Leptospirosis is the most common zoonotic disease caused by pathogenic Leptospira, which is classified into three groups according to virulence. Its pathogenic and intermediate species contain leucine-rich repeat (LRR) proteins that are rarely expressed in non-pathogenic strains. In this study, we presented the crystal structure of LSS_11580 (rLRR20) from pathogenic L. santarosai serovar Shermani. X-ray diffraction at a resolution of 1.99 Å revealed a horseshoe-shaped structure containing seven α-helices and five β-sheets. Affinity assays indicated that rLRR20 interacts with E-cadherin on the cell surface. Interestingly, its binds to the extracellular (EC) 1 domain in human epithelial (E)-cadherin, which is responsible for binding to another E-cadherin molecule in neighboring cells. Several charged residues on the concave face of LRR20 were predicted to interact with EC1 domain. In the affinity assays, these charged residues were replaced by alanine, and their affinities to E-cadherin were measured. Three vital residues and mutation variants of LRR20, namely D56A, E59A, and E123A, demonstrated significantly reduced affinity to E-cadherin compared with the control. Besides, we also demonstrated that rLRR20 induced the expression of neutrophil gelatinase-associated lipocalin (NGAL) in HK2 cells. The low ability of the three mutation variants to induce NGAL expression further demonstrates this induction. The present findings indicate that LRR20 from pathogenic Leptospira binds to E-cadherin and interacts with its EC1 domain. In addition, its induction of NGAL expression in HK2 cells is associated with acute kidney injury in human.

中文翻译：

---

富含钩端螺旋体亮氨酸重复序列20的晶体结构揭示了一种新型E-钙粘蛋白结合蛋白，可诱导HK2细胞中NGAL表达

钩端螺旋体病是由致病性钩端螺旋体引起的最常见的人畜共患疾病，根据毒力可分为三类。其致病和中间物种包含富含亮氨酸的重复（LRR）蛋白，这种蛋白在非致病性菌株中很少表达。在这项研究中，我们介绍了致病性桑塔罗氏酵母血清型Shermani的LSS_11580（rLRR20）的晶体结构。分辨率为1.99Å的X射线衍射显示，马蹄形结构包含七个α螺旋和五个β折叠。亲和力测定表明，rLRR20与细胞表面的E-cadherin相互作用。有趣的是，它与人上皮（E）-钙粘着蛋白中的细胞外（EC）1结构域结合，后者负责与相邻细胞中的另一个E-钙粘着蛋白分子结合。LRR20的凹面上的几个带电残基预计与EC1域相互作用。在亲和力测定中，这些带电荷的残基被丙氨酸取代，并测量了它们与E-钙粘蛋白的亲和力。与对照相比，LRR20的三个重要残基和突变变体D56A，E59A和E123A表现出对E-钙粘蛋白的亲和力大大降低。此外，我们还证明了rLRR20诱导了HK2细胞中嗜中性粒细胞明胶酶相关脂质运载蛋白（NGAL）的表达。三种突变变体诱导NGAL表达的低能力进一步证明了这种诱导。目前的发现表明，来自致病性钩端螺旋体的LRR20与E-钙粘蛋白结合并与其EC1域相互作用。此外，