**4. Protein engineering based on CS**αβ **motif scaffold**

Based on the scaffold, some CSαβ proteins have been engineered to exhibit new functions or changing of antimicrobial activities (Lin et al., 2007;Vita et al., 1999;Vita et al., 1995). Different approaches, including minimal residue substitution, functional epitope exchange, structural based modification and combinatorial chemistry have been employed to engineer the scaffold to exhibit new functions (Lin et al., 2007;Thevissen et al., 2007;Van Gaal et al., 2004;Vita et al., 1999;Vita et al., 1995;Zhao et al., 2004). Protein structure is important to the rational design of a protein scaffold. It does not only reveal the shape of a protein molecule but sidechain orientation of each residue. This information is crucial for investigating possible interactions between designed protein and its target.
