Levinthal paradox

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The Levinthal paradox is a paradox in the theory of protein folding. In 1969 Cyrus Levinthal noted, that because of the very high number of atoms in a typical protein, an astronomical number of possible conformations are possible (10³⁰⁰ is mentioned in the original work). If the protein is to try all the available conformations, then it would take longer than the age of earth to fold, even though a very rapid sampling of conformations is assumed. However most proteins rapidly go to one single conformation within milliseconds. Even though a very rapid sampling of conformations is assumed, the protein can only try a vanishing fraction of the available conformations in this time frame. The paradox is that the protein (almost) always finds the correct structure, even though it's search is far from exhaustive in terms of how much of the available conformation space it probes.

It has been argued that the paradox can be settled if the protein folds along a funnel like energy landscape rather than searching at random in conformation space.

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