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From Proteopedia

Introduction

PDE5, phosphodiesterase 5 (EC 3.1.4.35), is an abundant protein in cell of airway and visceral smooth muscle and vascular cell. It can be found in epithelial cell and in Purkinje cell of the cerebella ^[1] and platelets and Corpus Cavernosum. In particular, it is implied in the NO pathway of penile erection and so in the Erectile Dysfunction (ED) ^[2].
There are 11 families of PDE (from 1 to 9), there is 21 genes for PDE which code 60 different PDE. For the PDE5A, the only PDE5 subcategory, there are 4 isoforms but their catalytic domain is the same ^[3].
The catalytic reaction is the hydrolysis of guanosine cyclic monophosphate into linear guanosine monophosphate. This cGMP-specific enzyme have 3 domains (from N terminal to C terminal) : GAF A, GAF B and a conserved catalytic domain regard to other PDEs of the family. Only cGMP can bind GAF A or GAF B and it stimulates the hydrolysis.
We study here the PDE5A catalytic fragment formed of amino acid residues from the 535th to the 860th ^[4]. In the inhibition, we talk about the Sildenafil mostly, because it's the most known (active ingredient in the Viagra®).
Problem in the PBD files: N-loop (from the 788th to the 881th residues) is not complete.

Structure of catalytic site

The only catalytic fragment is effective, so the regulations sites and the dimerization to a trimeric enzyme are useless for the catalytic activity. Moreover, this catalytic moiety has the same activity that the wild-type enzyme, so maybe the enzyme is monomeric in the cell ^[5]. Catalytic domain is conserved for the PDE family, between 20% and 40%, and the variant reactions of the PDE inhibitors on the different PDEs may be caused by the more variant regulatory sites ^[6].
The catalytic domain has 3 helical subdomains ^[7]:

• A N-terminal cyclin-fold region with eight helixes ^[8]: 5 α-helixes (1, 3, 5, 6 and 8) and 3 3ind10-helixes (2,4, and 7),.
  
• A linker domain: two antiparallels α9 and α10 helixes, and between a disordered region,.
  
• A C-terminal buddle pocket with eight helixes: 5 long α-helixes (11, 12, 14, 17 and 18) and 3 smaller helixes (13, 15 and 16),.
  
  • α5, 6 and 8 surround α3 and form an interface with the linker domain and the CTD.
    

The catalytic site is a pocket which is 330Å in volume and a deep of 10Å, with a narrow entry. There are 4 regions: M (with 2 metallic ions), H (hydrophobic), Q (for the substrate), L (the lid or “H-Loop” on both N-term and linker domain). M site is surrounded by the helixes α6, 8, 9, 10 and 12. A majority of aliphatic or hydrophobic residues, that creates the hydrophobic pocket ^[9].

M site contains:

• The Me-1 and Me-2 sites are occupied by metal ions, Zinc within Me-1 and within Me-2, Zinc, Magnesium or Manganese ^[10],
  
• The residues and two H2O (W1 et W2) binding zinc:
  
  • The crucial ^[11] and the conserved His617 and 653^[12], which bind one Zinc ion, are fundamental for the catalytic activity.
    
  • is critical for catalytic activity, but it isn't implied in the formation of the hydrophobic pocket. In fact, even if are lost and so the Zn not bound, a massive addition of Manganese^[13] in the medium allows a reactivation of catalysis.
    
• W2 binds ^[14],
  
• And there are 3 hydrogen bonds between 3 H2O and the conserved resides ^[15].
  

Q site contains:

• In particular the conserved residues
  
• The hydrogen bonds, between , imply an interaction between and the cGMP purine. Thus, it improves the specificity for the cGMP, against cAMP. ^[16]
  
• And bind the cGMP through this pyrazol ring and π-π interactions between Gln817 and the phenyl ring. ^[17]
  
  • So, the conserved hydrophobic residue is critical in the maintaining of the affinity. ^[18]
    

H site:

• In particular the residues . ^[19]
  

L site:

• In particular the hydrophobic residues . ^[20]
  

