Accumulating work over the past decade has shown that peptide aptamer screening 
represents a valid strategy for inhibitor identification that can be applied to 
a variety of different targets. Because of the screening method in cells and the 
highly combinatorial libraries available, this approach yields rapidly highly 
specific candidate inhibitors. Once a hit peptide has been identified, its 
interaction strength and affinity towards its target protein can be optimized 
even more, in order to increase its inhibition efficiency when subsequently 
applied in vivo. A condition to a successful optimization is that gain of 
inhibition strength should not result in loss of specificity. Here we present a 
simple method for peptide aptamer optimization, which can be achieved by 
PCR-based random mutagenesis combined with a selection screen in yeast using a 
strong selective drug. The rationale of this approach, which has proven valid 
and efficient, is that stronger interaction in yeast will also lead to stronger 
inhibition. Our optimization method is effective, without loss of specificity, 
which is of a great importance for the discovery of inhibitors that target 
specific protein-protein interactions.