This is a movie showing the sliding motion of a protein that transports calcium ions across the cell membrane. Though scientists had known the outward facing structure of a related protein, only now have they discovered the inward facing shape. Changes between the inner and outer structure of this protein allow the sliding motion shown here, which in turn facilities cation binding and transport. This video relates to a paper that appeared in the May 23, 2013, issue of Science Express, published by AAAS. The paper, by Tomohiro Nishizawa at University of Tokyo in Tokyo, Japan, and colleagues, was titled, "Structural Basis for the Counter-Transport Mechanism of a H+/Ca2+ Exchanger."