A computer based system and method determines, and displays possible chemical structures for converting two naturally aggregated but chemically separated polypeptide chains into a single polypeptide chain which will fold into a three dimensional structure very similar to the original structure made of the two polypeptide chains. A data base contains a large number of amino acid sequences for which the three dimensional structure is known. After plausible sites have been selected, this data base is examined to find which amino acid sequences (linkers) can bridge the gap between the plausible sites to create a plausible one-polypeptide structure. The testing of each possible linker proceeds in three steps. First, the span (a scaler quantity) of the candidate is compared to the span of the gap. If the span is close enough, step two is done which involves aligning the first peptides of the candidate with the initial peptide of the gap. The three dimensional vector from tail to head of the candidate is compared to the three dimensional vector from tail to head of the gap. If there is a sufficient match between the two vectors, step three is done, which involves fitting the termini of the candidate (using, for example, at least squares procedure) to the termini of the gap. If these two termini fit well enough, the candidate is enrolled for a ranking process.