Biomolecules:
Proteins 2

Secondary Structure: The α Helix and ß Sheet

Like many other scientific discoveries, the discovery of proteins' secondary structure , or which groups of amino acids approach each other closely, has an interesting story. One morning in the spring of 1948 a scientist named Linus Pauling was at home with a cold. After getting bored with light reading, he asked his wife to get some paper and a pencil so he could work on one of his latest research interests, how a linear sequence of amino acids folds into a three-dimensional shape. He knew the structures of amino acids, since he and his collaborator, Robert Corey, had already discovered that the peptide bonds linking amino acids are planar (See the Proteins 1 module for a discussion of peptide bonds). But he had no idea how the straight chain could fold into the 3-D structure except for a hunch that hydrogen bonding was involved.

What is hydrogen bonding?

Working that morning with the paper, folding it into different shapes, Pauling discovered the α helix (lower left). Later, he and Corey also discovered the ß sheet (lower right). What is most remarkable about this feat is that Pauling and Corey discovered these two common elements of secondary structure (present in over 60% of known proteins) 8 years before the first crystal structure of a protein was determined in 1959. For this and other work in chemical bonding Linus Pauling received the Nobel Prize in Chemistry in 1954.

Secondary Structure