Besides, the kcat of the catalytic fragment decreases 40-fold and 8-fold if the residues are mutated, and so there are important in the catalytic activity ^[21]. Two others residues are significant: which is important for cGMP affinity but have no impact on cAMP affinity H-loop ^[22] and the conserved which is important for substrate affinity and catalytic activity because it determinates H-loop conformation ^[23] (see below).
H-loop is important in the substrate recognition and the interactions with, it is . H-loop has the same interactions with cGMP and Sildenafil (cf. Inhibitor) because it's related to its role of substrate binding^[24]. But The H-loop is not well understood, because when it's modified, the enzyme's function is practically not modified.^[25] But it also may have a role for inhibitor fixation.
Nowadays catalysis mechanism is not well know: there could be a, nucleophile attack of a water molecule on the substrate ^[26].

Inhibition

In the treatment erection dysfunction, the inhibitors Sildenafil, Vardenafil and Tadalafil are used, like in the pulmonary hypertension^[27]. Sildenafil may cure sleeping trouble after a intercontinental travel ^[28], may help to recover neural liaisons after an injury (the motor function^[29] and the sensory motor function^[30]) and can be vascular effects.

500px|Sildenafil Inhibitor, R1 in blue, R2 in green and R3 in red

500px|Sildenafil Inhibitor in the space in the enzyme

• PDE5 inhibitors might help physical condition in Duchene muscular dystrophy^[31], improve of cognitive function ^[32]and have antidepressant effect^[33] , also they might have an artero^[34] and endothelial cell protective effect^[35] so they have cardiac protection effect^[36] (controversial, cf. clinical trial “RELAX”), finally they slow tumer cell growth (Tadalafil-like)^[37]
  
• There are other PDE5 inhibitors: IBMX, Icarisid II and Udenafil.
  
• No interaction between the M site and the inhibitors
  

For the Sildenafil:

• 3 parts (R1: pyrazolopyrimidinone group; R2: ethoxyphenyl; R3: methylpiperazine)
  
• It is bound near Metallic ions but does not interact with them.
  

Binding amino acid for the Sildenafil:

• R1 group have contacts with (2 hydrogen bounds, so it increases Sildenafil affinity), (Sildenafil stacks against it), (hydrogen bound so it increases Sildenafil affinity ^[38]), and ^[39]. And there is hydrophobic interactions between the pyrazol ring and residues ^[40].
  
• R2 group is in the H pocket and has Van der Waals bounds with Val 782, Ala 783, Phe 786, Leu 804, Ile 813, Gln 817, Phe801. And interaction Pi-Pi between the phenyl ring and the Phe820.
  
• R3 group is in the L pocket and has contacts with
• is modified by Sildenafil presence in PDE5, ϕ and φ angles are increased (from 76-105° to 104-109° for ϕ and from 3-22° to 139-141° for φ) and ω angle is not changed. ^[41]
  

H-loop:
For each inhibitor, take a different and originally (comparatively to other PDEs) tertiary structure (and there are also minor modifications of ):

• For an unliganded PDE5, take a coil conformation. ^[42]
  
• In case of Sildenafil binding, a turn and an 3ind10 appear, and The all loop cover the active site (by migrate of 24 Å from unliganded PDE5 loop structure, so the active site become a closed pocket). ^[43]
  
• H-loop is less important in the interactions for Sildenafil and Icarisid II than cGMP.
  

Regulation

As it is written over, there are 2 regulatory domains (GAF A and GAF B). In cGMP pathway, PDE5 allows a negative feedback of the molecule: first, in presence of cGMP, it binds GAF A which stimulates the catalysis in the active site, and vice versa. Moreover, cGMP actives PKG which phophorylates PDE5, that is stimulated by the presence of cGMP on the GAF A or/and the active site. If the protein is not binding with cGMP but it is phophorylated, that stimulates the binding of cGMP on GAF A and the catalytic site. So cGMP presence overstimulates the catalysis ^[44]. And it also increase inhibitor's affinity^[45] and without cGMP, inhibitor don’t bind the PDE5 ^[46].

