Shigella ssp cause bacillary dysentery (shigellosis) which has high global morbidity in young children and the elderly . The virulence of Shigella relies upon a type III secretion system (T3SS) which injects host altering effector proteins into targeted intestinal cells . The Shigella T3SS contains two components, invasion plasmid antigen D (IpaD) and invasion plasmid antigen B (IpaB), that were previously identified as broadly protective antigens . When IpaD and IpaB were co-expressed to give the DB fusion (DBF) protein, vaccine efficacy was further improved . Biophysical characterization under various pH conditions showed that DBF is most stable at pH 7 and 8 and loses its conformational integrity at 48 and 50 oC respectively . Forced degradation studies revealed significant effects on the secondary structure, tertiary structure and conformational stability of DBF . In the presence of phosphate buffers as well as other anionic excipients, DBF demonstrated a concentration dependent conformational stabilization . Molecular docking revealed potential polyanion binding sites in DBF that may interact with phytic acid . These sites can be exploited to stabilize the DBF protein . This work highlights potential destabilizing and stabilizing factors, which not only improves our understanding of the DBF protein but helps in future development of a stable Shigella vaccine.