title: Co-crystal structures of PKG Iβ (92-227) with cGMP and cAMP reveal the molecular details of cyclic-nucleotide binding.
abstract: BACKGROUND
  Cyclic GMP-dependent protein kinases (PKGs) are central mediators of the NO-cGMP signaling pathway and phosphorylate downstream substrates that are crucial for regulating smooth muscle tone, platelet activation, nociception and memory formation. As one of the main receptors for cGMP, PKGs mediate most of the effects of cGMP elevating drugs, such as nitric oxide-releasing agents and phosphodiesterase inhibitors which are used for the treatment of angina pectoris and erectile dysfunction, respectively.
  
  
  RESULTS
  We have investigated the mechanism of cyclic nucleotide binding to PKG by determining crystal structures of the amino-terminal cyclic nucleotide-binding domain (CNBD-A) of human PKG I bound to either cGMP or cAMP. We also determined the structure of CNBD-A in the absence of bound nucleotide. The crystal structures of CNBD-A with bound cAMP or cGMP reveal that cAMP binds in either syn or anti configurations whereas cGMP binds only in a syn configuration, with a conserved threonine residue anchoring both cyclic phosphate and guanine moieties. The structure of CNBD-A in the absence of bound cyclic nucleotide was similar to that of the cyclic nucleotide bound structures. Surprisingly, isothermal titration calorimetry experiments demonstrated that CNBD-A binds both cGMP and cAMP with a relatively high affinity, showing an approximately two-fold preference for cGMP.
  
  
  CONCLUSIONS
  Our findings suggest that CNBD-A binds cGMP in the syn conformation through its interaction with Thr193 and an unusual cis-peptide forming residues Leu172 and Cys173. Although these studies provide the first structural insights into cyclic nucleotide binding to PKG, our ITC results show only a two-fold preference for cGMP, indicating that other domains are required for the previously reported cyclic nucleotide selectivity.
authors.affiliation: Department of Pharmacology, Baylor College of Medicine, Houston, Texas, United States of America.
authors.forename: Jeong Joo
authors.initials: JJ
authors.lastname: Kim
authors.forename: Darren E
authors.initials: DE
authors.lastname: Casteel
authors.forename: Gilbert
authors.initials: G
authors.lastname: Huang
authors.forename: Taek Hun
authors.initials: TH
authors.lastname: Kwon
authors.forename: Ronnie Kuo
authors.initials: RK
authors.lastname: Ren
authors.forename: Peter
authors.initials: P
authors.lastname: Zwart
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Headd
authors.forename: Nicholas Gene
authors.initials: NG
authors.lastname: Brown
authors.forename: Dar-Chone
authors.initials: DC
authors.lastname: Chow
authors.forename: Timothy
authors.initials: T
authors.lastname: Palzkill
authors.forename: Choel
authors.initials: C
authors.lastname: Kim
mesh_terms: D000595:Amino Acid Sequence; D001059:Apoproteins / Q000737:chemistry; D001665:Binding Sites; D002151:Calorimetry; D018360:Crystallography, X-Ray; D000242:Cyclic AMP / Q000737:chemistry*; D054756:Cyclic AMP-Dependent Protein Kinase RIalpha Subunit / Q000737:chemistry; D006152:Cyclic GMP / Q000737:chemistry*; D062965:Cyclic GMP-Dependent Protein Kinase Type I; D017869:Cyclic GMP-Dependent Protein Kinases / Q000737:chemistry*; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D040681:Structural Homology, Protein
chemical_list: D001059:Apoproteins; D054756:Cyclic AMP-Dependent Protein Kinase RIalpha Subunit; D008024:Ligands; D000242:Cyclic AMP; D062965:Cyclic GMP-Dependent Protein Kinase Type I; D017869:Cyclic GMP-Dependent Protein Kinases; C569718:PRKG1 protein, human; D006152:Cyclic GMP