Fig. (1) Tertiary and quaternary structure of human fumarase (PDB ID: 3E04 [40]). (A) A single subunit of human fumarase has been colored-coded by domain: domain 1 (D1) – red, domain 2 (D2) – yellow, and domain 3 (D3) – blue. (B) The human fumarase homotetramer has been colored by chain, with subunits labeled as A, B, C, or D. The all α-helical central domain, D2, forms the major intersubunit interface upon oligomerization. D1 and D3 domains lie at the corners of the homotetramer and outline the entry point to the four independent fumarase active sites.