Are there Unfoldable Proteins in Dimension Three?

In this paper we show the existence of three dimensional rigid, and thus unfoldable, lattice conformations. The structure we found has 450+ bonds, and we provide a computer assisted proof of the existence of such structures. The existence of such rigid structures illustrates why protein folding problems are hard also in dimension three. The existence of two rigid two dimensional structures was shown earlier. This work answers question 8 in \cite{2D} in the affirmative: rigid self avoiding walks exist in three dimensional lattice configurations.