Structure of Biological "Transistor" Detailed in Higher Organisms

The electro-mechanics of the potassium channel found in nerve cell membranes is yielding to study by x-ray diffraction, just as the structure of DNA did. The trick was getting pure crystals of the protein involved in opening and closing this molecular door. This is the type of research cited in Nobel awards. HHMI News: "The researchers analyzed the structure of a Kv1.2 channel from the rat using x-ray crystallography. In this analytical technique, intense beams of x-rays are directed through crystals of proteins. The underlying atomic structure of the proteins is deduced by analyzing the pattern of diffraction of the x-rays. The researchers had to overcome a major technical challenge to produce pure crystals of the Kv1.2 channel protein. The scientists developed a technique to crystallize the protein while maintaining it in a mixture of detergent and lipid - which more closely mimicked the oily cell membrane in which the channel exists naturally. 'This is a significant technical advance that I hope will turn out to be important for crystallization of other membrane proteins,' said MacKinnon. ... The researchers' earlier structural studies of the bacterial channel revealed that the voltage-sensing molecular 'paddles' control potassium flow by snapping open or shut. However, said MacKinnon, understanding the precise mechanism of this movement was thwarted because the voltage-sensing structure was contorted in the crystallized bacterial protein. 'We could deduce some things about how the voltage sensor worked,' he said. 'But identifying this voltage-sensor paddle led us to experiments that told us that this paddle moves a lot through the membrane when the channel opens. However, that channel couldn't really tell us how the paddle attached to the pore to open and close it.' The crystals of the Kv1.2 channel preserved the natural conformation of the voltage sensor. This enabled the researchers to discern that the paddle was attached by a hinge-like 'linker' that is coupled to the pore through which potassium flows. 'This connection was totally broken in the earlier structure, so we couldn't say anything about how the motions of the voltage sensor are coupled to the pore,' said MacKinnon. 'That had to be left to complete speculation.'”