The NO Pathway

In the penile erection example, the nervous cell and/or epithelial cells are produced Nitrogen Oxide (NO) by the NOS (NO synthetase) from L-arginine and O2. They release NO in the extracellular environment going into vascular smooth cells and binding the Guanylyl Cyclase. This enzyme synthesizes cGMP from GMP, which stimulates the PKG. Finally, the calcium level is lower and the muscle cell relaxes and the Corpus Cavernosum rigidity increases. The PDE5 regulates the cGMP level making a negative feedback and can stop the rigidity. ^[47]

</StructureSection>

References

1. ↑ Francis SH, Zoraghi R, Kotera J, Ke H, Bessay EP, Blount MA, Corbin JD. Phosphodiesterase-5: molecular characteristics relating to structure, function, and regulation. In: Cyclic Nucleotide Phosphodiesterases in Health and Disease, edited by Beavo JA, Houslay MD, Francis SH. Boca Raton, FL: CRC, 2006, p. 131–164.
   Sekiguchi M, Hoshizaki H, Adachi H, Ohshima S, Taniguchi K, Kurabayashi M. Effects of antiplatelet agents on subacute thrombosis and restenosis after successful coronary stenting: a randomized comparison of ticlopidine and cilostazol. Circ J 68: 610–614, 2004. Sopory S, Kaur T, Visweswariah SS. The cGMP-binding, cGMPspecific phosphodiesterase (PDE5): intestinal cell expression, regulation and role in fluid secretion. Cell Signal 16: 681–692, 2004.
   Zhu B, Strada S, Stevens T. Cyclic GMP-specific phosphodiesterase 5 regulates growth and apoptosis in pulmonary endothelial cells. Am J Physiol Lung Cell Mol Physiol 289: L196–L206, 2005.
   
