Complexity of protein folding.

It is believed that the native folded three-dimensional conformation of a protein is its lowest free energy state, or one of its lowest. It is shown here that both a two- and three-dimensional mathematical model describing the folding process as a free energy minimization problem is NP-hard. This means that the problem belongs to a large set of computational problems, assumed to be very hard ("conditionally intractable"). Some of the possible ramifications of this result are speculated upon.