環状ジーグMP: バイ菌の行動の重要な役割

タイトル: 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

概要: The ubiquitous second messenger cyclic di-GMP is the most abundant diffusible nucleotide signalling system in bacteria deciding the life style transition between sessility and motility. GGDEF diguanylate cyclases and EAL phosphodiesterases conventionally direct the turnover of this signaling molecule. Thereby, those domains are subject to micro- and macroevolution with the evolutionary forces that promote alterations in these proteins currently mostly unknown. While the highly conserved signature amino acids involved in divalent ion binding and catalysis equally as signal transduction modules have been readily identified, more subtle amino acid substitutions that modulate the catalytic activity have been rarely recognized and their molecular mechanism characterized. Our previous work identified the A526V substitution to be involved in downregulation of the apparent catalytic activity of the Zymomonas mobilis ZM4 PAS-GGDEF-EAL ZMO1055 phosphodiesterase and leading to a self-flocculation phenotype mediated by elevated production of the exopolysaccharide cellulose in Z. mobilis ZM401. As A526 is located at a position that has previously not been recognized to affect the catalytic activity of the EAL domain, we further investigated the molecular mechanisms and the functional conservation of this substitution. Using a number of model systems, our results indicate that the alanine at position 526 is highly conserved in ZMO1055 homologs and beyond with the A526V mutation to alter the apparent phosphodiesterase activity in subgroups of EAL domains. Thus we hypothesize that 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.