Proteins are long chain molecules of amino acids with a backbone of covalently bonded atoms.
There are approximately 100,000 different types of protein chains found in humans, but only between 1,000 and 2,000 distinct types of protein folds in all of nature. In an ongoing study at the Princeton, NJ-based NEC Research Institute, scientists used a computer to generate all possible backbone structures of a protein chain. Nearly 100 billion separate structures were generated, and the 5,000 most compact were identified as possible protein backbone candidates. This fold is one of a few small protein structures that are used repeatedly in nature. Zinc-finger structures are estimated to constitute as much as one percent of the proteins encoded in the human genome.