Single-chain variable fragments (scFvs), composed of variable domains of heavy and light chains of an antibody joined by a linker, share antigen binding capacity with their parental antibody. Due to intrinsically low solubility and stability, only two Escherichia coli-produced scFvs have been approved for therapy. Here we report that a 33-residue peptide, termed P17 tag, increases the solubility of multiple scFvs produced in Escherichia coli SHuffle strain by up to 11.6 fold. Hydrophilic sequence, especially charged residues, but not the predicted α-helical secondary structure of P17 tag, contribute to the solubility enhancement. Notably, the P17 tag elevates the thermostability of scFv as efficiently as intra-domain disulfide bonds. Moreover, a P17-tagged scFv targeting hepatitis B virus surface proteins shows over two-fold higher antigen-binding affinity and virus-neutralizing activity than the untagged version. These data strongly suggest a type I intramolecular chaperone-like activity of the P17 tag. Hence, the P17 tag could benefit the research, production, and application of scFv.

单链可变片段 (scFvs) 由通过接头连接的抗体重链和轻链的可变结构域组成，与其亲本抗体共享抗原结合能力。由于固有的低溶解度和稳定性，只有两种大肠杆菌产生的 scFv 已被批准用于治疗。在这里，我们报告了一种名为 P17 标签的 33 个残基肽增加了大肠杆菌中产生的多个 scFv 的溶解度随机应变高达 11.6 倍。亲水序列，尤其是带电残基，而不是预测的 P17 标签的 α-螺旋二级结构，有助于提高溶解度。值得注意的是，P17 标签提高 scFv 的热稳定性与域内二硫键一样有效。此外，靶向乙型肝炎病毒表面蛋白的 P17 标记的 scFv 显示出比未标记版本高两倍以上的抗原结合亲和力和病毒中和活​​性。这些数据强烈表明P17标签的I型分子内伴侣样活性。因此，P17标签有利于scFv的研究、生产和应用。