2. ↑ JD Corbin, Mechanisms of action of PDE5 inhibition in erectile dysfunction, International Journal of Impotence Research (2004) 16, S4–S7
3. ↑ Byung-Je Sung, Kwang Yeon Hwang, Young Ho Jeon, Jae Il Lee, Yong-Seok Heo, Jin Hwan Kim, Jinho Moon, Jung Min Yoon, Young-Lan Hyun, Eunmi Kim, Sung Jin Eum, Sam-Yong Park, Jie-Oh Lee, Tae Gyu Lee, Seonggu Ro & Joong Myung Cho, Structure of the catalytic domain of human phosphodiesterase 5 with bound drug molecules, NATURE, VOL 425, 4 SEPTEMBER 2003
4. ↑ http://www.rcsb.org/pdb/explore.do?structureId=2H40
5. ↑ Byung-Je Sung, Kwang Yeon Hwang, Young Ho Jeon, Jae Il Lee, Yong-Seok Heo, Jin Hwan Kim, Jinho Moon, Jung Min Yoon, Young-Lan Hyun, Eunmi Kim, Sung Jin Eum, Sam-Yong Park, Jie-Oh Lee, Tae Gyu Lee, Seonggu Ro & Joong Myung Cho, Structure of the catalytic domain of human phosphodiesterase 5 with bound drug molecules, NATURE, VOL 425, 4 SEPTEMBER 2003
6. ↑ Tamara L. Fink, Sharron H. Francis, Alfreda Beasley, Kennard A. Grimes, and Jackie D. Corbin, Expression of an Active, Monomeric Catalytic Domain of the cGMP-binding cGMP-specific Phosphodiesterase (PDE5), The Journal Of Biological Chemistry, Vol. 274, No. 49, Issue of December 3, pp. 34613–34620, 1999.
7. ↑ Byung-Je Sung, Kwang Yeon Hwang, Young Ho Jeon, Jae Il Lee, Yong-Seok Heo, Jin Hwan Kim, Jinho Moon, Jung Min Yoon, Young-Lan Hyun, Eunmi Kim, Sung Jin Eum, Sam-Yong Park, Jie-Oh Lee, Tae Gyu Lee, Seonggu Ro & Joong Myung Cho, Structure of the catalytic domain of human phosphodiesterase 5 with bound drug molecules, NATURE, VOL 425, 4 SEPTEMBER 2003
8. ↑ Jeffrey, P. D. et al. Mechanism of CDK activation revealed by the structure of a cyclinA–CDK2 complex. Nature 376, 313–320 (1995).
   Nikolov, D. B. et al. Crystal structure of a TFIIB-TBP-TATA-element ternary complex. Nature 377, 119–128 (1995).
9. ↑ Zoraghi R, Francis SH, Corbin JD. Critical amino acids in phosphodiesterase-5 catalytic site that provide for high-affinity interaction with cGMP and inhibitors. Biochemistry 46: 13554–13563, 2007.
10. ↑ Liu S, Mansour MN, Dillman KS, Perez JR, Danley DE, Aeed PA, Simons SP, Lemotte PK, Menniti FS. Structural basis for the catalytic mechanism of human phosphodiesterase 9. Proc Natl Acad Sci USA 105: 13309–13314, 2008.
11. ↑ Turko IV, Francis SH, Corbin JD. Potential roles of conserved amino acids in the catalytic domain of the cGMP-binding cGMPspecific phosphodiesterase. J Biol Chem 273: 6460–6466, 1998.
12. ↑ Francis SH, Turko IV, Grimes KA, Corbin JD. Histidine-607 and histidine-643 provide important interactions for metal support of catalysis in phosphodiesterase-5. Biochemistry 39: 9591–9596, 2000.
13. ↑ Francis SH, Turko IV, Grimes KA, Corbin JD. Histidine-607 and histidine-643 provide important interactions for metal support of catalysis in phosphodiesterase-5. Biochemistry 39: 9591–9596, 2000.
14. ↑ Byung-Je Sung, Kwang Yeon Hwang, Young Ho Jeon, Jae Il Lee, Yong-Seok Heo, Jin Hwan Kim, Jinho Moon, Jung Min Yoon, Young-Lan Hyun, Eunmi Kim, Sung Jin Eum, Sam-Yong Park, Jie-Oh Lee, Tae Gyu Lee, Seonggu Ro & Joong Myung Cho, Structure of the catalytic domain of human phosphodiesterase 5 with bound drug molecules, NATURE, VOL 425, 4 SEPTEMBER 2003
15. ↑ Byung-Je Sung, Kwang Yeon Hwang, Young Ho Jeon, Jae Il Lee, Yong-Seok Heo, Jin Hwan Kim, Jinho Moon, Jung Min Yoon, Young-Lan Hyun, Eunmi Kim, Sung Jin Eum, Sam-Yong Park, Jie-Oh Lee, Tae Gyu Lee, Seonggu Ro & Joong Myung Cho, Structure of the catalytic domain of human phosphodiesterase 5 with bound drug molecules, NATURE, VOL 425, 4 SEPTEMBER 2003
