Flagellar hook capping protein - N-terminal region
FlgD is known to be absolutely required for hook assembly, yet it has not been detected in the mature flagellum. It appears to act as a hook-capping protein to enable assembly of hook protein subunits. FlgD regulates the assembly of the hook cap structure to prevent leakage of hook monomers into the medium and hook monomer polymerization and also plays a role in determination of the correct hook length, with the help of the FliK protein. This family represents the N-terminal conserved region of FlgD. A recent crystal structure showed that this region was likely to be flexible and was cleaved off during crystallisation.