| Autor: |
Seff, Amalia-Laura, Pilbák, Sarolta, Silaghi-Dumitrescu, Ioan, Poppe, László |
| Předmět: |
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| Zdroj: |
Journal of Molecular Modeling; Jul2011, Vol. 17 Issue 7, p1551-1563, 13p |
| Abstrakt: |
Possible reaction intermediates of the histidine ammonia-lyase (HAL) reaction were investigated within the tightly closed active site of HAL from Pseudomonas putida ( PpHAL). The closed structure of PpHAL was derived from the crystal structure of PpHAL inhibited with l-cysteine, in which the 39-80 loop including the catalytically essential Tyr53 was replaced. This modified loop with closed conformation was modeled using the structure of phenylalanine ammonia-lyase from Anabaena variabilis ( AvPAL) with a tightly closed active site as a template. Three hypothetical structures of the covalently bound intermediate in the PpHAL active site were investigated by conformational analysis. The distances between the acidic pro-S β-hydrogen of the ligand and the appropriate oxygen atoms of Tyr53, Ty280 and Glu414 − which may act as enzymic bases − in the conformations of the three hypothetical intermediate structures were analyzed together with the substrate and product arrangements. The calculations indicated that the most plausible HAL reaction pathway involves the N-MIO intermediate structure in which the L-histidine substrate is covalently bound to the N-3,5-dihydro-5-methylidene-4 H-imidazol-4-one (MIO) prosthetic group of the apoenzyme via the amino group. Density functional theory (DFT) calculations − on a truncated model of the N-MIO intermediate containing a Zn ion coordinated to the imidazole ring of the ligand and to His83, Met382 and a water molecule − indicated that Zn-complex formation plays a role in the reactivity and substrate specificity of HAL. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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