文摘
Industrial production of antibiotics, such as semisynthetic penicillins and cephalosporins, requiresoptically pure D-p-hydroxylphenylglycine and its derivatives as important side-chain precursors. To produceoptically pure D-amino acids, microbial D-hydantoinase (E.C. 3.5.2.2) is used for stereospecific hydrolysisof chemically synthesized cyclic hydantoins. We report the apo-crystal structure of D-hydantoinase fromB. stearothermophilus SD1 at 3.0 Å resolution. The structure has a classic TIM barrel fold. Despite anundetectable similarity in sequence, D-hydantoinase shares a striking structural similarity with the recentlysolved structure of dihydroorotase. A structural comparison of hydantoinase with dihydroorotase revealedthat the catalytic chemistry is conserved, while the substrate recognition is not. This structure providesinsight into the stereochemistry of enantioselectivity in hydrolysis and illustrates how the enzyme recognizesstereospecific exocyclic substituents and hydrolyzes hydantoins. It should also provide a rationale forfurther directed evolution of this enzyme for hydrolysis of new hydantoins with novel exocyclic substituents.