Proposed conformational model for PDE5A.

<p>PDE5A contains a C-terminal catalytic domain and an N-terminal domain containing two GAF (c<u>G</u>MP-binding PDE, Anabaena <u>a</u>denylyl cyclase, Escherichia coli <u>F</u>hlA protein) domains a and b. GAF a can bind cGMP. The binding site is involved in cGMP negative-feedback loop. PDE5A has a confirmed phosphorylation site at Ser102 and a putative site at Ser104. Mutating ser102 and ser104 leads to highly active protein possibly induced by conformational changes. Adapted from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0107627#pone.0107627-Corbin2" target="_blank">[23]</a>.