Protein stabilization through phage display

RNase S consists of two proteolytic fragments of RNase A, residues 1-20 (S2 0) and residues 21-124 (S pro). A 15-mer peptide (S15p) with high affinity for S pro was selected from a phage display library. Peptide residues that are buried in the structure of the wild type complex are conserved in S15p though there are several changes at other positions, Isothermal titration c alorimetry studies show that the affinity of S15p is comparable to that of the wild type peptide at 25 degrees C. However, the magnitudes of Delta H d egrees and Delta C-p are lower for S15p, suggesting that the thermal stabil ity of the complex is enhanced. In agreement with this prediction, at pit 6 , the T-m of the S15p complex was found to he 10 degrees C higher than that of the wild type complex, This suggests that for proteins where fragment c omplementation systems exist, phage display can be used to find mutations t hat increase protein thermal stability. (C) 2000 Federation of European Bio chemical Societies, Published by Elsevier Science B.V. All rights reserved.