From Proteopediaproteopedia link
CRYSTAL STRUCTURE OF THE COMPLEX BETWEEN CALYCULIN A AND THE CATALYTIC SUBUNIT OF PROTEIN PHOSPHATASE 1
[PP1G_HUMAN] Protein phosphatase that associates with over 200 regulatory proteins to form highly specific holoenzymes which dephosphorylate hundreds of biological targets. Protein phosphatase 1 (PP1) is essential for cell division, and participates in the regulation of glycogen metabolism, muscle contractility and protein synthesis. Dephosphorylates RPS6KB1. Involved in regulation of ionic conductances and long-term synaptic plasticity. May play an important role in dephosphorylating substrates such as the postsynaptic density-associated Ca(2+)/calmodulin dependent protein kinase II. Component of the PTW/PP1 phosphatase complex, which plays a role in the control of chromatin structure and cell cycle progression during the transition from mitosis into interphase. 
Publication Abstract from PubMed
The crystal structure of the catalytic subunit of the protein phosphatase 1 (PP1), PP1 gamma, in complex with a marine toxin, calyculin A, was determined at 2.0 A resolution. The metal binding site contains the phosphate group of calyculin A and forms a tight network via the hydrophilic interactions between PP1 and calyculin A. Calyculin A is located in two of the three grooves, namely, in the hydrophobic groove and the acidic groove on the molecular surface. This is the first observation to note that the inhibitor adopts not a pseudocyclic conformation but an extended conformation in order to form a complex with the protein. The amino acid terminus of calyculin A contributes, in a limited manner, to the binding to PP1 gamma, which is consistent with findings from the studies of dose-inhibition analysis.
Crystal structure of the complex between calyculin A and the catalytic subunit of protein phosphatase 1.,Kita A, Matsunaga S, Takai A, Kataiwa H, Wakimoto T, Fusetani N, Isobe M, Miki K Structure. 2002 May;10(5):715-24. PMID:12015153
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.