Structure and mechanism of glutamate racemase from Aquifex pyrophilus

Glutamate racemase (MurI) is responsible for the synthesis of D-glutamate, an essential building block of the peptidoglycan layer in bacterial cell walls. The crystal structure of glutamate racemase from Aquifex pyrophilus, determined at 2.3 A resolution, reveals that the enzyme forms a dimer and each monomer consists of two alpha/beta fold domains, a unique structure that has not been observed in other racemases or members of an enolase superfamily. A substrate analog, D-glutamine, binds to the deep pocket formed by conserved residues from two monomers. The structural and mutational analyses allow us to propose a mechanism of metal cofactor-independent glutamate racemase in which two cysteine residues are involved in catalysis.