Stability of Designed Proteins Against Mutations

The stability of model proteins with designed sequences is assessed in terms of the number of sequences (obtained from the designed sequence through mutations), which fold into 5the ``native'' conformation. By a complete enumeration of the total number of sequences obtained by introducing up to 4 point mutations and up to 7 composition--conserving mutations (swapping of amino acids) in a 36mers chain, it is found that there are $10^8-10^9$ sequences which in the folding process target onto the ``native'' conformation. Consequently, proteins with designed sequences display a remarkable degree of stability and, to a large extent, of designability.