The YscU family of proteins are one of several proteins involved in assembly of the type III apparatus in gram-negative pathogenic and symbiotic bacteria. This protein in particular is important in the maturing of the type III pilus as it switches from secreting pilus subunits to secreting type III effectors. YscU-type proteins contain a transmembrane region within the N-terminal ~200 residues followed by a cytoplasmic domain; this cytoplasmic domain undergoes an auto-cleavage at a highly conserved Asn residue and this cleavage is key to the maturing of the type III pilus. Structures of the cytoplasmic domain of YscU from Yersinia, E. coli and Shigella have been solved in their non-mutated (cleaved) form (for example see PDB 2JLI and 2VT1) and mutated forms which are cleavage-inactive (PDB 2JLH, 2JLJ, 2W0R and 3C00) to determine differences between the pre- and post-cleaved conformation relevant for pilus maturation. As part of our understanding of the pilus maturation process we have undertaken structure determination of a number of proteins involved in this process including the chlamydial homologue of YscO (CT670, PDB 3K29) and the cleavage inactive cytoplasmic domain of the chlamydial YscU described here. Despite the ~30% sequence homology with YscU homologues whose structures have been reported, we find the chlamydial structure is virtually identical to those of other reported YscU homologues.