 although 
 extensively studied , it has proved difficult to describe 
 in detail how potassium ion channels conduct cations and water . 
 we 
 present a computational study that , by using stratified umbrella sampling , 
 examines nearly an entire conduction event of the kv1.2/2.1 paddle 
 chimera and thereby identifies the expected stable configurations 
 of ions and waters in the selectivity filter of the channel . 
 we describe 
 in detail the motions of the ions and waters during a conduction event , 
 focusing on how waters and ions enter the filter , the rotation of 
 water molecules inside the filter , and how potassium ions are coordinated 
 as they move from a water to a protein environment . 
 finally , we analyze 
 the small conformational changes undergone by the protein , showing 
 that the stable configurations are most similar to the experimental 
 crystal structure . 
Supplementary Material