Oligomeric beta(beta)(alpha) miniprotein motifs: pivotal role of single hinge residue in determining the oligomeric state.

The role of a single glycine hinge residue in the structure of BBAT1, a beta(beta)(alpha) peptide that forms a discrete homotrimeric structure in solution, was evaluated with 11 new peptide sequences which differ only in the identity of the residue at the hinge position. The integrity of the structure and oligomeric state of the peptides was evaluated by using a combination of analytical ultracentrifugation and circular dichroism spectroscopy. Initially, it was discovered that the glycine hinge adopts backbone dihedral angles favored in D-amino acids and that incorporation of D-alanine at the hinge position stabilizes the trimer species. Subsequently, the effect of the side chains of different D-amino acids at the hinge position was evaluated. While incorporation of polar amino acids led to a destabilization of the oligomeric form of the peptide, only peptides including D-Ser or D-Asp at the hinge position were able to achieve a discrete trimer species. Incorporation of hydrophobic amino acids D-Leu and D-Phe led to oligomerization beyond a trimer to a tetrameric form. The dramatic differences among the thermodynamic stabilities and oligomeric states of these peptides illustrates the pivotal role of the hinge residue in the oligomerization of the beta(beta)(alpha) peptides.