For long time a lot of scientists have devoted to study how matter

such as water molecules and K+

Na+

Ca2+

Cl-ions

move through cell membranes and complete the matter exchange between the inside and outside of cells. Peter Agre discovered and characterized the first water channel protein in 1988 and Roderick MacKinnon elucidated the structural and mechanistic basis for ion channel function in 1998. These achievements have made it possible for us to "see" these exquisitely designed molecular machines in action at the atomic level. The Nobel Prize in Chemistry for 2003 is shared between these two scientists. In determining the high resolution 3D structure of these channels

the synchrotron X-ray diffraction plays an important role.