The Carboxy-Terminal Region of Flavobacterium johnsoniae SprB Facilitates Its Secretion by the Type IX Secretion System and Propulsion by the Gliding Motility Machinery

TheF. johnsoniae gliding motility adhesin SprB is delivered to the cell surface by the type IX secretion system (T9SS) and is rapidly propelled along the cell by the motility machinery. How this 6,497-amino-acid protein interacts with the secretion and motility machines is not known. Fusion of the C-terminal 218 amino acids of SprB to a foreign cargo protein resulted in its secretion, attachment to the cell surface, and rapid movement by the motility machinery. Efficient secretion of SprB required coexpression with the outer membrane protein SprF. Secreted proteins that have sequence similarity to SprB in their C-terminal regions are common in the phylumBacteroidetes and may have roles in adhesion, motility, and virulence.