Classification of Supersecondary Structures in Proteins Using the   Automated Protein Structure Analysis Method
  The Automated Protein Structure Analysis (APSA) method is used for the classification of supersecondary structures. Basis for the classification is the encoding of three-dimensional (3D) residue conformations into a 16-letter code (3D-1D projection). It is shown that the letter code of the protein makes it possible to reconstruct its overall shape without ambiguity (1D-3D translation). Accordingly, the letter code is used for the development of classification rules that distinguish supersecondary structures by the properties of their turns and the orientation of the flanking helix or strand structures. The orientations of turn and flanking structures are collected in an octant system that helps to specify 196 supersecondary groups for (alpha,alpha)-, (alpha,beta)-, (beta,alpha)-, (beta,beta)-class. 391 protein chains leading to 2499 super secondary structures were analyzed. Frequently occurring super secondary structures are identified with the help of the octant classification system and explained on the basis of their letter and classification codes. 
Sushilee Ranganathan, Dmitry Izotov, Elfi Kraka, and Dieter Cremer