Previously uncharacterized aliphatic amino acid positions modulate the apparent catalytic activity of the EAL domain of ZMO_1055 and other cyclic di-GMP specific EAL phosphodiesterases

The ubiquitous second messenger cyclic di-GMP signaling system decides bacterial life style transition between sessility and motility. GGDEF diguanylate cyclase and EAL phosphodiesterase domains conventionally direct the turnover of this signaling molecule being subject to micro- and macroevolution. While the highly conserved signature amino acids involved in divalent ion binding and catalysis have readily been identified, recognition of amino acid substitutions that modulate the catalytic activity is rare. Associated with development towards cellulose-mediated self-flocculation in Zymomonas mobilis ZM401, the A526V substitution, previously not been recognized to affect the functionality of the EAL domain, downregulates the apparent catalytic activity of the PAS-GGDEF-EAL ZMO1055 phosphodiesterase compared to parental Z. mobilis ZM4 and equally in homologous protein domains independently of the genetic background. Substitution of A526, which is conserved among homologs, with amino acids with longer aliphatic side chains than valine have an even more pronounced effect. Thus single amino acid substitutions that lead to alterations in the catalytic activity of cyclic di-GMP turnover domains amplify the signaling output and thus significantly contribute to the flexibility and adaptability of the cyclic di-GMP signaling network. In this context, ZMO1055 seems to be a current evolutionary target.