Signal transduction and c-di-GMP second messenger: novel tools to investigare the mechanism of nutrient sensing.

Nutrients may dictate the fate of bacterial cell including biofilm formation by tuning the intracellular levels of c-di-GMP [1]. Many proteins involved in controlling c-di-GMP levels through diguanylate cyclase or phosphodiesterase domain (or both) are linked to periplasmic domains devoted to nutrient perceiving. Among nutrients, L-Arginine represents a key metabolite required as nitrogen, carbon and ATP source, associated to chronic infections, biofilm/virulence and antibiotic resistance [2]. Understanding the mechanism of L-Arginine-dependent signal transduction is crucial to identify possible strategies to tune biofilm through nutrients. Nevertheless, the architecture of such transducers is often too complex to be suitable for full-length studies, including many regulatory domains downstream the transmembrane helices joining the catalytic moiety (as in the case of RmcA from P. aeruginosa [3, 4]). To by-pass this limitation, we identify a possible prototype protein able to change c-di-GMP levels in response to L-Arginine, showing a minimal architecture i.e., periplasmic L-Arginine binding domain, transmembrane helices, catalytic domain(s). The purification as soluble protein arranged into nanodisc and its preliminary characterization is shown, in comparison with protein engineering studies aimed at producing a water-soluble version of the protein. 1. Dahlstrom et al. (2018) J Bacteriol. 200(8):e00703-17. 2. Rinaldo et al. (2018). FEMS Microbiol Lett., 365(6). 3. Paiardini et. al. (2018) Proteins. 86(10): 1088-1096. 4. Mantoni et al. (2018) FEBS J. 285(20): 3815-3834.