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Figure 6. Ribbon drawings . . .Click to Enlarge Image

Protein chains can fold into an enormous range of structures, but a few basic localized folds, or secondary structures, are widespread. The most common of these are alpha helices and beta sheets. The sequence of amino acids in a protein generally determines its three-dimensional shape, but researchers are still struggling to decipher the underlying grammar that links sequence to structure. Even understanding the formation of a basic beta-sheet structure has been difficult. Amino acids that make up a structure are often far apart in sequence, and understanding their long-range chemical interactions is an intricate problem. Recent experiments with one protein—the tailspike protein of a virus that infects Salmonella—have contributed a great deal to the understanding of how a specific kind of beta-sheet structure, the beta coil, forms. This is a step toward solving the protein-folding problem—or how sequence determines fold. This remains an important problem to solve since the precise folding of a cell’s thousands of proteins is crucial to their function and a cell’s life.

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