‐hairpin peptides exhibited superior stability under cytosolic conditions with a 16‐fold increase in peptide half‐life. This study identifies a new class of long‐lived CPPs that can overcome the stability limitations of peptide‐based reporters or bioactive delivery mechanisms in intact cells.

中文翻译：

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CPProtectides：快速摄取折叠良好的β-发夹肽，增强对细胞内降解的抵抗力。

细胞穿透肽（CPP）已经成为将生物活性物质（例如生物传感器或药物）输送到完整细胞的强大工具。CPP的一个局限性是它们被细胞内蛋白酶迅速降解。先前已经证明，β-发夹“保护剂”由于其二级结构而在胞质条件下可以长期存在。这项工作的目的是证明富含精氨酸的β-发夹肽既可作为保护剂，又可作为CPP。发现具有β-发夹基序的肽被迅速内化到细胞中，其吸收效率取决于序列中精氨酸残基的数量。将β-发夹肽的细胞内在化与未结构化，混乱的序列以及可商购的富含精氨酸的CPP进行了比较。与结构化的β-发夹序列相比，非结构化的肽表现出更大的吸收动力学。然而，细胞内稳定性研究表明，β-发夹肽在胞质条件下表现出优异的稳定性，肽半衰期增加了16倍。这项研究确定了一种新型的长寿命CPP，它们可以克服完整细胞中基于肽的报告基因或生物活性传递机制的稳定性限制。