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Christian Anfinsen worked with ribonuclease A, a protein that degrades RNA to determine its activity. He exposed ribonuclease A to urea and Beta-Mercaptoethanol to denature it (aka, it unfolds).
He found that urea disrupts the protein interactions required for folding. Similarly, Beta-mercaptoethanol disrupted disulfide bonds which were also important for folding. By adding both of these, he was causing the protein to lose all covalent and static stability which led to denaturing.
Further, when he took the denaturing agents away, the protein refolded! This allowed it to regain its function.
Ultimately, this showed that protein folding is sequence driven and is inherent to the primary sequence.
The ability of a protein to quickly fold into correct orientation proposes what is termed Levinthal's Paradox. Due to how large proteins can be (hundreds of residues long), it would take an impossibly long amount of time for every molecule to "test out" binding to every molecule in order to form the correct folding sequence. This paradox points out that it would in fact take about 10^34 years for the proper folding to occur. The fact that folding only takes a few moments shows that protein folding is not random and takes a dedicated route in order for proteins to fold quickly and efficiently.
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