The authors first obtained the crystal structure of a Ca2+ - gated K+ ion channel and then deciphered how ion channels open and close, a process called "gating" in response to cues in their environment. They determined the structure of the opened state and revealed the complex molecular nature of the way gating transitions occur.
In 2003 Roderick MacKinnon shared the Nobel Prize in Chemistry Peter Agre with  “for discoveries concerning channels in cell membranes."

Order of authorship in the original publication: Jiang, Lee, Chen...MacKinnon.

(Thanks for Juan Weiss for this reference and its interpretation.)