Structures of Two Histidine Ammonia-Lyase Modifications and Implications for the Catalytic MechanismBaedeker, M., Schulz, G.E.
(2002) Eur J Biochem 269: 1790
- PubMed: 11895450
- DOI: https://doi.org/10.1046/j.1432-1327.2002.02827.x
- Primary Citation of Related Structures:
- PubMed Abstract:
Histidine ammonia-lyase (EC 188.8.131.52) catalyzes the nonoxidative elimination of the alpha-amino group of histidine using a 4-methylidene-imidazole-5-one (MIO), which is formed autocatalytically from the internal peptide segment 142Ala-Ser-Gly. The structure of the enzyme inhibited by a reaction with l-cysteine was established at the very high resolution of 1.0 A. Five active center mutants were produced and their catalytic activities were measured. Among them, mutant Tyr280-->Phe could be crystallized and its structure could be determined at 1.7 A resolution. It contains a planar sp2-hybridized 144-N atom of MIO, in contrast to the pyramidal sp3-hybridized 144-N of the wild-type. With the planar 144-N atom, MIO assumes the conformation of a putative intermediate aromatic state of the reaction, demonstrating that the conformational barrier between aromatic and wild-type states is very low. The data led to a new proposal for the geometry for the catalyzed reaction, which also applies to the closely related phenylalanine ammonia-lyase (EC 184.108.40.206). Moreover, it suggested an intermediate binding site for the released ammonia.
Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität, Freiburg im Breisgau, Germany.