A protein lacking an essential input to its tertiary structure does fold into a compact globule

It is shown by equilibrium ultracentrifugation, velocity sedimentation, and viscometry that an N-truncated structural protein Caf1 (Cafl_13–149) of the Yersinia pestis capsular antigen fiber exists as a monomer in solution and is capable of folding from denatured state into a compact globular state by itself, without involvement of a chaperone or other subunits. This happens despite the fact that in the norm, important information on the tertiary structure of each Caf1 subunit (specifically, completion of its hydrophobic core) is provided by the “donor” segment Ala1-Thr12 of the neighboring fiber subunit.