<p>Phosphoserine phosphatases (PSP) are members of a large group of enzymes responsible for phosphoester hydrolysis using a phosphoaspartate-enzyme intermediate. Reversible protein phosphorylation is essential for regulation of basic cell function such as DNA replication, gene transcription and protein translation. The phosphoserine phosphatases are related to the P-type ATPases and haloacid dehydrogenases, with which they share 3 conserved sequence motifs [<cite idref="PUB00054023"/>].</p><p>The crystal structures of PSP, PSP in complex with its substrate and in complex with a transition state analogue have been solved, giving extensive insight into the catalytic mechanism of phosphoserine phosphatases [<cite idref="PUB00026951"/>]. This entry represents the second domain, which is predominantly alpha helical. </p>