Structural and enzymatic properties of mammalian D-glutamate cyclase

D-Glutamate cyclase (DGLUCY) is a unique enzyme that reversibly converts free D-glutamate to 5-oxo-D-proline and H₂O. Mammalian DGLUCY is highly expressed in the mitochondrial matrix in the heart, and its downregulation disrupts D-glutamate and/or 5-oxo-D-proline levels, contributing to the onset and/or exacerbation of heart failure. However, detailed characterisation of DGLUCY has not yet been performed. Herein, the structural and enzymatic properties of purified recombinant mouse DGLUCY were examined. The results revealed a dimeric oligomerisation state, and both D-glutamate-to-5-oxo-D-proline and 5-oxo-D-proline-to-D-glutamate reactions were catalysed in a stereospecific manner. Catalytic activity is modulated by divalent cations and nucleotides including ATP and ADP. Interestingly, the presence of Mn²⁺ completely abolished the 5-oxo-D-proline-to-D-glutamate reaction but stimulated the D-glutamate-to-5-oxo-D-proline reaction. The optimum pH is ∼8.0, similar to that in the mitochondrial matrix, and the catalytic efficiency for D-glutamate is markedly higher than that for 5-oxo-D-proline. These findings suggest that DGLUCY functions as a metalloenzyme that degrades D-glutamate in the mitochondrial matrix in mammalian cells. The results also provide insight into the correlation between DGLUCY enzyme activity and the physiological and pathological roles of D-glutamate and 5-oxo-D-proline in cardiac function, which is of relevance to the risk of onset of heart failure.