ATPase component of the type III secretion system (T3SS), also called injectisome, which is used to inject bacterial effector proteins into eukaryotic host cells (PubMed:15060043, PubMed:16208377, PubMed:26170413). Acts as a molecular motor to provide the energy that is required for the export of proteins (Probable). Required for type III secretion apparatus (T3SA) formation, proper protein secretion, host cell invasion and virulence (PubMed:8045880, PubMed:14762212, PubMed:15060043, PubMed:26170413). May play a critical role in T3SS substrate recognition, disassembly of the effector/chaperone complex and unfolding of the effector in an ATP-dependent manner prior to secretion (PubMed:16208377). Releases the effector protein SptP from the chaperone SicP in an ATP-dependent manner (PubMed:16208377). ATP + H2O + cellular proteinSide 1 = ADP + phosphate + cellular proteinSide 2. The core secretion machinery of the T3SS is composed of approximately 20 different proteins, including cytoplasmic components, a base, an export apparatus and a needle (PubMed:30107569, PubMed:28283062). This subunit is part of the cytosolic complex (PubMed:15060043, PubMed:31288030, PubMed:28283062). Forms homohexamers (PubMed:15060043, PubMed:28283062). Interacts directly with OrgB/SctL (stator protein) and InvI/SctO (stalk protein) (PubMed:15060043, PubMed:31288030, PubMed:28283062). Forms a complex with SpaO/SctQ and OrgB/SctL (PubMed:31288030). Interacts with the chaperone/effector protein complex SicP-SptP via its C terminus (PubMed:16208377). Interacts with the effector protein SopD (PubMed:20185511). Associated with the membrane, presumably through interactions with other components of the SPI-1-encoded T3SS. Binding of ATP leads to conformational changes of two loops located outside of the catalytic site. These changes could be critical for interaction with the stalk protein InvI/SctO or with chaperone and effector proteins during type III secretion. Deletion of the gene affects the overall stability of the cytoplasmic sorting platform (PubMed:28283062). Disruption mutant is defective in its ability to enter cultured epithelial cells (PubMed:8045880). Belongs to the ATPase alpha/beta chains family. T3SS ATPase subfamily.