Capsule polysaccharide is a major virulence factor of Klebsiella pneumoniae, a nosocomial pathogen associated with a wide range of infections. It protects bacteria from harsh environmental conditions, immune system response, and phage infection. To access cell wall-located receptors, some phages possess tailspike depolymerases that degrade the capsular polysaccharide. Here, we present the crystal structure of a tailspike against Klebsiella, KP32gp38, whose primary sequence shares no similarity to other proteins of known structure. In the trimeric structure of KP32gp38, each chain contains a flexible N-terminal domain, a right-handed parallel β helix domain and two β sandwiches with carbohydrate binding features. The crystal structure and activity assays allowed us to locate the catalytic site. Also, our data provide experimental evidence of a branching architecture of depolymerases in KP32 Klebsiella viruses, as KP32gp38 displays nanomolar affinity to another depolymerase from the same phage, KP32gp37. Results provide a structural framework for enzyme engineering to produce serotype-broad-active enzyme complexes against K. pneumoniae.

胶囊多糖是肺炎克雷伯菌的主要致病因子，肺炎克雷伯菌是与多种感染相关的医院病原体。它可以保护细菌免受恶劣的环境条件，免疫系统反应和噬菌体感染的侵害。为了接近细胞壁定位的受体，一些噬菌体具有降​​解荚膜多糖的尾钉解聚酶。在这里，我们介绍了针对克雷伯氏菌的尾钉的晶体结构，KP32gp38，其一级序列与已知结构的其他蛋白质没有相似性。在KP32gp38的三聚体结构中，每条链均包含一个灵活的N末端结构域，一个右旋平行β螺旋结构域和两个具有碳水化合物结合特征的β三明治。晶体结构和活性测定使我们能够定位催化位点。同样，我们的数据提供了KP32克雷伯氏菌病毒中解聚酶分支结构的实验证据，因为KP32gp38对同一噬菌体KP32gp37的另一种解聚酶表现出纳摩尔亲和力。结果为酶工程生产抗肺炎克雷伯菌的血清型广谱活性酶复合物提供了结构框架。