Calcium ATPase (the calcium pump) is a transport protein that facilitates the movement of calcium ions across the cell membrane. It ensures low concentration of Ca ions (needed for cell signaling) inside the cell by driving them out of the cell across an electrochemical gradient. The calcium ATPase plays an important role in muscle contraction. Two STL files are provided here showing the calcium pump in different configurations: the first one is an open position with no Ca ions (PDB ID: 1IWO) versus the closed position (PDB ID: 1SU4).The two files provided here are 1SU4 and 1IWO from the PDB databank (http://www.pdb.org). The 1SU4 provides a crystal structure of calcium ATPase with two calcium ions bounded. THe 1IWO provides a crystal structure of calcium ATPase with no calcium ions inside the protein. The original PDB files were downloaded from the Protein Database website and then converted to VRML 2 WRL files using PyMOL. (see Aquaporin for more details on conversion instructions)