Modèle ruban

Ribbon diagrams, also known as Richardson diagrams, are 3D schematic representations of protein structure and are one of the most common methods of protein depiction used today. The ribbon depicts the general course and organisation of the protein backbone in 3D and serves as a visual framework for hanging details of the entire atomic structure, such as the balls for the oxygen atoms attached to myoglobin's active site in the adjacent figure. Ribbon diagrams are generated by interpolating a smooth curve through the polypeptide backbone. α-helices are shown as coiled ribbons or thick tubes, β-strands as arrows, and non-repetitive coils or loops as lines or thin tubes. The direction of the polypeptide chain is shown locally by the arrows, and may be indicated overall by a colour ramp along the length of the ribbon. Ribbon diagrams are simple yet powerful, expressing the visual basics of a molecular structure (twist, fold and unfold). This method has successfully portrayed the overall organization of protein structures, reflecting their three-dimensional nature and allowing better understanding of these complex objects both by expert structural biologists and by other scientists, students, and the general public. The first ribbon diagrams, hand-drawn by Jane S. Richardson in 1980 (influenced by earlier individual illustrations), were the first schematics of 3D protein structure to be produced systematically. They were created to illustrate a classification of protein structures for an article in Advances in Protein Chemistry (now available in annotated form on-line at Anatax). These drawings were outlined in pen on tracing paper over a printout of a Cα trace of the atomic coordinates, and shaded with colored pencil or pastels; they preserved positions, smoothed the backbone path, and incorporated small local shifts to disambiguate the visual appearance. As well as the triose isomerase ribbon drawing at the right, other hand-drawn examples depicted prealbumin, flavodoxin, and Cu,Zn superoxide dismutase. In 1982, Arthur M.