Re-engineering a beta-lactamase using prototype peptides from a library of local structural motifs.

B. licheniformis exo-small beta-lactamase (ESBL) has a complex architecture with twelve alpha helices and a five-stranded beta sheet. We replaced, separately or simultaneously, three of the ESBL alpha helices with prototype amphiphatic helices from a catalog of secondary structure elements. Although the substitutes bear no sequence similarity to the originals and pertain to unrelated protein families, all the engineered ESBL variants were found able to fold in native like structures with in vitro and in vivo enzymic activity. The triple substituted variant resembles a primitive protein, with folding defects such as a strong tendency to oligomerization and very low stability; however it mimics a non homologous recombinant abandoning the family sequence space while preserving fold. The results test protein folding and evolution theories.