the inventors realized that the diversity generated by conventional methods may be limited by steric hindrance between amino acid residues in the three - dimensional structures of the resulting polypeptides . the steric hindrance may occur between amino acid residues at widely different positions in the amino acid sequences , e . g . between residues in two different domains of the 3d structure , and resulting polypeptides which include such steric hindrance may never be observed in the conventional recombination methods because they may be expressed in poor yields or may have poor activity or stability . the inventors developed a method to identify and alleviate such steric hindrance in the resulting polypeptides . in an alignment of the three - dimensional structures , steric hindrance is indicated when residues from two different structures are located within a certain distance . pairs of residues at corresponding positions in the amino acid sequences are not considered , and residues close to the surface are considered to be less prone to steric hindrance .