16. ↑ Byung-Je Sung, Kwang Yeon Hwang, Young Ho Jeon, Jae Il Lee, Yong-Seok Heo, Jin Hwan Kim, Jinho Moon, Jung Min Yoon, Young-Lan Hyun, Eunmi Kim, Sung Jin Eum, Sam-Yong Park, Jie-Oh Lee, Tae Gyu Lee, Seonggu Ro & Joong Myung Cho, Structure of the catalytic domain of human phosphodiesterase 5 with bound drug molecules, NATURE, VOL 425, 4 SEPTEMBER 2003
17. ↑ Byung-Je Sung, Kwang Yeon Hwang, Young Ho Jeon, Jae Il Lee, Yong-Seok Heo, Jin Hwan Kim, Jinho Moon, Jung Min Yoon, Young-Lan Hyun, Eunmi Kim, Sung Jin Eum, Sam-Yong Park, Jie-Oh Lee, Tae Gyu Lee, Seonggu Ro & Joong Myung Cho, Structure of the catalytic domain of human phosphodiesterase 5 with bound drug molecules, NATURE, VOL 425, 4 SEPTEMBER 2003
18. ↑ Turko IV, Francis SH, Corbin JD. Potential roles of conserved amino acids in the catalytic domain of the cGMP-binding cGMPspecific phosphodiesterase. J Biol Chem 273: 6460–6466, 1998.
19. ↑ Byung-Je Sung, Kwang Yeon Hwang, Young Ho Jeon, Jae Il Lee, Yong-Seok Heo, Jin Hwan Kim, Jinho Moon, Jung Min Yoon, Young-Lan Hyun, Eunmi Kim, Sung Jin Eum, Sam-Yong Park, Jie-Oh Lee, Tae Gyu Lee, Seonggu Ro & Joong Myung Cho, Structure of the catalytic domain of human phosphodiesterase 5 with bound drug molecules, NATURE, VOL 425, 4 SEPTEMBER 2003
20. ↑ Byung-Je Sung, Kwang Yeon Hwang, Young Ho Jeon, Jae Il Lee, Yong-Seok Heo, Jin Hwan Kim, Jinho Moon, Jung Min Yoon, Young-Lan Hyun, Eunmi Kim, Sung Jin Eum, Sam-Yong Park, Jie-Oh Lee, Tae Gyu Lee, Seonggu Ro & Joong Myung Cho, Structure of the catalytic domain of human phosphodiesterase 5 with bound drug molecules, NATURE, VOL 425, 4 SEPTEMBER 2003
21. ↑ Liu S, Mansour MN, Dillman KS, Perez JR, Danley DE, Aeed PA, Simons SP, Lemotte PK, Menniti FS. Structural basis for the catalytic mechanism of human phosphodiesterase 9. Proc Natl Acad Sci USA 105: 13309–13314, 2008.Turko IV, Francis SH, Corbin JD. Potential roles of conserved amino acids in the catalytic domain of the cGMP-binding cGMPspecific phosphodiesterase. J Biol Chem 273: 6460–6466, 1998.
22. ↑ Zoraghi R, Corbin JD, Francis SH. Phosphodiesterase-5 Gln817 is critical for cGMP, vardenafil, or sildenafil affinity: its orientation impacts cGMP but not cAMP affinity. J Biol Chem 281: 5553–5558, 2006.
23. ↑ Huanchen Wang, Yudong Liu, Qing Huai, Jiwen Cai, Roya Zoraghi, Sharron H. Francis, Jackie D. Corbin, Howard Robinson, Zhongcheng Xin, Guiting Lin, and Hengming Ke Zhongcheng Xin, Guiting Lin and Hengming Jackie D. Corbin, Howard Robinson, Jiwen Cai, Roya Zoraghi, Sharron H. Francis, Huanchen Wang, Yudong Liu, Qing Huai, Multiple Conformations of Phosphodiesterase-5: implications for enzyme function and drug development, The Journal of Biological Chemistry VOL. 281, NO. 30, pp. 21469–21479, July 28, 2006
24. ↑ Huanchen Wang, Yudong Liu, Qing Huai, Jiwen Cai, Roya Zoraghi, Sharron H. Francis, Jackie D. Corbin, Howard Robinson, Zhongcheng Xin, Guiting Lin, and Hengming Ke Zhongcheng Xin, Guiting Lin and Hengming Jackie D. Corbin, Howard Robinson, Jiwen Cai, Roya Zoraghi, Sharron H. Francis, Huanchen Wang, Yudong Liu, Qing Huai, Multiple Conformations of Phosphodiesterase-5: implications for enzyme function and drug development, The Journal of Biological Chemistry VOL. 281, NO. 30, pp. 21469–21479, July 28, 2006
