In hundreds of studies, researchers have zoomed in on its normal and subverted functions in ever greater detail. Normal Src conveys growth signals from the cell's outside to its inside. It does so by tacking phosphate groups onto tyrosine amino acids in other proteins, in a process called phosphorylation. Src must be a sort of multiplex switch, for it receives different types of input and, in response, turns on or off. More than scientific curiosity, this question is key to attempts to interfere therapeutically, says Harrison.
Most people think of proteins simply as tiny blobs.
But when Eck, Harrison, and postdoc Wenquin Xu scrutinized the structure of Src, they realized that it is a formidable product of nano-engineering. Src is a fancy little machine. Previous research had visualized parts of Src, but this is the first study that puts them together into a broader vista of how the parts interact. To their surprise, the researchers found that several mechanisms are at work simultaneously to keep Src idle, says Eck. For another, the SH3 domain turns its binding surface inward and snuggles up against the surface of one of the stretches linking two lobes.