1gkm

From Proteopedia

Revision as of 14:09, 5 November 2007

HISTIDINE AMMONIA-LYASE (HAL) FROM PSEUDOMONAS PUTIDA INHIBITED WITH L-CYSTEINE

Overview

Histidine ammonia-lyase (EC 4.3.1.3) 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 4.3.1.5)., Moreover, it suggested an intermediate binding site for the released, ammonia.

About this Structure

1GKM is a Single protein structure of sequence from Pseudomonas putida with SO4, CYS, O and GOL as ligands. Active as Histidine ammonia-lyase, with EC number 4.3.1.3 Structure known Active Site: MIO. Full crystallographic information is available from OCA.

Reference

Structures of two histidine ammonia-lyase modifications and implications for the catalytic mechanism., Baedeker M, Schulz GE, Eur J Biochem. 2002 Mar;269(6):1790-7. PMID:11895450

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