A correctly folded protein adopts a very specific tertiary structure. This is the level at which secondary structure units such as alpha helices and beta sheets assemble into a specific three dimensional arrangement. This is also known as the fold.

Structural biologists have come up with a variety of colorful names for different sorts of tertiary folds such as beta sandwiches, helical bundles, beta barrels, greek-key motifs, propellors and many others.

See also:

protein

primary structure

secondary structure

quaternary structure