Crystallization of the N-terminal regulatory domain of the enhancer-binding protein FleQ from Stenotrophomonas maltophilia

FleQ is a master regulator that controls bacterial flagellar gene expression. It is a unique enhancer-binding protein or repressor protein comprising an N-terminal FleQ domain, an AAA⁺/ATPase σ54-interaction domain and a helix–turn–helix DNA-binding domain. FleN is a putative ATPase with a deviant Walker A motif that works together with FleQ by binding to the FleQ N-terminal domain to fully express pel, psl and cdr operons in the presence of c-di-GMP to enhance biofilm formation. Stenotrophomonas maltophilia is an emerging human pathogen that causes fatal infections in humans. In order to understand the interaction between the FleN and FleQ domains and its effect on S. maltophilia biofilm formation, determination of the FleQ–c-di-GMP and FleN–FleQ–c-di-GMP complex structures was embarked upon. Towards this goal, the FleQ N-terminal domain from S. maltophilia was first cloned and expressed in Escherichia coli. Native and SeMet-labelled FleQ domains were successfully crystallized and diffracted to resolutions of 2.08 and 2.58 Å, respectively.