Carola Hunte is a structural biologist and first author of a 2005 study of NhaA, the sodium/proton antiporter of Escherichia coli. The team determined a crystal structure in a state downregulated by pH, revealing a path from the cytoplasm toward a proposed ion-binding region within the cell membrane.[ref]
The arrangement of short helices and charged groups motivated an alternating access model: changes in the transporter would expose the relevant region toward different sides of the membrane. The paper distinguished the observed structure from the proposed movements and pH-regulatory mechanism.[ref]
That distinction connects two kinds of experiment. Transport measurements count movement of ions; a protein structure supplies candidate routes and interactions. Seeing a possible route in one conformation does not by itself measure transport rate or establish the complete cycle.
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