title: Structural and functional features in human PDE5A1 regulatory domain that provide for allosteric cGMP binding, dimerization, and regulation.
abstract: The cGMP-binding cGMP-specific phosphodiesterase (PDE5) contains a catalytic domain that hydrolyzes cGMP and a regulatory (R) domain that contains two GAFs (a and b; GAF is derived from the proteins mammalian cGMP-binding PDEs, Anabaena adenylyl cyclases, and Escherichia coli (FhlA)). The R domain binds cGMP allosterically, provides for dimerization, and is phosphorylated at a site regulated by allosteric cGMP binding. Quaternary structures and cGMP-binding properties of 10 human PDE5A1 constructs containing one or both GAFs were characterized. Results reveal that: 1) high affinity homo-dimerization occurs between GAF a modules (K(D) < 30 nM) and between GAF b modules (K(D) = 1-20 pM), and the sequence between the GAFs (Thr322-Asp403) contributes to dimer stability; 2) 176 amino acids (Val156-Gln331) in GAF a are adequate for cGMP binding; 3) GAF a has higher affinity for cGMP (K(D) < 40 nM) than does the isolated R domain (K(D) = 110 nM) or holoenzyme (K(D) = 200 nM), suggesting that the sequence containing GAF b and its flanking amino acids autoinhibits GAF a cGMP-binding affinity in intact R domain; 4) a mutant (Met1-Glu321) containing only GAF a has high affinity, biphasic cGMP-binding kinetics consistent with structural heterogeneity of GAF a, suggesting that the presence of GAF b is not required for biphasic cGMP-dissociation kinetics observed in holoenzyme or isolated R domain; 5) significant cGMP binding by GAF b was not detected; and 6) the sequence containing GAF b and its flanking amino acids is critical for cGMP stimulation of Ser102 phosphorylation by cyclic nucleotide-dependent protein kinases. Results yield new insights into PDE5 functions, further define boundaries that provide for allosteric cGMP binding, and identify regions that contribute to dimerization.
authors.affiliation: Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0615, USA.
authors.forename: Roya
authors.initials: R
authors.lastname: Zoraghi
authors.forename: Emmanuel P
authors.initials: EP
authors.lastname: Bessay
authors.forename: Jackie D
authors.initials: JD
authors.lastname: Corbin
authors.forename: Sharron H
authors.initials: SH
authors.lastname: Francis
mesh_terms: D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000737:chemistry* / Q000502:physiology; D000494:Allosteric Regulation; D020816:Amino Acid Motifs; D020134:Catalytic Domain; D000242:Cyclic AMP / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism*; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; D019281:Dimerization; D006801:Humans; D010766:Phosphorylation; D011487:Protein Conformation
chemical_list: D000242:Cyclic AMP; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; C517381:PDE5A protein, human; D006152:Cyclic GMP