I am working on protein design for antibody-antigen complex to improve the binding affinity. so far, I have the crystal structure of the antigen (chain A) and the antibody Fab (chain H and L). now I want to re-design part region of one CDR loop (around 5 residues) involved in direct interaction to antigen. besides the design for the loop retaining original length (5 AA), I also try to make the loop shorter or longer with the randomizing the residues of loop.
any suggestion that where I can start from?