Levinthal's Paradox—How Do Proteins Know How to Fold?

Even a simple protein made up of 100 amino acids may have as many as 3^{198}\approx 3\times 10^{94} ways in which it can fold. If it explored every possible configuration at a rate of a billion to a trillion per second, it would take longer than the age of the universe to find the unique configuration observed for these proteins in biology. In fact, biological proteins spontaneously fold into their unique functional configurations within milliseconds. Levinthal’s paradox asks how do they do it?