25. ↑ Wang H, Liu Y, Huai Q, Cai J, Zoraghi R, Francis SH, Corbin JD, Robinson H, Xin Z, Lin G, Ke H. Multiple conformations of phosphodiesterase-5: implications for enzyme function and drug development. J Biol Chem 281: 21469–21479, 2006.
26. ↑ Sharron H. Francis, Mitsi A. Blount, And Jackie D. Corbin, Mammalian Cyclic Nucleotide Phosphodiesterases: Molecular Mechanisms and Physiological Functions, Physiol Rev 91:651-690, 2011. doi:10.1152/physrev.00030.2010
27. ↑ Sharron H. Francis, Mitsi A. Blount, And Jackie D. Corbin, Mammalian Cyclic Nucleotide Phosphodiesterases: Molecular Mechanisms and Physiological Functions, Physiol Rev 91:651-690, 2011. doi:10.1152/physrev.00030.2010
28. ↑ Agostino PV, Plano SA, Golombek DA. Sildenafil accelerates reentrainment of circadian rhythms after advancing light schedules. Proc Natl Acad Sci USA 104: 9834–9839, 2007.
29. ↑ Zhang L, Zhang RL, Wang Y, Zhang C, Zhang ZG, Meng H, Chopp M. Functional recovery in aged and young rats after embolic stroke: treatment with a phosphodiesterase type 5 inhibitor. Stroke 36: 847–852, 2005.
    Zhang L, Zhang Z, Zhang RL, Cui Y, LaPointe MC, Silver B, Chopp M. Tadalafil, a long-acting type 5 phosphodiesterase isoenzyme inhibitor, improves neurological functional recovery in a rat model of embolic stroke. Brain Res 1118: 192–198, 2006.
    Zhang R, Wang Y, Zhang L, Zhang Z, Tsang W, Lu M, Zhang L, Chopp M. Sildenafil (Viagra) induces neurogenesis and promotes functional recovery after stroke in rats. Stroke 33: 2675–2680, 2002.
    Zhang RL, Zhang Z, Zhang L, Wang Y, Zhang C, Chopp M. Delayed treatment with sildenafil enhances neurogenesis and improves functional recovery in aged rats after focal cerebral ischemia. J Neurosci Res 83: 1213–1219, 2006.
30. ↑ Menniti FS, Ren J, Coskran TM, Liu J, Morton D, Sietsma DK, Som A, Stephenson DT, Tate BA, Finklestein SP. Phosphodiesterase 5A inhibitors improve functional recovery after stroke in rats: optimized dosing regimen with implications for mechanism. J Pharmacol Exp Ther 331: 842–850, 2009.
31. ↑ Asai A, Sahani N, Kaneki M, Ouchi Y, Martyn JA, Yasuhara SE. Primary role of functional ischemia, quantitative evidence for the two-hit mechanism, and phosphodiesterase-5 inhibitor therapy in mouse muscular dystrophy. PLoS One 2: e806, 2007. Kobayashi YM, Rader EP, Crawford RW, Iyengar NK, Thedens DR, Faulkner JA, Parikh SV, Weiss RM, Chamberlain JS, Moore SA, Campbell KP. Sarcolemma-localized nNOS is required to maintain activity after mild exercise. Nature 456: 511–515, 2008.
32. ↑ Verhoest PR, Proulx-Lafrance C, Corman M, Chenard L, Helal CJ, Hou X, Kleiman R, Liu S, Marr E, Menniti FS, Schmidt CJ, Vanase-Frawley M, Schmidt AW, Williams RD, Nelson FR, Fonseca KR, Liras S. Identification of a brain penetrant PDE9A inhibitor utilizing prospective design and chemical enablement as a rapid lead optimization strategy. J Med Chem 52: 7946–7949, 2009. Rutten K, Van Donkelaar EL, Ferrington L, Blokland A, Bollen E, Steinbusch HW, Kelly PA, Prickaerts JH. Phosphodiesterase inhibitors enhance object memory independent of cerebral blood flow and glucose utilization in rats. Neuropsychopharmacology 34: 1914–1925, 2009 Rutten K, Vente JD, Sik A, Ittersum MM, Prickaerts J, Blokland A. The selective PDE5 inhibitor, sildenafil, improves object memory in Swiss mice and increases cGMP levels in hippocampal slices. Behav Brain Res 164: 11–16, 2005. Schmidt CJ. Phosphodiesterase inhibitors as potential cognition enhancing agents. Curr Top Med Chem 10: 222–230, 2010. Walter U, Gambaryan S. cGMP and cGMP-dependent protein kinase in platelets and blood cells. Handb Exp Pharmacol 533–548, 2009.
