Nik1 orthologs or group III hybrid histidine kinases (HHK3) represent a unique cytoplasmic osmosensor that act upstream of HOG/p38 MAPK pathway in fungi. It is an important molecular target for developing new antifungal agents against human pathogens. HHK3 orthologs contain a linear array of alternative HAMP and HAMP-like linker domains (poly-HAMP) in the N-terminal region. HAMP domains are quite common in prokaryotic histidine kinases where it mostly functions as signal transducer mediating conformational changes in the kinase domains. In contrast, poly-HAMP in HHK3 acts as a sensor and signal transducer to regulate histidine kinase activity. However, the mechanistic detail of this is poorly understood. Interestingly, recent studies indicate that the poly-HAMP-mediated regulation of the kinase activity varies among the orthologs. Hik1 is an important HHK3 ortholog from fungus Magnaporthe oryzae. In this paper, we aimed to decipher the role HAMP and HAMP-like linker domains in regulating the activity of Hik1p. We show that Hik1p acts as a bona fide osmosensor and negatively regulates the downstream HOG/p38 MAPK pathway in Saccharomyces cerevisiae. Our data suggest a differential role of the HAMP domains in the functionality of Hik1p. Most interestingly, the deletion of individual domains in poly-HAMP resulted in distinct active forms of Hik1p and thereby indicating that the poly-HAMP domain, instead of acting as on–off switch, regulates the histidine kinase activity by transition through multiple conformational states.

Nik1 直向同源物或 III 组杂合组氨酸激酶 (HHK3) 代表一种独特的细胞质渗透传感器，其作用于真菌中 HOG/p38 MAPK 通路的上游。它是开发针对人类病原体的新型抗真菌剂的重要分子靶标。HHK3 orthologs 在 N 端区域包含一个线性阵列的替代 HAMP 和 HAMP 样接头域（poly-HAMP）。HAMP 结构域在原核组氨酸激酶中非常常见，其中它主要用作介导激酶结构域中构象变化的信号转导器。相比之下，HHK3 中的聚 HAMP 作为传感器和信号转换器来调节组氨酸激酶活性。然而，对此的机械细节知之甚少。有趣的是，最近的研究表明，poly-HAMP 介导的激酶活性调节在直向同源物中有所不同。稻瘟病菌。在本文中，我们旨在破译 HAMP 和 HAMP 样连接域在调节 Hik1p 活性中的作用。我们表明 Hik1p 充当真正的渗透传感器，并对酿酒酵母中的下游 HOG/p38 MAPK 通路进行负调节。我们的数据表明 HAMP 域在 Hik1p 的功能中的不同作用。最有趣的是，poly-HAMP 中单个结构域的缺失导致 Hik1p 的不同活性形式，从而表明 poly-HAMP 结构域不是作为开关，而是通过多种构象状态的转换来调节组氨酸激酶活性。