The formiminotransferase (FT) domain of formiminotransferase- cyclodeaminase (FTCD) forms a homodimer, and each protomer comprises two subdomains. The N-terminal subdomain is made up of a six-stranded mixed beta-pleated sheet and five alpha helices, which are arranged on the external surface of the beta sheet. This, in turn, faces the beta-sheet of the C-terminal subdomain to form a double beta-sheet layer. The two subdomains are separated by a short linker sequence, which is not thought to be any more flexible than the remainder of the molecule. The substrate is predicted to form a number of contacts with residues found in both the N-terminal and C-terminal subdomains.