A new ATP-binding fold in actin, hexokinase and Hsc70

One of a cell biologist's favourite occupations is to discover the proteins that perform newly described functions in the cell. Very often lately, this has resulted in the identification of protein families whose related amino acid sequences reflect similar functions, but can proteins with totally unrelated sequences have similar structures and functions? In this review, Ken Holmes, Chris Sander and Alfonso Valencia describe the structural similarities between three well-known proteins that have no readily detectable primary sequence similarities but for which X-ray crystallography has revealed very similar structures. A comparison of their structures provides insights into their common mechanisms of action and into protein evolution, and has been used to detect related proteins in sequence data bases.