33. ↑ Liebenberg N, Harvey BH, Brand L, Brink CB. Antidepressant-like properties of phosphodiesterase type 5 inhibitors and cholinergic dependency in a genetic rat model of depression. Behav Pharmacol 21: 540–547, 2010.
34. ↑ Kemp-Harper B, Schmidt HH. cGMP in the vasculature. Handb Exp Pharmacol 447–467, 2009.
35. ↑ Aversa A, Bruzziches R, Vitale C, Marazzi G, Francomano D, Barbaro G, Spera G, Rosano GM. Chronic sildenafil in men with diabetes and erectile dysfunction. Expert Opin Drug Metab Toxicol 3: 451–464, 2007. Rosano GM, Aversa A, Vitale C, Fabbri A, Fini M, Spera G. Chronic treatment with tadalafil improves endothelial function in men with increased cardiovascular risk. Eur Urol 47: 214–220, 2005.
36. ↑ Bremer YA, Salloum F, Ockaili R, Chou E, Moskowitz WB, Kukreja RC. Sildenafil citrate (viagra) induces cardioprotective effects after ischemia/reperfusion injury in infant rabbits. Pediatr Res 57: 22–27, 2005. Fisher PW, Salloum F, Das A, Hyder H, Kukreja RC. Phosphodiesterase- 5 inhibition with sildenafil attenuates cardiomyocyte apoptosis and left ventricular dysfunction in a chronic model of doxorubicin cardiotoxicity. Circulation 111: 1601–1610, 2005. Kukreja RC, Salloum F, Das A, Ockaili R, Yin C, Bremer YA, Fisher PW, Wittkamp M, Hawkins J, Chou E, Kukreja AK, Wang X, Marwaha VR, Xi L. Pharmacological preconditioning with sildenafil: basic mechanisms and clinical implications. Vascul Pharmacol 42: 219–232, 2005. Sahara M, Sata M, Morita T, Nakajima T, Hirata Y, Nagai R. A phosphodiesterase-5 inhibitor vardenafil enhances angiogenesis through a protein kinase G-dependent hypoxia-inducible factor-1/ vascular endothelial growth factor pathway. Arterioscler Thromb Vasc Biol 30: 1315–1324, 2010. Salloum FN, Abbate A, Das A, Houser JE, Mudrick CA, Qureshi IZ, Hoke NN, Roy SK, Brown WR, Prabhakar S, Kukreja RC. Sildenafil (Viagra) attenuates ischemic cardiomyopathy and improves left ventricular function in mice. Am J Physiol Heart Circ Physiol 294: H1398–H1406, 2008. Salloum FN, Chau VQ, Hoke NN, Abbate A, Varma A, Ockaili RA, Toldo S, Kukreja RC. Phosphodiesterase-5 inhibitor, tadalafil, protects against myocardial ischemia/reperfusion through protein- kinase g-dependent generation of hydrogen sulfide. Circulation 120: S31–S36, 2009. Salloum FN, Ockaili RA, Wittkamp M, Marwaha VR, Kukreja RC. Vardenafil: a novel type 5 phosphodiesterase inhibitor reduces myocardial infarct size following ischemia/reperfusion injury via opening of mitochondrial K(ATP) channels in rabbits. J Mol Cell Cardiol 40: 405–411, 2006. Takimoto E, Champion HC, Li M, Belardi D, Ren S, Rodriguez ER, Bedja D, Gabrielson KL, Wang Y, Kass DA. Chronic inhibition of cyclic GMP phosphodiesterase 5A prevents and reverses cardiac hypertrophy. Nat Med 11: 214–222, 2005.
37. ↑ Abadi AH, Abouel-Ella DA, Ahmed NS, Gary BD, Thaiparambil JT, Tinsley HN, Keeton AB, Piazza GA. Synthesis of novel tadalafil analogues and their evaluation as phosphodiesterase inhibitors and anticancer agents. Arzneimittelforschung 59: 415– 421, 2009
38. ↑ Byung-Je Sung, Kwang Yeon Hwang, Young Ho Jeon, Jae Il Lee, Yong-Seok Heo, Jin Hwan Kim, Jinho Moon, Jung Min Yoon, Young-Lan Hyun, Eunmi Kim, Sung Jin Eum, Sam-Yong Park, Jie-Oh Lee, Tae Gyu Lee, Seonggu Ro & Joong Myung Cho, Structure of the catalytic domain of human phosphodiesterase 5 with bound drug molecules, NATURE, VOL 425, 4 SEPTEMBER 2003
