Slow thrombin in solution.

As a tool for understanding biological mechanisms, X-ray crystallography possesses unparalleled power to enlighten, resolve controversy and shift a field of study on to a secure new paradigm. Thanks largely to developments in crystallographic methods, the technique has become accessible to the general biochemist and we have thus witnessed an exponential increase in the number of protein structures deposited every year. It is now commonplace for several structures to be published of the same protein under different crystallization conditions, sometimes resulting in conflicting mechanistic interpretations. Such a controversy has arisen over thrombin's conformational response to Na+ co-ordination, and in this issue of Biochemical Journal, De Filippis and colleagues put the two structural models of thrombin allostery to the test by returning to the techniques of solution biochemistry.