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 wa lls. The crystal structure of glutamate racemase from Aquifex pyrophilus, d etermined at 2.3 Angstrom resolution, reveals that the enzyme forms a dimer and each monomer consists of two alpha/beta fold domains, a unique structu re that has not been observed in other racemases or members of an enolase s uperfamily, A substrate analog, D-glutamine, binds to the deep pocket forme d by conserved residues from two monomers. The structural and mutational an alyses allow us to propose a mechanism of metal cofactor-independent glutam ate racemase in which two cysteine residues are involved in catalysis.