Ligand-Dependent Dynamics of the Active-Site Lid in Bacterial Dimethylarginine Dimethylaminohydrolase
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- 作者：Masooma Rasheed ; Christine Richter ; Liisa T. Chisty ; John Kirkpatrick ; Martin Blackledge ; Martin R. Webb ; Paul C. Driscoll
- 刊名：Biochemistry
- 出版年：2014
- 出版时间：February 18, 2014
- 年：2014
- 卷：53
- 期：6
- 页码：1092-1104
- 全文大小：735K
- ISSN：1520-4995
文摘
The dimethylarginine dimethylaminohydrolase (DDAH) enzyme family has been the subject of substantial investigation as a potential therapeutic target for the regulation of vascular tension. DDAH enzymes catalyze the conversion of asymmetric N畏,N畏-dimethylarginine (ADMA) to l-citrulline. Here the influence of substrate and product binding on the dynamic flexibility of DDAH from Pseudomonas aeruginosa (PaDDAH) has been assessed. A combination of heteronuclear NMR spectroscopy, static and time-resolved fluorescence measurements, and atomistic molecular dynamics simulations was employed. A monodisperse monomeric variant of the wild-type enzyme binds the reaction product l-citrulline with a low millimolar dissociation constant. A second variant, engineered to be catalytically inactive by substitution of the nucleophilic Cys249 residue with serine, can still convert the substrate ADMA to products very slowly. This PaDDAH variant also binds l-citrulline, but with a low micromolar dissociation constant. NMR and molecular dynamics simulations indicate that the active site 鈥渓id鈥? formed by residues Gly17-Asp27, exhibits a high degree of internal motion on the picosecond-to-nanosecond time scale. This suggests that the lid is open in the apo state and allows substrate access to the active site that is otherwise buried. l-Citrulline binding to both protein variants is accompanied by an ordering of the lid. Modification of PaDDAH with a coumarin fluorescence reporter allowed measurement of the kinetic mechanism of the PaDDAH reaction. A combination of NMR and kinetic data shows that the catalytic turnover of the enzyme is not limited by release of the l-citrulline product. The potential to develop the coumarin鈥揚aDDAH adduct as an l-citrulline sensor is discussed.