Watzer Björn, Spät Philipp, Neumann Niels, Koch Moritz, Sobotka Roman, Macek Boris, Hennrich Oliver, Forchhammer Karl
Interfaculty Institute of Microbiology and Infection Medicine Tübingen, Department of Organismic Interactions, University of Tübingen, Tübingen, Germany.
Interfaculty Institute for Cell Biology, Department of Quantitative Proteomics, University of Tübingen, Tübingen, Germany.
Front Microbiol. 2019 Jun 25;10:1428. doi: 10.3389/fmicb.2019.01428. eCollection 2019.
P signal transduction proteins are widely spread among all domains of life where they regulate a multitude of carbon and nitrogen metabolism related processes. Non-diazotrophic cyanobacteria can utilize a high variety of organic and inorganic nitrogen sources. In recent years, several physiological studies indicated an involvement of the cyanobacterial P protein in regulation of ammonium, nitrate/nitrite, and cyanate uptake. However, direct interaction of P has not been demonstrated so far. In this study, we used biochemical, molecular genetic and physiological approaches to demonstrate that P regulates all relevant nitrogen uptake systems in sp. strain PCC 6803: P controls ammonium uptake by interacting with the Amt1 ammonium permease, probably similar to the known regulation of ammonium permease AmtB by the P homolog GlnK. We could further clarify that P mediates the ammonium- and dark-induced inhibition of nitrate uptake by interacting with the NrtC and NrtD subunits of the nitrate/nitrite transporter NrtABCD. We further identified the ABC-type urea transporter UrtABCDE as novel P target. P interacts with the UrtE subunit without involving the standard interaction surface of P interactions. The deregulation of urea uptake in a P deletion mutant causes ammonium excretion when urea is provided as nitrogen source. Furthermore, the urea hydrolyzing urease enzyme complex appears to be coupled to urea uptake. Overall, this study underlines the great importance of the P signal transduction protein in the regulation of nitrogen utilization in cyanobacteria.
P信号转导蛋白广泛分布于生命的所有领域，在这些领域中它们调节众多与碳和氮代谢相关的过程。非固氮蓝细菌可以利用多种有机和无机氮源。近年来，多项生理学研究表明，蓝细菌的P蛋白参与了铵、硝酸盐/亚硝酸盐和氰酸盐吸收的调节。然而，到目前为止，尚未证明P的直接相互作用。在本研究中，我们使用生化、分子遗传学和生理学方法来证明P调节集胞藻属PCC 6803菌株中所有相关的氮吸收系统：P通过与Amt1铵通透酶相互作用来控制铵的吸收，这可能类似于P同源物GlnK对铵通透酶AmtB的已知调节。我们可以进一步阐明，P通过与硝酸盐/亚硝酸盐转运蛋白NrtABCD的NrtC和NrtD亚基相互作用，介导铵和黑暗诱导的硝酸盐吸收抑制。我们进一步确定ABC型尿素转运蛋白UrtABCDE是新的P靶点。P与UrtE亚基相互作用，而不涉及P相互作用的标准相互作用表面。当以尿素作为氮源时，P缺失突变体中尿素吸收的失调会导致铵排泄。此外，尿素水解脲酶复合物似乎与尿素吸收相关联。总体而言，本研究强调了P信号转导蛋白在蓝细菌氮利用调节中的重要性。
