In this study, the structural motifs that can be represented as combinations of small motifs such as β-hairpins, S-, and Z-like β-sheets and βαβ-units, and the П-like module are described and analyzed. The П-module consists of connected elements of the β-strand-loop-β-strand type arranged in space so that its overall fold resembles a clip or the Greek letter П. In proteins, the П-module itself and the structural motifs containing it exhibit unique overall folds and have specific sequence patterns of the key hydrophobic, hydrophilic and glycine residues. All this together enables us to conclude that these structural motifs can fold independently of the remaining part of the molecule and can act as nuclei and/or "ready-made" building blocks in protein folding.
Keywords: conformation; loop; overall fold; protein structure; sequence pattern; α-helix.
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