Kallikrein 4 (KLK4) is a serine protease that is predominantly expressed in the prostate and is overexpressed in prostate cancer. As such, it has gained attention as an attractive target for prostate cancer therapeutics. Currently, only liganded structures of KLK4 exist in the Protein Data Bank. Until now, inferences about the subtle structural changes in KLK4 upon ligand binding have been made by comparison to other liganded forms, rather than to an apo form. In this study, an inhibitor‐free form of KLK4 was crystallized. The crystals obtained belonged to space group P1, contained four molecules in the asymmetric unit and diffracted to 1.64 Å resolution. Interestingly, a nonstandard rotamer of the specificity‐determining residue Asp189 was observed in all chains. This model will provide a useful unliganded structure for the future structure‐guided design of KLK4 inhibitors.

中文翻译：

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丝氨酸蛋白酶激肽释放酶-4的无抑制剂形式的晶体结构。

激肽释放酶4（KLK4）是一种丝氨酸蛋白酶，主要在前列腺中表达，在前列腺癌中过表达。这样，作为前列腺癌治疗剂的有吸引力的靶标，它已引起注意。当前，蛋白质数据库中仅存在KLK4的配体结构。到目前为止，通过与其他配体形式而非载脂蛋白形式的比较，已经推断出在配体结合后KLK4的细微结构变化。在这项研究中，结晶了无抑制剂形式的KLK4。获得的晶体属于空间群P1，在不对称单元中包含四个分子，衍射至1.64Å分辨率。有趣的是，在所有链中都观察到了非标准的特异性决定残基Asp189的旋转异构体。该模型将为KLK4抑制剂的未来结构指导设计提供有用的非配体结构。