Permutation of modules or secondary structure units creates proteins with basal enzymatic properties

The RNase activity of barnase mutants obtained by the permutation of modules or secondary structure units was investigated. Four of the 45 mutants had weak but distinct RNase activity, and they had unique optimum pHs and temperatures like natural enzymes. One of the active mutants had an ordered conformation, but the others did not. An active mutant having disordered conformation formed an ordered conformation in the presence of GMP, which is an inhibitor of this mutant. These results indicate that the amino acid sequences derived from barnase have sufficient plasticity to be rearranged into different proteins with basal enzymatic properties.