Monomer in solution (PubMed:22658749). Interacts with OmpF/OmpC at the periplasmic face of the membrane (PubMed:22658749). The outer membrane proteins OmpF, OmpC and OmpX are involved in YebF export. OmpX may help target and load YebF onto the OmpF/OmpC porins. Contains an ordered core and an extensive dynamic surface formed by two regions, dynamic loop1 and dynamic loop2. The core is stabilized by a disulfide and ressembles the cystatin family. Belongs to the YebF family.