This entry represents the C-terminal domain of mitochondrial D-glutamate cyclase, which converts D-glutamate to 5-oxo-D-proline [1]. This is a conserved domain also found in uncharacterised proteins from bacteria and archaea. Structural studies of the hypothetical protein TON_0340 from Thermococcus onnurineus revealed an active-site cavity harbouring a metal-binding site containing six invariant aspartate and glutamate residues that adopts an alpha/beta-structure [2]. Biochemical and mutational analysis show that TON_0340 is a Mn+2-dependent phosphatase [2].

1: D-Glutamate is metabolized in the heart mitochondria. Ariyoshi M, Katane M, Hamase K, Miyoshi Y, Nakane M, Hoshino A, Okawa Y, Mita Y, Kaimoto S, Uchihashi M, Fukai K, Ono K, Tateishi S, Hato D, Yamanaka R, Honda S, Fushimura Y, Iwai-Kanai E, Ishihara N, Mita M, Homma H, Matoba S; Sci Rep. 2017;7:43911. PMID:28266638

2: Identification of a Highly Conserved Hypothetical Protein TON_0340 as a Probable Manganese-Dependent Phosphatase. Sohn YS, Lee SG, Lee KH, Ku B, Shin HC, Cha SS, Kim YG, Lee HS, Kang SG, Oh BH; PLoS One. 2016;11:e0167549. PMID:27907125