Fig 1. Schematic representations of the architecture of the Rossmann fold.

The Rossmann is a β/α fold, namely a consecutive repeat of motifs comprising a β-strand (in yellow), a connecting loop (green), and α-helix (orange). The β-strands form a core β-sheet with the strands in the distinct order of 3-2-1–4-5-6. In effect, the Rossmann fold comprises two consecutive repeats, each comprising three β-strands (3-2-1 and 4-5-6), and two connecting α-helices. Shown in a red sphere is the ribose-binding Asp/Glu residue analyzed here, which resides at the tip of the second β-strand. Note that the Rossmann fold is usually addressed in the wider context, including Rossmann-like, or Rossmanoids, in which the sixth strand is missing, or is modified with additional secondary structural elements (e.g., methyltransferases).