DE-NOVO DESIGNED POLYPEPTIDE CATALYSTS WITH ADOPTED FOLDED STRUCTURES

Designed polypeptide catalysts have been shown to catalyze hydrolysis and transesterification reactions of p-nitrophenyl esters by a mechani sm that includes the nucleophilic attack by art unprotonated histidine and general-acid catalysis by a flanking protonated histidine, The ca talysis is cooperative and exhibits rate enhancements of three orders of magnitude over that of the 4-methylimidazole catalyzed reaction. Su bstrate recognition by residues introduced in the adjoining helix was demonstrated Sor the negatively charged substrate,mono-p-nitrophenyl f umarate. The results have been compared to those obtained for other de signed polypeptide catalysts with similar efficiency, and it was concl uded that the hallmarks of naturally occurring biocatalysts have now b een demonstrated in polypeptide catalyzed reactions, although with con siderably less efficiency than native enzymes. It was found that so fa r the most severe limitation of folded polypeptide catalysts is the ef ficiency obtained in the bond-making and bond-breaking steps, whereas the binding of substrates, even on the surface of helical structures i n aqueous solution, is of comparable strength to that which occurs in nature. (C) 1998 John Wiley & Sons, Inc.