Cell 138, 774–786 (2009)

The traditional hierarchy of protein structure might require revision. Rama Ranganathan at the University of Texas Southwestern Medical Center in Dallas and his colleagues propose that proteins contain semi-independent clusters of co-evolving amino acids that they call 'protein sectors'.

The researchers analysed the conserved biological properties of the S1A protein family. They found that the proteins' amino acids are organized into three conserved functional units that are distinct from the classically observed structural hierarchies based on sequence or three-dimensional shape. As such, the authors argue, natural selection may operate at the level of these protein sectors.