Enzymatic Activity and Thermodynamic Stability of Biliverdin IXβ Reductase Are Maintained by an Active Site Serine
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- 作者：Dr. Wen-Ting Chu ; Dr. Natasha M. Nesbitt ; Dr. Dmitri V. Gnatenko ; Dr. Zongdong Li ; Beibei Zhang ; Dr. Markus A. Seeliger ; Dr. Seamus Browne ; Prof. Timothy J. Mantle ; Prof. Wadie F. Bahou and Prof. Jin Wang
- 刊名：Chemistry - A European Journal
- 出版年：2017
- 出版时间：February 3, 2017
- 年：2017
- 卷：23
- 期：8
- 页码：1891-1900
- 全文大小：3233K
- ISSN：1521-3765
文摘
Biliverdin reductase IXβ (BLVRB) is a crucial enzyme in heme metabolism. Recent studies in humans have identified a loss-of-function mutation (Ser111Leu) that unmasks a fundamentally important role in hematopoiesis. We have undertaken experimental and thermodynamic modeling studies to provide further insight into the role of the cofactor in substrate accessibility and protein folding properties regulating BLVRB catalytic mechanisms. Site-directed mutagenesis with molecular dynamic (MD) simulations establish the critical role of NAD(P)H-dependent conformational changes on substrate accessibility by forming the “hydrophobic pocket”, along with identification of a single key residue (Arg35) modulating NADPH/NADH selectivity. Loop80 and Loop120 block the hydrophobic substrate binding pocket in apo BLVRB (open), whereas movement of these structures after cofactor binding results in the “closed” (catalytically active) conformation. Both enzymatic activity and thermodynamic stability are affected by mutation(s) involving Ser111, which is located in the core of the BLVRB active site. This work 1) elucidates the crucial role of Ser111 in enzymatic catalysis and thermodynamic stability by active site hydrogen bond network; 2) defines a dynamic model for apo BLVRB extending beyond the crystal structure of the binary BLVRB/NADP+ complex; 3) provides a structural basis for the “encounter” and “equilibrium” states of the binary complex, which are regulated by NAD(P)H.