<p>The molecule c-di-GMP is a bacterial second messenger that controls various processes such as motility or biofilm formation in bacteria [1]. To synthesize and degrade c-di-GMP, enzymes called diguanylate cyclases (DGC) containing a GGDEF-domain and phosphodiesterases (PDE) containing an EAL-domain or HD-GYP-domain are important [1, 2].<em> Pseudomonas aeruginosa</em>, a model organism for biofilm formation and dispersion, encodes for 18 GGDEF, 5 EAL, 16 GGDEF / EAL, and 3 HD-GYP-domain-containing proteins [3].<br />One of the GGDEF / EAL-containing proteins is NbdA. This protein also harbors an N-terminal membrane anchored MHYT-domain, that is predicted to be a sensor for NO, CO or O<sub>2</sub> [4]. In this work, recombinant and affinity purified NbdA was tested for its PDE activity. Three different methods were used to measure the PDE activity of NbdA: a bis-pNPP-assay in which the conversion of the pseudosubstrate bis-pNPP into p-nitrophenol was detected spectroscopically, an HPLC-analysis of an enzymatic assay with the native substrate c-di-GMP, and a MANT-c-di-GMP-assay in which a fluorescently labeled form of the presumed substrate c-di-GMP was utilized.<br />To establish these methods, the two known phosphodiesterases, PdeH from <em>Escherichia coli</em> [5] and RocR from <em>P. aeruginosa</em> [6], were also produced and tested. Subsequently, three variants of NbdA were investigated: the full-length version and two truncated versions of the protein. Activity was further assessed using functional complementation of an <em>E. coli</em> phosphodiesterase deficient strain with full-length and truncated NbdA variants confirming PDE activity <em>in vivo</em>.</p>
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<p>[1] Hengge, R. (2009) Nature Rev. Microbiol. 7: 263-273.</p>
<p>[2] R&#246;mling, U., Gomelsky, M., Galperin, M.Y. (2005). Mol. Microbiol. 57: 629&#8211;639.</p>
<p>[3] Valentini, M., Filloux, A. (2016). J. Biol. Chem. 291: 12547&#8211;12555.</p>
<p>[4] Galperin, M.Y., Gaidenko, T.A., Mulkidjanian, A.Y., Nakano, M., und Price, C.W. (2001). FEMS Microbiol. Lett. 205, 17&#8211;23.</p>
<p>[5] Pesavento, C., Becker, G., Sommerfeldt, N., Possling, A., Tschowri, N., Mehlis, A., Hengge, R. (2008). Genes Dev. 22: 2434&#8211;2446.</p>
<p>[6] Chen et al. (2012) Chen, M.W., Kotaka, M., Vonrhein, C., Bricogne, G., Rao, F., Chuah, M.L.C., Svergun, D., Schneider, G., Liang, Z.-X., Lescar, J.&#160; (2012). Signaling. J. Bacteriol. 194: 4837&#8211;4846</p>
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