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Tyrosine-612 in PDE5 contributes to higher affinity for vardenafil over sildenafil.

Corbin J, Francis S, Zoraghi R

Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232, USA. jackie.corbin@vanderbilt.edu

Despite close structural similarity, vardenafil (Levitra) is 32-fold more potent than sildenafil (Viagra) to inhibit cGMP-binding cGMP-specific PDE (PDE5); this is due to differences between their heterocyclic rings. In co-crystals with PDE5, one of the rings of vardenafil or sildenafil interacts with Tyr(612), a catalytic site AA, via (1) a hydrogen bond with a water molecule and (2) hydrophobic bonds. For mutant PDE5(Y612F), which ablates hydrogen-bonding potential, vardenafil or sildenafil inhibition was strengthened (2.2- or 3.0-fold, respectively), implying that the Tyr(612) hydroxyl is a negative determinant for these inhibitors. For mutant PDE5(Y612A), which ablates both hydrogen bonding and hydrophobic-bonding potential, vardenafil inhibition was weakened much more than sildenafil inhibition (122- and 26-fold, respectively), suggesting that hydrophobic bonds involving Tyr(612) are stronger for vardenafil than for sildenafil.

Published 2 May 2006 in Int J Impot Res, 18(3): 251-7.
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