Biochemical characterization of paralyzed flagellum proteins A (PflA) and B (PflB) from Helicobacter pylori flagellar motor

Motility by means of flagella plays an important role in the persistent colonization of Helicobacter pylori in the human stomach. The H. pylori flagellar motor has a complex structure that includes a periplasmic scaffold, the components of which are still being identified. Here, we report the isolation and characterization of the soluble forms of two putative essential H. pylori motor scaffold components, proteins PflA and PflB. We developed an on-column refolding procedure, overcoming the challenge of inclusion body formation in Escherichia coli. We employed mild detergent sarkosyl to enhance protein recovery and n-dodecyl-N,N-dimethylamine-N-oxide (LDAO)-containing buffers to achieve optimal solubility and monodispersity. In addition, we showed that PflA lacking the β-rich N-terminal domain is expressed in a soluble form, and behaves as a monodisperse monomer in solution. The methods for producing the soluble, folded forms of H. pylori PflA and PflB established in this work will facilitate future biophysical and structural studies aimed at deciphering their location and their function within the flagellar motor.