Peptidyl-prolyl cis/trans isomerases (PPIases; EC 5.2.1.8), such as PIN1, catalyze the cis/trans isomerization of peptidyl-prolyl peptide bonds. PIN1 is the only PPIase that specifically binds to phosphorylated ser/thr-pro motifs to catalytically regulate the post-phosphorylation conformation of its substrates. PIN1-catalyzed conformational regulation has a profound impact on key proteins involved in the regulation of cell growth, genotoxic and other stress responses, the immune response, germ cell development, neuronal differentiation, and survival. Both Drosophila and human DOD contain a WW domain for protein-protein interactions and a peptidylprolyl cis-trans isomerase (PPIase) domain, and they are related to the Ess1 cell division gene of Saccharomyces cerevisiae.