Recurrent words found both in long and short loops. A long loop of 18 structural letters (central figure) extracted from protein with pdb code 3SIL contains four words (UOGI, KHBB, IFFR, RPBQ) of W set≥30. The protein is colored in gray, and the loop in blue except the four words UOGI in magenta, KHBB in cyan, IFFR in red and RPBQ in green. These four words are also seen in short loops in other structures. For each word, we indicate the structural letter pattern, the loop length within brackets and the pdb code of the protein structures. Structures are displayed with pymol .