Formyl‐CoA transferase encloses the CoA binding site at the interface of an interlocked dimer

Formyl‐CoA transferase catalyses transfer of CoA from formate to oxalate in the first step of oxalate degradation by Oxalobacter formigenes , a bacterium present in the intestinal flora which is implicated in oxalate catabolism in mammals. Formyl‐CoA transferase is a member of a family of CoA‐transferases for which no structural information is available. We now report the three‐dimensional structure of O.formigenes formyl‐CoA transferase, which reveals a novel fold and a very striking assembly of the homodimer. The subunit is composed of a large and a small domain where residues from both the N‐ and C‐termini of the subunit are part of the large domain. The linkers between the domains give the subunit a circular shape with a hole in the middle. The enzyme monomers are tightly interacting and are interlocked. This fold requires drastic rearrangement of ∼75 residues at the C‐terminus for formation of the dimer. The structure of a complex of formyl‐CoA transferase with CoA is also reported and sets the scene for a mechanistic understanding of enzymes of this family of CoA‐transferases.