PDE5

PDE5 is a cGMP-specific phosphodiesterase that hydrolyzes cGMP and functions as a dimeric multidomain enzyme^[1]. Mechanistically, cGMP generated through nitric oxide-soluble guanylyl cyclase signaling provides the main substrate context for PDE5-dependent signal termination^[1]. PDE5 activity is further regulated by cGMP binding to the GAF A domain and by phosphorylation in smooth muscle cells^[2][3]. Compared with broader PDE families, PDE5 belongs to the cGMP-selective group, whereas PDE1, PDE2, PDE3, PDE10, and PDE11 hydrolyze both cAMP and cGMP^[4]. The PDE5A gene encodes PDE5, and human penile cavernosum studies identified PDE5A1, PDE5A2, and PDE5A3 isoforms^[5][6]. In disease-relevant studies, sildenafil improved exercise capacity, WHO functional class, and hemodynamics in symptomatic pulmonary arterial hypertension^[7]. For experimental and translational applications, PDE5 inhibitors support research on erectile dysfunction, pulmonary arterial hypertension, lower urinary tract symptoms, and NO/cGMP pathway pharmacology^[8][9]. GAF-domain biosensor work also supports PDE5-based tools for identifying compounds that modulate cGMP binding and catalytic regulation^[10].