Protein Engineering Through Chemical Synthesis - Design and Synthesis of Betabellin-4 and Betabellin-5

Betabellin (beta-barrel bell-shaped protein) was designed to provide a framework for the construction of binding and active sites. Its two identical peptide chains are COOH-terminally cross-linked by a symmetric diamino acid. Each chain should fold into an amphiphilic 4-stranded anti-parallel beta-pleated sheet. Each 32-residue chain of betabellin 4 is shown below, where Abu = 4-aminobutyric acid and Phi = 4-iodophenylalanine. Cross-linker X is 3,5-bis(aminoethyl)benzoic acid (Bab). A disulfide bridge between the two Cys-21 residues increases structural rigidity. Betabellin 5 contains D-amino acids at six positions in each chain (Pro, Asn). Betabellins 4 and 5 were synthesized from Boc/sub 2/Bab-Abu-NH-resin by simultaneous solid-phase assembly of both chains and were purified by gel filtration and centrifugal partition chromatography. CD and NMR studies indicate substantial beta-sheet structure.