title: Characterization of a catalytic ligand bridging metal ions in phosphodiesterases 4 and 5 by molecular dynamics simulations and hybrid quantum mechanical/molecular mechanical calculations.
abstract: Cyclic nucleotide phosphodiesterases (PDEs) constitute a large superfamily of enzymes regulating concentrations of intracellular second messengers cAMP and cGMP through PDE-catalyzed hydrolysis. Although three-dimensional x-ray crystal structures of PDE4 and PDE5 have been reported, it is uncertain whether a critical, second bridging ligand (BL2) in the active site is H2O or HO- because hydrogen atoms cannot be determined by x-ray diffraction. The identity of BL2 is theoretically determined by performing molecular dynamics simulations and hybrid quantum mechanical/molecular mechanical (QM/MM) calculations, for the first time, on the protein structures resolved by x-ray diffraction. The computational results confirm our previous suggestion, which was based on QM calculations on a simplified active site model, that BL2 in PDE4 should be HO-, rather than H2O, serving as the nucleophile to initialize the catalytic hydrolysis of cAMP. The molecular dynamics simulations and QM/MM calculations on PDE5 demonstrate for the first time that the BL2 in PDE5 should also be HO- rather than H2O as proposed in recently published reports on the x-ray crystal structures, which serves as the nucleophile to initialize the PDE5-catalyzed hydrolysis of cGMP. These fundamental structural insights provide a rational basis for future structure-based drug design targeting PDEs.
authors.affiliation: Key Laboratory of Pesticide & Chemical Biology of Ministry of Education, College of Chemistry, Central China Normal University, Wuhan 430079, People's Republic of China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Xiong
authors.forename: Hai-Ting
authors.initials: HT
authors.lastname: Lu
authors.forename: Yongjian
authors.initials: Y
authors.lastname: Li
authors.forename: Guang-Fu
authors.initials: GF
authors.lastname: Yang
authors.forename: Chang-Guo
authors.initials: CG
authors.lastname: Zhan
mesh_terms: D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000737:chemistry* / Q000648:ultrastructure*; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D001665:Binding Sites; D002384:Catalysis; D003198:Computer Simulation; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; D004789:Enzyme Activation; D007477:Ions / Q000737:chemistry; D008024:Ligands; D019563:Mechanics; D008670:Metals / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D009038:Motion; D010727:Phosphoric Diester Hydrolases / Q000737:chemistry* / Q000648:ultrastructure*; D011485:Protein Binding; D011487:Protein Conformation; D011789:Quantum Theory; D013314:Stress, Mechanical
chemical_list: D007477:Ions; D008024:Ligands; D008670:Metals; D010727:Phosphoric Diester Hydrolases; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5