39. ↑ Huanchen Wang, Yudong Liu, Qing Huai, Jiwen Cai, Roya Zoraghi, Sharron H. Francis, Jackie D. Corbin, Howard Robinson, Zhongcheng Xin, Guiting Lin, and Hengming Ke Zhongcheng Xin, Guiting Lin and Hengming Jackie D. Corbin, Howard Robinson, Jiwen Cai, Roya Zoraghi, Sharron H. Francis, Huanchen Wang, Yudong Liu, Qing Huai, Multiple Conformations of Phosphodiesterase-5: implications for enzyme function and drug development, The Journal of Biological Chemistry VOL. 281, NO. 30, pp. 21469–21479, July 28, 2006
40. ↑ Byung-Je Sung, Kwang Yeon Hwang, Young Ho Jeon, Jae Il Lee, Yong-Seok Heo, Jin Hwan Kim, Jinho Moon, Jung Min Yoon, Young-Lan Hyun, Eunmi Kim, Sung Jin Eum, Sam-Yong Park, Jie-Oh Lee, Tae Gyu Lee, Seonggu Ro & Joong Myung Cho, Structure of the catalytic domain of human phosphodiesterase 5 with bound drug molecules, NATURE, VOL 425, 4 SEPTEMBER 2003
41. ↑ Huanchen Wang, Yudong Liu, Qing Huai, Jiwen Cai, Roya Zoraghi, Sharron H. Francis, Jackie D. Corbin, Howard Robinson, Zhongcheng Xin, Guiting Lin, and Hengming Ke Zhongcheng Xin, Guiting Lin and Hengming Jackie D. Corbin, Howard Robinson, Jiwen Cai, Roya Zoraghi, Sharron H. Francis, Huanchen Wang, Yudong Liu, Qing Huai, Multiple Conformations of Phosphodiesterase-5: implications for enzyme function and drug development, The Journal of Biological Chemistry VOL. 281, NO. 30, pp. 21469–21479, July 28, 2006
42. ↑ Huanchen Wang, Yudong Liu, Qing Huai, Jiwen Cai, Roya Zoraghi, Sharron H. Francis, Jackie D. Corbin, Howard Robinson, Zhongcheng Xin, Guiting Lin, and Hengming Ke Zhongcheng Xin, Guiting Lin and Hengming Jackie D. Corbin, Howard Robinson, Jiwen Cai, Roya Zoraghi, Sharron H. Francis, Huanchen Wang, Yudong Liu, Qing Huai, Multiple Conformations of Phosphodiesterase-5: implications for enzyme function and drug development, The Journal of Biological Chemistry VOL. 281, NO. 30, pp. 21469–21479, July 28, 2006
43. ↑ Huanchen Wang, Yudong Liu, Qing Huai, Jiwen Cai, Roya Zoraghi, Sharron H. Francis, Jackie D. Corbin, Howard Robinson, Zhongcheng Xin, Guiting Lin, and Hengming Ke Zhongcheng Xin, Guiting Lin and Hengming Jackie D. Corbin, Howard Robinson, Jiwen Cai, Roya Zoraghi, Sharron H. Francis, Huanchen Wang, Yudong Liu, Qing Huai, Multiple Conformations of Phosphodiesterase-5: implications for enzyme function and drug development, The Journal of Biological Chemistry VOL. 281, NO. 30, pp. 21469–21479, July 28, 2006
44. ↑ Okada D, Asakawa S. Allosteric activation of cGMP-specific, cGMP-binding phosphodiesterase (PDE5) by cGMP. Biochemistry 41: 9672–9679, 2002 Weber G. Energetics of ligand binding to protein. Adv Protein Chem 29: 1–83, 1975. Bessay EP, Blount MA, Zoraghi R, Beasley A, Grimes KA, Francis SH, Corbin JD. Phosphorylation increases affinity of the phosphodiesterase-5 catalytic site for tadalafil. J Pharmacol Exp Ther 325: 62–68, 2008.
45. ↑ Bessay EP, Zoraghi R, Blount MA, Grimes KA, Beasley A, Francis SH, Corbin JD. Phosphorylation of phosphodiesterase-5 is promoted by a conformational change induced by sildenafil, vardenafil, or tadalafil. Front Biosci 12: 1899–1910, 2007.
46. ↑ JD Corbin, Mechanisms of action of PDE5 inhibition in erectile dysfunction, International Journal of Impotence Research (2004) 16, S4–S7
47. ↑ JD Corbin, Mechanisms of action of PDE5 inhibition in erectile dysfunction, International Journal of Impotence Research (2004) 16, S4–S7