Most of us have to teach about protein structure. We know the drill: primary structure being the linear sequence of amino acids, secondary involving the folding of portions of this chain into an alpha helix or beta pleated sheet. Then comes tertiary, where these segments and the sequences linking them are further folded into less regular and more complex forms. Finally, for proteins made up of several chains, there is a further level of structure, the quaternary, describing how these subunits come together to form the full molecule. I can remember learning this more than 40 years ago, so this hierarchy has been around a long time, though the number of examples of each structural level has grown tremendously since then. In the 1960s, only a few proteins had been sequenced and even fewer had been worked out structurally. But the basics were known even “back then.” This makes it...
University of California Press